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.TH LIBPNG 3 "March 31, 2011".SH NAMElibpng \- Portable Network Graphics (PNG) Reference Library 1.5.2.SH SYNOPSIS\fI\fB
\fB#include <png.h>\fP
\fI\fB
\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
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\fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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\fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
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\fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
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\fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
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\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
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\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
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\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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\fBpng_structp png_create_read_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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\fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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\fBpng_structp png_create_write_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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\fBvoid png_data_freer (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIfreer\fP\fB, png_uint_32 \fImask)\fP\fB);\fP
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\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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\fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
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\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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\fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
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\fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_bKGD (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
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\fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_cHRM (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
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\fBpng_uint_32 png_get_cHRM_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
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\fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
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\fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
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\fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_gAMA (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
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\fBpng_uint_32 png_get_gAMA_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
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\fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_hIST (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
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\fBpng_uint_32 png_get_iCCP (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_bytepp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
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\fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
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\fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
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\fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_const_bytep png_get_io_chunk_name (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_oFFs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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\fBpng_uint_32 png_get_pCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
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\fBpng_uint_32 png_get_pHYs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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\fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_pHYs_dpi (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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\fBpng_fixed_point png_get_pixel_aspect_ratio_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_PLTE (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
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\fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr)
\fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_sBIT (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
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\fBvoid png_get_sCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, double* \fP\fIwidth\fP\fB, double* \fIheight\fP\fB);\fP
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\fBvoid png_get_sCAL_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_fixed_pointp \fP\fIwidth\fP\fB, png_fixed_pointp \fIheight\fP\fB);\fP
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\fBvoid png_get_sCAL_s (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_charpp \fP\fIwidth\fP\fB, png_charpp \fIheight\fP\fB);\fP
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\fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_sPLT (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_sRGB (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int \fI*file_srgb_intent\fP\fB);\fP
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\fBpng_uint_32 png_get_text (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
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\fBpng_uint_32 png_get_tIME (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
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\fBpng_uint_32 png_get_tRNS (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans_alpha\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
\fI\fB
\fB/* This function is really an inline macro. \fI*/
\fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
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\fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
\fI\fB
\fB/* This function is really an inline macro. \fI*/
\fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
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\fBpng_uint_32 png_get_unknown_chunks (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
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\fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_valid (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
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\fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_x_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_x_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_y_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_y_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
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\fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
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\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
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\fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
\fI\fB
\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
\fI\fB
\fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
\fI\fB
\fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
\fI\fB
\fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
\fI\fB
\fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
\fI\fB
\fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
\fI\fB
\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
\fI\fB
\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
\fI\fB
\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
\fI\fB
\fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
\fI\fB
\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
\fI\fB
\fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
\fI\fB
\fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
\fI\fB
\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
\fI\fB
\fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
\fI\fB
\fBvoid png_set_background_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, png_uint_32 \fIbackground_gamma\fP\fB);\fP
\fI\fB
\fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
\fI\fB
\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
\fI\fB
\fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
\fI\fB
\fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
\fI\fB
\fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
\fI\fB
\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
\fI\fB
\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
\fI\fB
\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
\fI\fB
\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
\fI\fB
\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
\fI\fB
\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
\fI\fB
\fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
\fI\fB
\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
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\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
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\fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
\fI\fB
\fBvoid png_set_filter_heuristics_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_fixed_point_p \fP\fIfilter_weights\fP\fB, png_fixed_point_p \fIfilter_costs\fP\fB);\fP
\fI\fB
\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
\fI\fB
\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
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\fBvoid png_set_gamma_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIscreen_gamma\fP\fB, png_uint_32 \fIdefault_file_gamma\fP\fB);\fP
\fI\fB
\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
\fI\fB
\fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
\fI\fB
\fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
\fI\fB
\fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_const_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_const_bytep \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
\fI\fB
\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
\fI\fB
\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
\fI\fB
\fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
\fI\fB
\fBjmp_buf* png_set_longjmp_fn (png_structp \fP\fIpng_ptr\fP\fB, png_longjmp_ptr \fP\fIlongjmp_fn\fP\fB, size_t \fIjmp_buf_size\fP\fB);\fP
\fI\fB
\fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
\fI\fB
\fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
\fI\fB
\fBvoid png_set_mem_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
\fI\fB
\fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
\fI\fB
\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
\fI\fB
\fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
\fI\fB
\fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
\fI\fB
\fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
\fI\fB
\fBvoid png_set_quantize (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_quantize\fP\fB);\fP
\fI\fB
\fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
\fI\fB
\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
\fI\fB
\fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
\fI\fB
\fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
\fI\fB
\fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
\fI\fB
\fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_uint_32 \fP\fIred\fP\fB, png_uint_32 \fIgreen\fP\fB);\fP
\fI\fB
\fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
\fI\fB
\fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
\fI\fB
\fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
\fI\fB
\fBvoid png_set_sCAL_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_fixed_point \fP\fIwidth\fP\fB, png_fixed_point \fIheight\fP\fB);\fP
\fI\fB
\fBvoid png_set_sCAL_s (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_charp \fP\fIwidth\fP\fB, png_charp \fIheight\fP\fB);\fP
\fI\fB
\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
\fI\fB
\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
\fI\fB
\fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
\fI\fB
\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
\fI\fB
\fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
\fI\fB
\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
\fI\fB
\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
\fI\fB
\fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
\fI\fB
\fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans_alpha\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
\fI\fB
\fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
\fI\fB
\fBvoid png_set_unknown_chunk_location (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
\fI\fB
\fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
\fI\fB
\fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
\fI\fB
\fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
\fI\fB
\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
\fI\fB
\fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
\fI\fB
\fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
\fI\fB
\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
\fI\fB
\fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
\fI\fB
\fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
\fI\fB
\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
\fI\fB
\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
\fI\fB
\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
\fI\fB
\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
\fI\fB
\fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
\fI\fB
\fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
\fI\fB
\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
\fI\fB
.SH DESCRIPTIONThe.I libpnglibrary supports encoding, decoding, and various manipulations ofthe Portable Network Graphics (PNG) format image files. It uses the.IR zlib(3)compression library.Following is a copy of the libpng-manual.txt file that accompanies libpng..SH LIBPNG.TXTlibpng-manual.txt - A description on how to use and modify libpng
libpng version 1.5.2 - March 31, 2011 Updated and distributed by Glenn Randers-Pehrson <glennrp at users.sourceforge.net> Copyright (c) 1998-2011 Glenn Randers-Pehrson
This document is released under the libpng license. For conditions of distribution and use, see the disclaimer and license in png.h
Based on:
libpng versions 0.97, January 1998, through 1.5.2 - March 31, 2011 Updated and distributed by Glenn Randers-Pehrson Copyright (c) 1998-2011 Glenn Randers-Pehrson
libpng 1.0 beta 6 version 0.96 May 28, 1997 Updated and distributed by Andreas Dilger Copyright (c) 1996, 1997 Andreas Dilger
libpng 1.0 beta 2 - version 0.88 January 26, 1996 For conditions of distribution and use, see copyright notice in png.h. Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
Updated/rewritten per request in the libpng FAQ Copyright (c) 1995, 1996 Frank J. T. Wojcik December 18, 1995 & January 20, 1996
.SH I. Introduction
This file describes how to use and modify the PNG reference library(known as libpng) for your own use. There are five sections to thisfile: introduction, structures, reading, writing, and modification andconfiguration notes for various special platforms. In addition to thisfile, example.c is a good starting point for using the library, asit is heavily commented and should include everything most peoplewill need. We assume that libpng is already installed; see theINSTALL file for instructions on how to install libpng.
For examples of libpng usage, see the files "example.c", "pngtest.c",and the files in the "contrib" directory, all of which are included inthe libpng distribution.
Libpng was written as a companion to the PNG specification, as a wayof reducing the amount of time and effort it takes to support the PNGfile format in application programs.
The PNG specification (second edition), November 2003, is available asa W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at<http://www.w3.org/TR/2003/REC-PNG-20031110/The W3C and ISO documents have identical technical content.
The PNG-1.2 specification is available at<http://www.libpng.org/pub/png/documents/>. It is technically equivalentto the PNG specification (second edition) but has some additional material.
The PNG-1.0 specification is availableas RFC 2083 <http://www.libpng.org/pub/png/documents/> and as aW3C Recommendation <http://www.w3.org/TR/REC.png.html>.
Some additional chunks are described in the special-purpose public chunksdocuments at <http://www.libpng.org/pub/png/documents/>.
Other informationabout PNG, and the latest version of libpng, can be found at the PNG homepage, <http://www.libpng.org/pub/png/>.
Most users will not have to modify the library significantly; advancedusers may want to modify it more. All attempts were made to make it ascomplete as possible, while keeping the code easy to understand.Currently, this library only supports C. Support for other languagesis being considered.
Libpng has been designed to handle multiple sessions at one time,to be easily modifiable, to be portable to the vast majority ofmachines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easyto use. The ultimate goal of libpng is to promote the acceptance ofthe PNG file format in whatever way possible. While there is stillwork to be done (see the TODO file), libpng should cover themajority of the needs of its users.
Libpng uses zlib for its compression and decompression of PNG files.Further information about zlib, and the latest version of zlib, canbe found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.The zlib compression utility is a general purpose utility that isuseful for more than PNG files, and can be used without libpng.See the documentation delivered with zlib for more details.You can usually find the source files for the zlib utility wherever youfind the libpng source files.
Libpng is thread safe, provided the threads are using differentinstances of the structures. Each thread should have its ownpng_struct and png_info instances, and thus its own image.Libpng does not protect itself against two threads using thesame instance of a structure.
.SH II. Structures
There are two main structures that are important to libpng, png_structand png_info. Both are internal structures that are no longer exposedin the libpng interface (as of libpng 1.5.0).
The png_info structure is designed to provide information about thePNG file. At one time, the fields of png_info were intended to bedirectly accessible to the user. However, this tended to cause problemswith applications using dynamically loaded libraries, and as a resulta set of interface functions for png_info (the png_get_*() and png_set_*()functions) was developed.
The png_struct structure is the object used by the library to decode asingle image. As of 1.5.0 this structure is also not exposed.
Almost all libpng APIs require a pointer to a png_struct as the first argument.Many (in particular the png_set and png_get APIs) also require a pointerto png_info as the second argument. Some application visible macrosdefined in png.h designed for basic data access (reading and writingintegers in the PNG format) break this rule, but it's almost always safeto assume that a (png_struct*) has to be passed to call an API function.
The png.h header file is an invaluable reference for programming with libpng.And while I'm on the topic, make sure you include the libpng header file:
#include <png.h>
.SS Types
The png.h header file defines a number of integral types used by theAPIs. Most of these are fairly obvious; for example types correspondingto integers of particular sizes and types for passing color values.
One exception is how non-integral numbers are handled. For applicationconvenience most APIs that take such numbers have C (double) arguments,however internally PNG, and libpng, use 32 bit signed integers and encodethe value by multiplying by 100,000. As of libpng 1.5.0 a conveniencemacro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)which is simply (png_int_32).
All APIs that take (double) arguments also have an matching API thattakes the corresponding fixed point integer arguments. The fixed pointAPI has the same name as the floating point one with _fixed appended.The actual range of values permitted in the APIs is frequently less thanthe full range of (png_fixed_point) (-21474 to +21474). When APIs requirea non-negative argument the type is recorded as png_uint_32 above. Consultthe header file and the text below for more information.
Special care must be take with sCAL chunk handling because the chunk itselfuses non-integral values encoded as strings containing decimal floating pointnumbers. See the comments in the header file.
.SS Configuration
The main header file function declarations are frequently protected by Cpreprocessing directives of the form:
#ifdef PNG_feature_SUPPORTED declare-function #endif
The library can be built without support for these APIs, although astandard build will have all implemented APIs. Application programsshould check the feature macros before using an API for maximumportability. From libpng 1.5.0 the feature macros set during the buildof libpng are recorded in the header file "pnglibconf.h" and this fileis always included by png.h.
If you don't need to change the library configuration from the default skip tothe next section ("Reading").
Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) allof the build project files in the 'projects' directory simply copyscripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these buildsystems do not permit easy auto-configuration of the library - they onlysupport the default configuration.
The easiest way to make minor changes to the libpng configuration whenauto-configuration is supported is to add definitions to the command lineusing (typically) CPPFLAGS. For example:
CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC
will change the internal libpng math implementation for gamma correction andother arithmetic calculations to fixed point, avoiding the need for fastfloating point support. The result can be seen in the generated pnglibconf.h -make sure it contains the changed feature macro setting.
If you need to make more extensive configuration changes - more than one or twofeature macro settings - you can either add -DPNG_USER_CONFIG to the buildcommand line and put a list of feature macro settings in pngusr.h or you can setDFA_XTRA (a makefile variable) to a file containing the same information in theform of 'option' settings.
A. Changing pnglibconf.h
A variety of methods exist to build libpng. Not all of these supportreconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either berebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt and changingthe lines defining the supported features, paying very close attention to the'option' information in scripts/pnglibconf.dfa that describes those features andtheir requirements. This is easy to get wrong.
B. Configuration using DFA_XTRA
Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a latervariant such as 'nawk' or 'gawk', is available. The configure build willautomatically find an appropriate awk and build pnglibconf.h.scripts/pnglibconf.mak contains a set of make rules for doing the same thing ifconfigure is not used, and many of the makefiles in the scripts directory usethis approach.
When rebuilding simply write new file containing changed options and setDFA_XTRA to the name of this file. This causes the build to append the new fileto the end of scripts/pnglibconf.dfa. pngusr.dfa should contain lines of thefollowing forms:
everything = off
This turns all optional features off. Include it at the start of pngusr.dfa tomake it easier to build a minimal configuration. You will need to turn at leastsome features on afterward to enable either reading or writing code, or both.
option feature onoption feature off
Enable or disable a single feature. This will automatically enable otherfeatures required by a feature that is turned on or disable other features thatrequire a feature which is turned off. Conflicting settings will cause an errormessage to be emitted by awk.
setting feature default value
Changes the default value of setting 'feature' to 'value'. There are a smallnumber of settings listed at the top of pnglibconf.h, they are documented in thesource code. Most of these values have performance implications for the librarybut most of them have no visible effect on the API. Some can also be overriddenfrom the API.
C. Configuration using PNG_USR_CONFIG
If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the filepngusr.h will automatically be included before the options inscripts/pnglibconf.dfa are processed. pngusr.h should contain only macrodefinitions turning features on or off or setting settings.
Apart from the global setting "everything = off" all the options listed abovecan be set using macros in pngusr.h:
#define PNG_feature_SUPPORTED
is equivalent to:
option feature on
#define PNG_NO_feature
is equivalent to:
option feature off
#define PNG_feature value
is equivalent to:
setting feature default value
Notice that in both cases, pngusr.dfa and pngusr.h, the contents of thepngusr file you supply override the contents of scripts/pnglibconf.dfa
If confusing or incomprehensible behavior results it is possible toexamine the intermediate file pnglibconf.dfn to find the full set ofdependency information for each setting and option. Simply locate thefeature in the file and read the C comments that precede it.
.SH III. Reading
We'll now walk you through the possible functions to call when readingin a PNG file sequentially, briefly explaining the syntax and purposeof each one. See example.c and png.h for more detail. Whileprogressive reading is covered in the next section, you will stillneed some of the functions discussed in this section to read a PNGfile.
.SS Setup
You will want to do the I/O initialization(*) before you get into libpng,so if it doesn't work, you don't have much to undo. Of course, youwill also want to insure that you are, in fact, dealing with a PNGfile. Libpng provides a simple check to see if a file is a PNG file.To use it, pass in the first 1 to 8 bytes of the file to the functionpng_sig_cmp(), and it will return 0 (false) if the bytes match thecorresponding bytes of the PNG signature, or nonzero (true) otherwise.Of course, the more bytes you pass in, the greater the accuracy of theprediction.
If you are intending to keep the file pointer open for use in libpng,you must ensure you don't read more than 8 bytes from the beginningof the file, and you also have to make a call to png_set_sig_bytes_read()with the number of bytes you read from the beginning. Libpng willthen only check the bytes (if any) that your program didn't read.
(*): If you are not using the standard I/O functions, you will needto replace them with custom functions. See the discussion underCustomizing libpng.
FILE *fp = fopen(file_name, "rb"); if (!fp) { return (ERROR); }
fread(header, 1, number, fp); is_png = !png_sig_cmp(header, 0, number);
if (!is_png) { return (NOT_PNG); }
Next, png_struct and png_info need to be allocated and initialized. Inorder to ensure that the size of these structures is correct even with adynamically linked libpng, there are functions to initialize andallocate the structures. We also pass the library version, optionalpointers to error handling functions, and a pointer to a data struct foruse by the error functions, if necessary (the pointer and functions canbe NULL if the default error handlers are to be used). See the sectionon Changes to Libpng below regarding the old initialization functions.The structure allocation functions quietly return NULL if they fail tocreate the structure, so your application should check for that.
png_structp png_ptr = png_create_read_struct (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, user_error_fn, user_warning_fn);
if (!png_ptr) return (ERROR);
png_infop info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr) { png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL); return (ERROR); }
png_infop end_info = png_create_info_struct(png_ptr);
if (!end_info) { png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL); return (ERROR); }
If you want to use your own memory allocation routines,use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and usepng_create_read_struct_2() instead of png_create_read_struct():
png_structp png_ptr = png_create_read_struct_2 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, user_error_fn, user_warning_fn, (png_voidp) user_mem_ptr, user_malloc_fn, user_free_fn);
The error handling routines passed to png_create_read_struct()and the memory alloc/free routines passed to png_create_struct_2()are only necessary if you are not using the libpng supplied errorhandling and memory alloc/free functions.
When libpng encounters an error, it expects to longjmp backto your routine. Therefore, you will need to call setjmp and passyour png_jmpbuf(png_ptr). If you read the file from differentroutines, you will need to update the jmpbuf field every time you entera new routine that will call a png_*() function.
See your documentation of setjmp/longjmp for your compiler for moreinformation on setjmp/longjmp. See the discussion on libpng errorhandling in the Customizing Libpng section below for more informationon the libpng error handling. If an error occurs, and libpng longjmp'sback to your setjmp, you will want to call png_destroy_read_struct() tofree any memory.
if (setjmp(png_jmpbuf(png_ptr))) { png_destroy_read_struct(&png_ptr, &info_ptr, &end_info); fclose(fp); return (ERROR); }
If you would rather avoid the complexity of setjmp/longjmp issues,you can compile libpng with PNG_NO_SETJMP, in which caseerrors will result in a call to PNG_ABORT() which defaults to abort().
You can #define PNG_ABORT() to a function that does somethingmore useful than abort(), as long as your function does notreturn.
Now you need to set up the input code. The default for libpng is touse the C function fread(). If you use this, you will need to pass avalid FILE * in the function png_init_io(). Be sure that the file isopened in binary mode. If you wish to handle reading data in anotherway, you need not call the png_init_io() function, but you must thenimplement the libpng I/O methods discussed in the Customizing Libpngsection below.
png_init_io(png_ptr, fp);
If you had previously opened the file and read any of the signature fromthe beginning in order to see if this was a PNG file, you need to letlibpng know that there are some bytes missing from the start of the file.
png_set_sig_bytes(png_ptr, number);
You can change the zlib compression buffer size to be used whilereading compressed data with
png_set_compression_buffer_size(png_ptr, buffer_size);
where the default size is 8192 bytes. Note that the buffer sizeis changed immediately and the buffer is reallocated immediately,instead of setting a flag to be acted upon later.
If you want CRC errors to be handled in a different manner thanthe default, use
png_set_crc_action(png_ptr, crit_action, ancil_action);
The values for png_set_crc_action() say how libpng is to handle CRC errors inancillary and critical chunks, and whether to use the data containedtherein. Note that it is impossible to "discard" data in a criticalchunk.
Choices for (int) crit_action are PNG_CRC_DEFAULT 0 error/quit PNG_CRC_ERROR_QUIT 1 error/quit PNG_CRC_WARN_USE 3 warn/use data PNG_CRC_QUIET_USE 4 quiet/use data PNG_CRC_NO_CHANGE 5 use the current value
Choices for (int) ancil_action are PNG_CRC_DEFAULT 0 error/quit PNG_CRC_ERROR_QUIT 1 error/quit PNG_CRC_WARN_DISCARD 2 warn/discard data PNG_CRC_WARN_USE 3 warn/use data PNG_CRC_QUIET_USE 4 quiet/use data PNG_CRC_NO_CHANGE 5 use the current value
.SS Setting up callback code
You can set up a callback function to handle any unknown chunks in theinput stream. You must supply the function
read_chunk_callback(png_structp png_ptr, png_unknown_chunkp chunk); { /* The unknown chunk structure contains your chunk data, along with similar data for any other unknown chunks: */
png_byte name[5]; png_byte *data; png_size_t size;
/* Note that libpng has already taken care of the CRC handling */
/* put your code here. Search for your chunk in the unknown chunk structure, process it, and return one of the following: */
return (-n); /* chunk had an error */ return (0); /* did not recognize */ return (n); /* success */ }
(You can give your function another name that you like instead of"read_chunk_callback")
To inform libpng about your function, use
png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr, read_chunk_callback);
This names not only the callback function, but also a user pointer thatyou can retrieve with
png_get_user_chunk_ptr(png_ptr);
If you call the png_set_read_user_chunk_fn() function, then all unknownchunks will be saved when read, in case your callback function will needone or more of them. This behavior can be changed with thepng_set_keep_unknown_chunks() function, described below.
At this point, you can set up a callback function that will becalled after each row has been read, which you can use to controla progress meter or the like. It's demonstrated in pngtest.c.You must supply a function
void read_row_callback(png_structp png_ptr, png_uint_32 row, int pass); { /* put your code here */ }
(You can give it another name that you like instead of "read_row_callback")
To inform libpng about your function, use
png_set_read_status_fn(png_ptr, read_row_callback);
When this function is called the row has already been completely processed andthe 'row' and 'pass' refer to the next row to be handled. For thenon-interlaced case the row that was just handled is simply one less than thepassed in row number, and pass will always be 0. For the interlaced case thesame applies unless the row value is 0, in which case the row just handled wasthe last one from one of the preceding passes. Because interlacing may skip apass you cannot be sure that the preceding pass is just 'pass-1', if you reallyneed to know what the last pass is record (row,pass) from the callback and usethe last recorded value each time.
As with the user transform you can find the output row using thePNG_ROW_FROM_PASS_ROW macro.
.SS Unknown-chunk handling
Now you get to set the way the library processes unknown chunks in theinput PNG stream. Both known and unknown chunks will be read. Normalbehavior is that known chunks will be parsed into information invarious info_ptr members while unknown chunks will be discarded. Thisbehavior can be wasteful if your application will never use some knownchunk types. To change this, you can call:
png_set_keep_unknown_chunks(png_ptr, keep, chunk_list, num_chunks); keep - 0: default unknown chunk handling 1: ignore; do not keep 2: keep only if safe-to-copy 3: keep even if unsafe-to-copy
You can use these definitions: PNG_HANDLE_CHUNK_AS_DEFAULT 0 PNG_HANDLE_CHUNK_NEVER 1 PNG_HANDLE_CHUNK_IF_SAFE 2 PNG_HANDLE_CHUNK_ALWAYS 3
chunk_list - list of chunks affected (a byte string, five bytes per chunk, NULL or '\0' if num_chunks is 0)
num_chunks - number of chunks affected; if 0, all unknown chunks are affected. If nonzero, only the chunks in the list are affected
Unknown chunks declared in this way will be saved as raw data onto alist of png_unknown_chunk structures. If a chunk that is normallyknown to libpng is named in the list, it will be handled as unknown,according to the "keep" directive. If a chunk is named in successiveinstances of png_set_keep_unknown_chunks(), the final instance willtake precedence. The IHDR and IEND chunks should not be named inchunk_list; if they are, libpng will process them normally anyway.
Here is an example of the usage of png_set_keep_unknown_chunks(),where the private "vpAg" chunk will later be processed by a user chunkcallback function:
png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED) png_byte unused_chunks[]= { 104, 73, 83, 84, (png_byte) '\0', /* hIST */ 105, 84, 88, 116, (png_byte) '\0', /* iTXt */ 112, 67, 65, 76, (png_byte) '\0', /* pCAL */ 115, 67, 65, 76, (png_byte) '\0', /* sCAL */ 115, 80, 76, 84, (png_byte) '\0', /* sPLT */ 116, 73, 77, 69, (png_byte) '\0', /* tIME */ }; #endif
...
#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED) /* ignore all unknown chunks: */ png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
/* except for vpAg: */ png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
/* also ignore unused known chunks: */ png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks, (int)sizeof(unused_chunks)/5); #endif
.SS User limits
The PNG specification allows the width and height of an image to be aslarge as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.Since very few applications really need to process such large images,we have imposed an arbitrary 1-million limit on rows and columns.Larger images will be rejected immediately with a png_error() call. Ifyou wish to override this limit, you can use
png_set_user_limits(png_ptr, width_max, height_max);
to set your own limits, or use width_max = height_max = 0x7fffffffLto allow all valid dimensions (libpng may reject some very large imagesanyway because of potential buffer overflow conditions).
You should put this statement after you create the PNG structure andbefore calling png_read_info(), png_read_png(), or png_process_data().If you need to retrieve the limits that are being applied, use
width_max = png_get_user_width_max(png_ptr); height_max = png_get_user_height_max(png_ptr);
The PNG specification sets no limit on the number of ancillary chunksallowed in a PNG datastream. You can impose a limit on the total numberof sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
where 0x7fffffffL means unlimited. You can retrieve this limit with
chunk_cache_max = png_get_chunk_cache_max(png_ptr);
This limit also applies to the number of buffers that can be allocatedby png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
You can also set a limit on the amount of memory that a compressed chunkother than IDAT can occupy, with
png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
and you can retrieve the limit with
chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
Any chunks that would cause either of these limits to be exceeded willbe ignored.
.SS The high-level read interface
At this point there are two ways to proceed; through the high-levelread interface, or through a sequence of low-level read operations.You can use the high-level interface if (a) you are willing to readthe entire image into memory, and (b) the input transformationsyou want to do are limited to the following set:
PNG_TRANSFORM_IDENTITY No transformation PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to 8 bits PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit samples to bytes PNG_TRANSFORM_PACKSWAP Change order of packed pixels to LSB first PNG_TRANSFORM_EXPAND Perform set_expand() PNG_TRANSFORM_INVERT_MONO Invert monochrome images PNG_TRANSFORM_SHIFT Normalize pixels to the sBIT depth PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA to BGRA PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA to AG PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity to transparency PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples to RGB (or GA to RGBA)
(This excludes setting a background color, doing gamma transformation,quantizing, and setting filler.) If this is the case, simply do this:
png_read_png(png_ptr, info_ptr, png_transforms, NULL)
where png_transforms is an integer containing the bitwise OR of someset of transformation flags. This call is equivalent to png_read_info(),followed the set of transformations indicated by the transform mask,then png_read_image(), and finally png_read_end().
(The final parameter of this call is not yet used. Someday it might pointto transformation parameters required by some future input transform.)
You must use png_transforms and not call any png_set_transform() functionswhen you use png_read_png().
After you have called png_read_png(), you can retrieve the image datawith
row_pointers = png_get_rows(png_ptr, info_ptr);
where row_pointers is an array of pointers to the pixel data for each row:
png_bytep row_pointers[height];
If you know your image size and pixel size ahead of time, you can allocaterow_pointers prior to calling png_read_png() with
if (height > PNG_UINT_32_MAX/png_sizeof(png_byte)) png_error (png_ptr, "Image is too tall to process in memory");
if (width > PNG_UINT_32_MAX/pixel_size) png_error (png_ptr, "Image is too wide to process in memory");
row_pointers = png_malloc(png_ptr, height*png_sizeof(png_bytep));
for (int i=0; i<height, i++) row_pointers[i]=NULL; /* security precaution */
for (int i=0; i<height, i++) row_pointers[i]=png_malloc(png_ptr, width*pixel_size);
png_set_rows(png_ptr, info_ptr, &row_pointers);
Alternatively you could allocate your image in one big block and definerow_pointers[i] to point into the proper places in your block.
If you use png_set_rows(), the application is responsible for freeingrow_pointers (and row_pointers[i], if they were separately allocated).
If you don't allocate row_pointers ahead of time, png_read_png() willdo it, and it'll be free'ed by libpng when you call png_destroy_*().
.SS The low-level read interface
If you are going the low-level route, you are now ready to read allthe file information up to the actual image data. You do this with acall to png_read_info().
png_read_info(png_ptr, info_ptr);
This will process all chunks up to but not including the image data.
.SS Querying the info structure
Functions are used to get the information from the info_ptr once ithas been read. Note that these fields may not be completely filledin until png_read_end() has read the chunk data following the image.
png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, &compression_type, &filter_method);
width - holds the width of the image in pixels (up to 2^31).
height - holds the height of the image in pixels (up to 2^31).
bit_depth - holds the bit depth of one of the image channels. (valid values are 1, 2, 4, 8, 16 and depend also on the color_type. See also significant bits (sBIT) below).
color_type - describes which color/alpha channels are present. PNG_COLOR_TYPE_GRAY (bit depths 1, 2, 4, 8, 16) PNG_COLOR_TYPE_GRAY_ALPHA (bit depths 8, 16) PNG_COLOR_TYPE_PALETTE (bit depths 1, 2, 4, 8) PNG_COLOR_TYPE_RGB (bit_depths 8, 16) PNG_COLOR_TYPE_RGB_ALPHA (bit_depths 8, 16)
PNG_COLOR_MASK_PALETTE PNG_COLOR_MASK_COLOR PNG_COLOR_MASK_ALPHA
interlace_type - (PNG_INTERLACE_NONE or PNG_INTERLACE_ADAM7)
compression_type - (must be PNG_COMPRESSION_TYPE_BASE for PNG 1.0)
filter_method - (must be PNG_FILTER_TYPE_BASE for PNG 1.0, and can also be PNG_INTRAPIXEL_DIFFERENCING if the PNG datastream is embedded in a MNG-1.0 datastream)
Any or all of interlace_type, compression_type, or filter_method can be NULL if you are not interested in their values.
Note that png_get_IHDR() returns 32-bit data into the application's width and height variables. This is an unsafe situation if these are 16-bit variables. In such situations, the png_get_image_width() and png_get_image_height() functions described below are safer.
width = png_get_image_width(png_ptr, info_ptr);
height = png_get_image_height(png_ptr, info_ptr);
bit_depth = png_get_bit_depth(png_ptr, info_ptr);
color_type = png_get_color_type(png_ptr, info_ptr);
interlace_type = png_get_interlace_type(png_ptr, info_ptr);
compression_type = png_get_compression_type(png_ptr, info_ptr);
filter_method = png_get_filter_type(png_ptr, info_ptr);
channels = png_get_channels(png_ptr, info_ptr);
channels - number of channels of info for the color type (valid values are 1 (GRAY, PALETTE), 2 (GRAY_ALPHA), 3 (RGB), 4 (RGB_ALPHA or RGB + filler byte))
rowbytes = png_get_rowbytes(png_ptr, info_ptr);
rowbytes - number of bytes needed to hold a row
signature = png_get_signature(png_ptr, info_ptr);
signature - holds the signature read from the file (if any). The data is kept in the same offset it would be if the whole signature were read (i.e. if an application had already read in 4 bytes of signature before starting libpng, the remaining 4 bytes would be in signature[4] through signature[7] (see png_set_sig_bytes())).
These are also important, but their validity depends on whether the chunkhas been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) andpng_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if thedata has been read, or zero if it is missing. The parameters to thepng_get_<chunk> are set directly if they are simple data types, or apointer into the info_ptr is returned for any complex types.
png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette);
palette - the palette for the file (array of png_color)
num_palette - number of entries in the palette
png_get_gAMA(png_ptr, info_ptr, &file_gamma); png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
file_gamma - the gamma at which the file is written (PNG_INFO_gAMA)
int_file_gamma - 100,000 times the gamma at which the file is written
png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
file_srgb_intent - the rendering intent (PNG_INFO_sRGB) The presence of the sRGB chunk means that the pixel data is in the sRGB color space. This chunk also implies specific values of gAMA and cHRM.
png_get_iCCP(png_ptr, info_ptr, &name, &compression_type, &profile, &proflen);
name - The profile name.
compression_type - The compression type; always PNG_COMPRESSION_TYPE_BASE for PNG 1.0. You may give NULL to this argument to ignore it.
profile - International Color Consortium color profile data. May contain NULs.
proflen - length of profile data in bytes.
png_get_sBIT(png_ptr, info_ptr, &sig_bit);
sig_bit - the number of significant bits for (PNG_INFO_sBIT) each of the gray, red, green, and blue channels, whichever are appropriate for the given color type (png_color_16)
png_get_tRNS(png_ptr, info_ptr, &trans_alpha, &num_trans, &trans_color);
trans_alpha - array of alpha (transparency) entries for palette (PNG_INFO_tRNS)
num_trans - number of transparent entries (PNG_INFO_tRNS)
trans_color - graylevel or color sample values of the single transparent color for non-paletted images (PNG_INFO_tRNS)
png_get_hIST(png_ptr, info_ptr, &hist); (PNG_INFO_hIST)
hist - histogram of palette (array of png_uint_16)
png_get_tIME(png_ptr, info_ptr, &mod_time);
mod_time - time image was last modified (PNG_VALID_tIME)
png_get_bKGD(png_ptr, info_ptr, &background);
background - background color (PNG_VALID_bKGD) valid 16-bit red, green and blue values, regardless of color_type
num_comments = png_get_text(png_ptr, info_ptr, &text_ptr, &num_text);
num_comments - number of comments
text_ptr - array of png_text holding image comments
text_ptr[i].compression - type of compression used on "text" PNG_TEXT_COMPRESSION_NONE PNG_TEXT_COMPRESSION_zTXt PNG_ITXT_COMPRESSION_NONE PNG_ITXT_COMPRESSION_zTXt
text_ptr[i].key - keyword for comment. Must contain 1-79 characters.
text_ptr[i].text - text comments for current keyword. Can be empty.
text_ptr[i].text_length - length of text string, after decompression, 0 for iTXt
text_ptr[i].itxt_length - length of itxt string, after decompression, 0 for tEXt/zTXt
text_ptr[i].lang - language of comment (empty string for unknown).
text_ptr[i].lang_key - keyword in UTF-8 (empty string for unknown).
Note that the itxt_length, lang, and lang_key members of the text_ptr structure only exist when the library is built with iTXt chunk support.
num_text - number of comments (same as num_comments; you can put NULL here to avoid the duplication)
Note while png_set_text() will accept text, language, and translated keywords that can be NULL pointers, the structure returned by png_get_text will always contain regular zero-terminated C strings. They might be empty strings but they will never be NULL pointers.
num_spalettes = png_get_sPLT(png_ptr, info_ptr, &palette_ptr);
num_spalettes - number of sPLT chunks read.
palette_ptr - array of palette structures holding contents of one or more sPLT chunks read.
png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y, &unit_type);
offset_x - positive offset from the left edge of the screen
offset_y - positive offset from the top edge of the screen
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y, &unit_type);
res_x - pixels/unit physical resolution in x direction
res_y - pixels/unit physical resolution in x direction
unit_type - PNG_RESOLUTION_UNKNOWN, PNG_RESOLUTION_METER
png_get_sCAL(png_ptr, info_ptr, &unit, &width, &height)
unit - physical scale units (an integer)
width - width of a pixel in physical scale units
height - height of a pixel in physical scale units (width and height are doubles)
png_get_sCAL_s(png_ptr, info_ptr, &unit, &width, &height)
unit - physical scale units (an integer)
width - width of a pixel in physical scale units
height - height of a pixel in physical scale units (width and height are strings like "2.54")
num_unknown_chunks = png_get_unknown_chunks(png_ptr, info_ptr, &unknowns)
unknowns - array of png_unknown_chunk structures holding unknown chunks
unknowns[i].name - name of unknown chunk
unknowns[i].data - data of unknown chunk
unknowns[i].size - size of unknown chunk's data
unknowns[i].location - position of chunk in file
The value of "i" corresponds to the order in which the chunks were read from the PNG file or inserted with the png_set_unknown_chunks() function.
The data from the pHYs chunk can be retrieved in several convenientforms:
res_x = png_get_x_pixels_per_meter(png_ptr, info_ptr)
res_y = png_get_y_pixels_per_meter(png_ptr, info_ptr)
res_x_and_y = png_get_pixels_per_meter(png_ptr, info_ptr)
res_x = png_get_x_pixels_per_inch(png_ptr, info_ptr)
res_y = png_get_y_pixels_per_inch(png_ptr, info_ptr)
res_x_and_y = png_get_pixels_per_inch(png_ptr, info_ptr)
aspect_ratio = png_get_pixel_aspect_ratio(png_ptr, info_ptr)
Each of these returns 0 [signifying "unknown"] if the data is not present or if res_x is 0; res_x_and_y is 0 if res_x != res_y
Note that because of the way the resolutions are stored internally, the inch conversions won't come out to exactly even number. For example, 72 dpi is stored as 0.28346 pixels/meter, and when this is retrieved it is 71.9988 dpi, so be sure to round the returned value appropriately if you want to display a reasonable-looking result.
The data from the oFFs chunk can be retrieved in several convenientforms:
x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
Each of these returns 0 [signifying "unknown" if both x and y are 0] if the data is not present or if the chunk is present but the unit is the pixel. The remark about inexact inch conversions applies here as well, because a value in inches can't always be converted to microns and back without some loss of precision.
For more information, see the png_info definition in png.h and thePNG specification for chunk contents. Be careful with trustingrowbytes, as some of the transformations could increase the spaceneeded to hold a row (expand, filler, gray_to_rgb, etc.).See png_read_update_info(), below.
A quick word about text_ptr and num_text. PNG stores comments inkeyword/text pairs, one pair per chunk, with no limit on the numberof text chunks, and a 2^31 byte limit on their size. While there aresuggested keywords, there is no requirement to restrict the use to thesestrings. It is strongly suggested that keywords and text be sensibleto humans (that's the point), so don't use abbreviations. Non-printingsymbols are not allowed. See the PNG specification for more details.There is also no requirement to have text after the keyword.
Keywords should be limited to 79 Latin-1 characters without leading ortrailing spaces, but non-consecutive spaces are allowed within thekeyword. It is possible to have the same keyword any number of times.The text_ptr is an array of png_text structures, each holding apointer to a language string, a pointer to a keyword and a pointer toa text string. The text string, language code, and translatedkeyword may be empty or NULL pointers. The keyword/textpairs are put into the array in the order that they are received.However, some or all of the text chunks may be after the image, so, tomake sure you have read all the text chunks, don't mess with theseuntil after you read the stuff after the image. This will bementioned again below in the discussion that goes with png_read_end().
.SS Input transformations
After you've read the header information, you can set up the libraryto handle any special transformations of the image data. The variousways to transform the data will be described in the order that theyshould occur. This is important, as some of these change the colortype and/or bit depth of the data, and some others only work oncertain color types and bit depths. Even though each transformationchecks to see if it has data that it can do something with, you shouldmake sure to only enable a transformation if it will be valid for thedata. For example, don't swap red and blue on grayscale data.
The colors used for the background and transparency values should besupplied in the same format/depth as the current image data. Theyare stored in the same format/depth as the image data in a bKGD or tRNSchunk, so this is what libpng expects for this data. The colors aretransformed to keep in sync with the image data when an applicationcalls the png_read_update_info() routine (see below).
Data will be decoded into the supplied row buffers packed into bytesunless the library has been told to transform it into another format.For example, 4 bit/pixel paletted or grayscale data will be returned2 pixels/byte with the leftmost pixel in the high-order bits of thebyte, unless png_set_packing() is called. 8-bit RGB data will be storedin RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()is called to insert filler bytes, either before or after each RGB triplet.16-bit RGB data will be returned RRGGBB RRGGBB, with the most significantbyte of the color value first, unless png_set_strip_16() is called totransform it to regular RGB RGB triplets, or png_set_filler() orpng_set_add alpha() is called to insert filler bytes, either before orafter each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data canbe modified withpng_set_filler(), png_set_add_alpha(), or png_set_strip_16().
The following code transforms grayscale images of less than 8 to 8 bits,changes paletted images to RGB, and adds a full alpha channel if there istransparency information in a tRNS chunk. This is most useful ongrayscale images with bit depths of 2 or 4 or if there is a multiple-imageviewing application that wishes to treat all images in the same way.
if (color_type == PNG_COLOR_TYPE_PALETTE) png_set_palette_to_rgb(png_ptr);
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
The first two functions are actually aliases for png_set_expand(), addedin libpng version 1.0.4, with the function names expanded to improve codereadability. In some future version they may actually do differentthings.
As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() wasadded. It expands the sample depth without changing tRNS to alpha.
As of libpng version 1.5.2, png_set_expand_16() was added. It behaves aspng_set_expand(), however, the resultant channels have 16 bits rather than 8.Use this when the output color or gray channels are made linear to avoid fairlysevere accuracy loss.
if (bit_depth < 16) png_set_expand_16(png_ptr);
PNG can have files with 16 bits per channel. If you only can handle8 bits per channel, this will strip the pixels down to 8 bit.
if (bit_depth == 16) png_set_strip_16(png_ptr);
If, for some reason, you don't need the alpha channel on an image,and you want to remove it rather than combining it with the background(but the image author certainly had in mind that you *would* combineit with the background, so that's what you should probably do):
if (color_type & PNG_COLOR_MASK_ALPHA) png_set_strip_alpha(png_ptr);
See below for png_set_background(), which does the correct composition on asingle opaque color. This is probably what you should do in all cases ratherthan use png_set_strip_alpha() - unless you know for sure that it is the wrongthing to do.
As of libpng version 1.5.2, almost all useful expansions are supported, themajor ommissions are convertion of grayscale to indexed images (which can bedone trivially in the application) and convertion of indexed to grayscale (whichcan be done by a trivial manipulation of the palette.)
In the following table, the 01 means grayscale with depth<8, 31 meansindexed with depth<8, other numerals represent the color type, "T" meansthe tRNS chunk is present, A means an alpha channel is present, and Omeans tRNS or alpha is present but all pixels in the image are opaque.
FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O TO 01 - [G] - - - - - - - - - - - - - 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q 0 1 G + . . G G G G G G B B GB GB 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt 2 C P C C C + . . C - - CB CB B B 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt 4A lA G A T T GA GT GT GA GT GT + BA G GBA 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G 6A CA PA CA C C A T tT PA P P C CBA + BA 6O CA PBA CA C C A tT T PA P P CBA C BA +
Within the matrix, "+" identifies entries where 'from' and 'to' are the same. "-" means the transformation is not supported. "." means nothing is necessary (a tRNS chunk can just be ignored). "t" means the transformation is obtained by png_set_tRNS. "A" means the transformation is obtained by png_set_add_alpha(). "X" means the transformation is obtained by png_set_expand(). "1" means the transformation is obtained by png_set_expand_gray_1_2_4_to_8() (and by png_set_expand() if there is no transparency in the original or the final format). "C" means the transformation is obtained by png_set_gray_to_rgb(). "G" means the transformation is obtained by png_set_rgb_to_gray() or png_set_rgb_to_Y(). "P" means the transformation is obtained by png_set_expand_palette_to_rgb(). "p" means the transformation is obtained by png_set_packing(). "Q" means the transformation is obtained by png_set_quantize(). "T" means the transformation is obtained by png_set_tRNS_to_alpha(). "B" means the transformation is obtained by png_set_background(), or png_strip_alpha().
When an entry has multiple transforms listed all are required to cause theright overall transformation. When two transforms are separated by a commaeither will do the job. When transforms are enclosed in [] the transform shoulddo the job but this is currently unimplemented - a different format will resultif the suggested transformations are used.
In PNG files, the alpha channel in an imageis the level of opacity. If you need the alpha channel in an image tobe the level of transparency instead of opacity, you can invert thealpha channel (or the tRNS chunk data) after it's read, so that 0 isfully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bitimages) is fully transparent, with
png_set_invert_alpha(png_ptr);
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small asthey can, resulting in, for example, 8 pixels per byte for 1 bitfiles. This code expands to 1 pixel per byte without changing thevalues of the pixels:
if (bit_depth < 8) png_set_packing(png_ptr);
PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixelsstored in a PNG image have been "scaled" or "shifted" up to the nexthigher possible bit depth (e.g. from 5 bits/sample in the range [0,31]to 8 bits/sample in the range [0, 255]). However, it is also possibleto convert the PNG pixel data back to the original bit depth of theimage. This call reduces the pixels back down to the original bit depth:
png_color_8p sig_bit;
if (png_get_sBIT(png_ptr, info_ptr, &sig_bit)) png_set_shift(png_ptr, sig_bit);
PNG files store 3-color pixels in red, green, blue order. This codechanges the storage of the pixels to blue, green, red:
if (color_type == PNG_COLOR_TYPE_RGB || color_type == PNG_COLOR_TYPE_RGB_ALPHA) png_set_bgr(png_ptr);
PNG files store RGB pixels packed into 3 or 6 bytes. This code expands theminto 4 or 8 bytes for windowing systems that need them in this format:
if (color_type == PNG_COLOR_TYPE_RGB) png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
where "filler" is the 8 or 16-bit number to fill with, and the location iseither PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whetheryou want the filler before the RGB or after. This transformationdoes not affect images that already have full alpha channels. To add anopaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER whichwill generate RGBA pixels.
Note that png_set_filler() does not change the color type. If you wantto do that, you can add a true alpha channel with
if (color_type == PNG_COLOR_TYPE_RGB || color_type == PNG_COLOR_TYPE_GRAY) png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
where "filler" contains the alpha value to assign to each pixel.This function was added in libpng-1.2.7.
If you are reading an image with an alpha channel, and you need thedata as ARGB instead of the normal PNG format RGBA:
if (color_type == PNG_COLOR_TYPE_RGB_ALPHA) png_set_swap_alpha(png_ptr);
For some uses, you may want a grayscale image to be represented asRGB. This code will do that conversion:
if (color_type == PNG_COLOR_TYPE_GRAY || color_type == PNG_COLOR_TYPE_GRAY_ALPHA) png_set_gray_to_rgb(png_ptr);
Conversely, you can convert an RGB or RGBA image to grayscale or grayscalewith alpha.
if (color_type == PNG_COLOR_TYPE_RGB || color_type == PNG_COLOR_TYPE_RGB_ALPHA) png_set_rgb_to_gray_fixed(png_ptr, error_action, int red_weight, int green_weight);
error_action = 1: silently do the conversion
error_action = 2: issue a warning if the original image has any pixel where red != green or red != blue
error_action = 3: issue an error and abort the conversion if the original image has any pixel where red != green or red != blue
red_weight: weight of red component times 100000
green_weight: weight of green component times 100000 If either weight is negative, default weights (21268, 71514) are used.
If you have set error_action = 1 or 2, you canlater check whether the image really was gray, after processingthe image rows, with the png_get_rgb_to_gray_status(png_ptr) function.It will return a png_byte that is zero if the image was gray or1 if there were any non-gray pixels. bKGD and sBIT datawill be silently converted to grayscale, using the green channeldata, regardless of the error_action setting.
With red_weight+green_weight<=100000,the normalized graylevel is computed:
int rw = red_weight * 65536; int gw = green_weight * 65536; int bw = 65536 - (rw + gw); gray = (rw*red + gw*green + bw*blue)/65536;
The default values approximate those recommended in the CharlesPoynton's Color FAQ, <http://www.inforamp.net/~poynton/>Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
Libpng approximates this with integers scaled by 32768:
Y = (6968 * R + 23434 * G + 2366 * B)/32768
The calculation is done in a linear colorspace, if the image gammacan be determined.
If you have a grayscale and you are using png_set_expand_gray_1_2_4_to_8(),png_set_expand(), or png_set_gray_to_rgb to change to truecolor or toa higher bit-depth, you must either supply the background color as a grayvalue at the original file bit-depth (need_expand = 1) or else supply thebackground color as an RGB triplet at the final, expanded bit depth(need_expand = 0). Similarly, if you are reading a paletted image, youmust either supply the background color as a palette index (need_expand = 1)or as an RGB triplet that may or may not be in the palette (need_expand = 0).
png_color_16 my_background; png_color_16p image_background;
if (png_get_bKGD(png_ptr, info_ptr, &image_background)) png_set_background(png_ptr, image_background, PNG_BACKGROUND_GAMMA_FILE, 1, 1.0); else png_set_background(png_ptr, &my_background, PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
The png_set_background() function tells libpng to composite imageswith alpha or simple transparency against the supplied backgroundcolor. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),you may use this color, or supply another color more suitable forthe current display (e.g., the background color from a web page). Youneed to tell libpng whether the color is in the gamma space of thedisplay (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or onethat is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don'tknow why anyone would use this, but it's here).
To properly display PNG images on any kind of system, the application needsto know what the display gamma is. Ideally, the user will know this, andthe application will allow them to set it. One method of allowing the userto set the display gamma separately for each system is to check for aSCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully becorrectly set.
Note that display_gamma is the overall gamma correction required to producepleasing results, which depends on the lighting conditions in the surroundingenvironment. In a dim or brightly lit room, no compensation other thanthe physical gamma exponent of the monitor is needed, while in a dark rooma slightly smaller exponent is better.
double gamma, screen_gamma;
if (/* We have a user-defined screen gamma value */) { screen_gamma = user_defined_screen_gamma; }
/* One way that applications can share the same screen gamma value */ else if ((gamma_str = getenv("SCREEN_GAMMA")) != NULL) { screen_gamma = (double)atof(gamma_str); }
/* If we don't have another value */ else { screen_gamma = 2.2; /* A good guess for a PC monitor in a bright office or a dim room */
screen_gamma = 2.0; /* A good guess for a PC monitor in a dark room */
screen_gamma = 1.7 or 1.0; /* A good guess for Mac systems */ }
The functions png_set_gamma() and its fixed point equivalentpng_set_gamma_fixed() handle gamma transformations of the data.Pass both the file gamma and the current screen_gamma. If the file doesnot have a gamma value, you can pass one anyway if you have an idea whatit is (usually 0.45455 is a good guess for GIF images on PCs). Notethat file gammas are inverted from screen gammas. See the discussionson gamma in the PNG specification for an excellent description of whatgamma is, and why all applications should support it. It is stronglyrecommended that PNG viewers support gamma correction.
if (png_get_gAMA(png_ptr, info_ptr, &file_gamma)) png_set_gamma(png_ptr, screen_gamma, file_gamma);
else png_set_gamma(png_ptr, screen_gamma, 0.45455);
If you need to reduce an RGB file to a paletted file, or if a palettedfile has more entries then will fit on your screen, png_set_quantize()will do that. Note that this is a simple match quantization that merelyfinds the closest color available. This should work fairly well withoptimized palettes, but fairly badly with linear color cubes. If youpass a palette that is larger then maximum_colors, the file willreduce the number of colors in the palette so it will fit intomaximum_colors. If there is a histogram, it will use it to makemore intelligent choices when reducing the palette. If there is nohistogram, it may not do as good a job.
if (color_type & PNG_COLOR_MASK_COLOR) { if (png_get_valid(png_ptr, info_ptr, PNG_INFO_PLTE)) { png_uint_16p histogram = NULL;
png_get_hIST(png_ptr, info_ptr, &histogram); png_set_quantize(png_ptr, palette, num_palette, max_screen_colors, histogram, 1); }
else { png_color std_color_cube[MAX_SCREEN_COLORS] = { ... colors ... };
png_set_quantize(png_ptr, std_color_cube, MAX_SCREEN_COLORS, MAX_SCREEN_COLORS, NULL,0); } }
PNG files describe monochrome as black being zero and white being one.The following code will reverse this (make black be one and white bezero):
if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY) png_set_invert_mono(png_ptr);
This function can also be used to invert grayscale and gray-alpha images:
if (color_type == PNG_COLOR_TYPE_GRAY || color_type == PNG_COLOR_TYPE_GRAY_ALPHA) png_set_invert_mono(png_ptr);
PNG files store 16 bit pixels in network byte order (big-endian,ie. most significant bits first). This code changes the storage to theother way (little-endian, i.e. least significant bits first, theway PCs store them):
if (bit_depth == 16) png_set_swap(png_ptr);
If you are using packed-pixel images (1, 2, or 4 bits/pixel), and youneed to change the order the pixels are packed into bytes, you can use:
if (bit_depth < 8) png_set_packswap(png_ptr);
Finally, you can write your own transformation function if none ofthe existing ones meets your needs. This is done by setting a callbackwith
png_set_read_user_transform_fn(png_ptr, read_transform_fn);
You must supply the function
void read_transform_fn(png_structp png_ptr, png_row_infop row_info, png_bytep data)
See pngtest.c for a working example. Your function will be calledafter all of the other transformations have been processed. Take care withinterlaced images if you do the interlace yourself - the width of the row is thewidth in 'row_info', not the overall image width.
If supported libpng provides two information routines that you can use to findwhere you are in processing the image:
png_get_current_pass_number(png_structp png_ptr); png_get_current_row_number(png_structp png_ptr);
Don't try using these outside a transform callback - firstly they are onlysupported if user transforms are supported, secondly they may well returnunexpected results unless the row is actually being processed at the moment theyare called.
With interlacedimages the value returned is the row in the input sub-image image. UsePNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) tofind the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
The discussion of interlace handling above contains more information on how touse these values.
You can also set up a pointer to a user structure for use by yourcallback function, and you can inform libpng that your transformfunction will change the number of channels or bit depth with thefunction
png_set_user_transform_info(png_ptr, user_ptr, user_depth, user_channels);
The user's application, not libpng, is responsible for allocating andfreeing any memory required for the user structure.
You can retrieve the pointer via the functionpng_get_user_transform_ptr(). For example:
voidp read_user_transform_ptr = png_get_user_transform_ptr(png_ptr);
The last thing to handle is interlacing; this is covered in detail below,but you must call the function here if you want libpng to handle expansionof the interlaced image.
number_of_passes = png_set_interlace_handling(png_ptr);
After setting the transformations, libpng can update your png_infostructure to reflect any transformations you've requested with thiscall. This is most useful to update the info structure's rowbytesfield so you can use it to allocate your image memory. This functionwill also update your palette with the correct screen_gamma andbackground if these have been given with the calls above.
png_read_update_info(png_ptr, info_ptr);
After you call png_read_update_info(), you can allocate anymemory you need to hold the image. The row data is simplyraw byte data for all forms of images. As the actual allocationvaries among applications, no example will be given. If youare allocating one large chunk, you will need to build anarray of pointers to each row, as it will be needed for someof the functions below.
Remember: Before you call png_read_update_info(), the png_get_functions return the values corresponding to the original PNG image.After you call png_read_update_info the values refer to the imagethat libpng will output. Consequently you must call all the png_set_functions before you call png_read_update_info(). This is particularlyimportant for png_set_interlace_handling() - if you are going to callpng_read_update_info() you must call png_set_interlace_handling() beforeit unless you want to receive interlaced output.
.SS Reading image data
After you've allocated memory, you can read the image data.The simplest way to do this is in one function call. If you areallocating enough memory to hold the whole image, you can justcall png_read_image() and libpng will read in all the image dataand put it in the memory area supplied. You will need to pass inan array of pointers to each row.
This function automatically handles interlacing, so you don'tneed to call png_set_interlace_handling() (unless you callpng_read_update_info()) or call this function multiple times, or anyof that other stuff necessary with png_read_rows().
png_read_image(png_ptr, row_pointers);
where row_pointers is:
png_bytep row_pointers[height];
You can point to void or char or whatever you use for pixels.
If you don't want to read in the whole image at once, you canuse png_read_rows() instead. If there is no interlacing (checkinterlace_type == PNG_INTERLACE_NONE), this is simple:
png_read_rows(png_ptr, row_pointers, NULL, number_of_rows);
where row_pointers is the same as in the png_read_image() call.
If you are doing this just one row at a time, you can do this witha single row_pointer instead of an array of row_pointers:
png_bytep row_pointer = row; png_read_row(png_ptr, row_pointer, NULL);
If the file is interlaced (interlace_type != 0 in the IHDR chunk), thingsget somewhat harder. The only current (PNG Specification version 1.2)interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);a somewhat complicated 2D interlace scheme, known as Adam7, thatbreaks down an image into seven smaller images of varying size, basedon an 8x8 grid. This number is defined (from libpng 1.5) asPNG_INTERLACE_ADAM7_PASSES in png.h
libpng can fill out those images or it can give them to you "as is".It is almost always better to have libpng handle the interlacing for you.If you want the images filled out, there are two ways to do that. The onementioned in the PNG specification is to expand each pixel to coverthose pixels that have not been read yet (the "rectangle" method).This results in a blocky image for the first pass, which graduallysmooths out as more pixels are read. The other method is the "sparkle"method, where pixels are drawn only in their final locations, with therest of the image remaining whatever colors they were initialized tobefore the start of the read. The first method usually looks better,but tends to be slower, as there are more pixels to put in the rows.
If, as is likely, you want libpng to expand the images, call this beforecalling png_start_read_image() or png_read_update_info():
if (interlace_type == PNG_INTERLACE_ADAM7) number_of_passes = png_set_interlace_handling(png_ptr);
This will return the number of passes needed. Currently, this is seven,but may change if another interlace type is added. This function can becalled even if the file is not interlaced, where it will return one pass.You then need to read the whole image 'number_of_passes' times. Each timewill distribute the pixels from the current pass to the correct place inthe output image, so you need to supply the same rows to png_read_rows ineach pass.
If you are not going to display the image after each pass, but aregoing to wait until the entire image is read in, use the sparkleeffect. This effect is faster and the end result of either methodis exactly the same. If you are planning on displaying the imageafter each pass, the "rectangle" effect is generally considered thebetter looking one.
If you only want the "sparkle" effect, just call png_read_rows() asnormal, with the third parameter NULL. Make sure you make pass overthe image number_of_passes times, and you don't change the data in therows between calls. You can change the locations of the data, justnot the data. Each pass only writes the pixels appropriate for thatpass, and assumes the data from previous passes is still valid.
png_read_rows(png_ptr, row_pointers, NULL, number_of_rows);
If you only want the first effect (the rectangles), do the same asbefore except pass the row buffer in the third parameter, and leavethe second parameter NULL.
png_read_rows(png_ptr, NULL, row_pointers, number_of_rows);
If you don't want libpng to handle the interlacing details, just callpng_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.Each of the images is a valid image by itself, however you will almostcertainly need to distribute the pixels from each sub-image to thecorrect place. This is where everything gets very tricky.
If you want to retrieve the separate images you must pass the correctnumber of rows to each successive call of png_read_rows(). The calculationgets pretty complicated for small images, where some sub-images maynot even exist because either their width or height ends up zero.libpng provides two macros to help you in 1.5 and later versions:
png_uint_32 width = PNG_PASS_COLS(image_width, pass_number); png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
Respectively these tell you the width and height of the sub-imagecorresponding to the numbered pass. 'pass' is in in the range 0 to 6 -this can be confusing because the specification refers to the same passesas 1 to 7! Be careful, you must check both the width and height beforecalling png_read_rows() and not call it for that pass if either is zero.
You can, of course, read each sub-image row by row. If you want toproduce optimal code to make a pixel-by-pixel transformation of aninterlaced image this is the best approach; read each row of each pass,transform it, and write it out to a new interlaced image.
If you want to de-interlace the image yourself libpng provides furthermacros to help that tell you where to place the pixels in the output image.Because the interlacing scheme is rectangular - sub-image pixels are alwaysarranged on a rectangular grid - all you need to know for each pass is thestarting column and row in the output image of the first pixel plus thespacing between each pixel. As of libpng 1.5 there are four macros toretrieve this information:
png_uint_32 x = PNG_PASS_START_COL(pass); png_uint_32 y = PNG_PASS_START_ROW(pass); png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass); png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
These allow you to write the obvious loop:
png_uint_32 input_y = 0; png_uint_32 output_y = PNG_PASS_START_ROW(pass);
while (output_y < output_image_height) { png_uint_32 input_x = 0; png_uint_32 output_x = PNG_PASS_START_COL(pass);
while (output_x < output_image_width) { image[output_y][output_x] = subimage[pass][input_y][input_x++];
output_x += xStep; }
++input_y; output_y += yStep; }
Notice that the steps between successive output rows and columns arereturned as shifts. This is possible because the pixels in the subimagesare always a power of 2 apart - 1, 2, 4 or 8 pixels - in the originalimage. In practice you may need to directly calculate the output coordinategiven an input coordinate. libpng provides two further macros for thispurpose:
png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass); png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
Finally a pair of macros are provided to tell you if a particular imagerow or column appears in a given pass:
int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass); int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
Bear in mind that you will probably also need to check the width and heightof the pass in addition to the above to be sure the pass even exists!
With any luck you are convinced by now that you don't want to do your owninterlace handling. In reality normally the only good reason for doing thisis if you are processing PNG files on a pixel-by-pixel basis and don't wantto load the whole file into memory when it is interlaced.
libpng includes a test program, pngvalid, that illustrates reading andwriting of interlaced images. If you can't get interlacing to work in yourcode and don't want to leave it to libpng (the recommended approach) seehow pngvalid.c does it.
.SS Finishing a sequential read
After you are finished reading the image through thelow-level interface, you can finish reading the file. If you areinterested in comments or time, which may be stored either before orafter the image data, you should pass the separate png_info struct ifyou want to keep the comments from before and after the imageseparate. If you are not interested, you can pass NULL.
png_read_end(png_ptr, end_info);
When you are done, you can free all memory allocated by libpng like this:
png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
It is also possible to individually free the info_ptr members thatpoint to libpng-allocated storage with the following function:
png_free_data(png_ptr, info_ptr, mask, seq)
mask - identifies data to be freed, a mask containing the bitwise OR of one or more of PNG_FREE_PLTE, PNG_FREE_TRNS, PNG_FREE_HIST, PNG_FREE_ICCP, PNG_FREE_PCAL, PNG_FREE_ROWS, PNG_FREE_SCAL, PNG_FREE_SPLT, PNG_FREE_TEXT, PNG_FREE_UNKN, or simply PNG_FREE_ALL
seq - sequence number of item to be freed (-1 for all items)
This function may be safely called when the relevant storage hasalready been freed, or has not yet been allocated, or was allocatedby the user and not by libpng, and will in those cases do nothing.The "seq" parameter is ignored if only one item of the selected datatype, such as PLTE, is allowed. If "seq" is not -1, and multiple itemsare allowed for the data type identified in the mask, such as text orsPLT, only the n'th item in the structure is freed, where n is "seq".
The default behavior is only to free data that was allocated internallyby libpng. This can be changed, so that libpng will not free the data,or so that it will free data that was allocated by the user with png_malloc()or png_zalloc() and passed in via a png_set_*() function, with
png_data_freer(png_ptr, info_ptr, freer, mask)
freer - one of PNG_DESTROY_WILL_FREE_DATA PNG_SET_WILL_FREE_DATA PNG_USER_WILL_FREE_DATA
mask - which data elements are affected same choices as in png_free_data()
This function only affects data that has already been allocated.You can call this function after reading the PNG data but before callingany png_set_*() functions, to control whether the user or the png_set_*()function is responsible for freeing any existing data that might be present,and again after the png_set_*() functions to control whether the useror png_destroy_*() is supposed to free the data. When the user assumesresponsibility for libpng-allocated data, the application must usepng_free() to free it, and when the user transfers responsibility to libpngfor data that the user has allocated, the user must have used png_malloc()or png_zalloc() to allocate it.
If you allocated your row_pointers in a single block, as suggested above inthe description of the high level read interface, you must not transferresponsibility for freeing it to the png_set_rows or png_read_destroy function,because they would also try to free the individual row_pointers[i].
If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keywordseparately, do not transfer responsibility for freeing text_ptr to libpng,because when libpng fills a png_text structure it combines these members withthe key member, and png_free_data() will free only text_ptr.key. Similarly,if you transfer responsibility for free'ing text_ptr from libpng to yourapplication, your application must not separately free those members.
The png_free_data() function will turn off the "valid" flag for anythingit frees. If you need to turn the flag off for a chunk that was freed byyour application instead of by libpng, you can use
png_set_invalid(png_ptr, info_ptr, mask);
mask - identifies the chunks to be made invalid, containing the bitwise OR of one or more of PNG_INFO_gAMA, PNG_INFO_sBIT, PNG_INFO_cHRM, PNG_INFO_PLTE, PNG_INFO_tRNS, PNG_INFO_bKGD, PNG_INFO_hIST, PNG_INFO_pHYs, PNG_INFO_oFFs, PNG_INFO_tIME, PNG_INFO_pCAL, PNG_INFO_sRGB, PNG_INFO_iCCP, PNG_INFO_sPLT, PNG_INFO_sCAL, PNG_INFO_IDAT
For a more compact example of reading a PNG image, see the file example.c.
.SS Reading PNG files progressively
The progressive reader is slightly different then the non-progressivereader. Instead of calling png_read_info(), png_read_rows(), andpng_read_end(), you make one call to png_process_data(), which callscallbacks when it has the info, a row, or the end of the image. Youset up these callbacks with png_set_progressive_read_fn(). You don'thave to worry about the input/output functions of libpng, as you aregiving the library the data directly in png_process_data(). I willassume that you have read the section on reading PNG files above,so I will only highlight the differences (although I will showall of the code).
png_structp png_ptr;png_infop info_ptr;
/* An example code fragment of how you would initialize the progressive reader in your application. */ int initialize_png_reader() { png_ptr = png_create_read_struct (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, user_error_fn, user_warning_fn);
if (!png_ptr) return (ERROR);
info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr) { png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL); return (ERROR); }
if (setjmp(png_jmpbuf(png_ptr))) { png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL); return (ERROR); }
/* This one's new. You can provide functions to be called when the header info is valid, when each row is completed, and when the image is finished. If you aren't using all functions, you can specify NULL parameters. Even when all three functions are NULL, you need to call png_set_progressive_read_fn(). You can use any struct as the user_ptr (cast to a void pointer for the function call), and retrieve the pointer from inside the callbacks using the function
png_get_progressive_ptr(png_ptr);
which will return a void pointer, which you have to cast appropriately. */ png_set_progressive_read_fn(png_ptr, (void *)user_ptr, info_callback, row_callback, end_callback);
return 0; }
/* A code fragment that you call as you receive blocks of data */ int process_data(png_bytep buffer, png_uint_32 length) { if (setjmp(png_jmpbuf(png_ptr))) { png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL); return (ERROR); }
/* This one's new also. Simply give it a chunk of data from the file stream (in order, of course). On machines with segmented memory models machines, don't give it any more than 64K. The library seems to run fine with sizes of 4K. Although you can give it much less if necessary (I assume you can give it chunks of 1 byte, I haven't tried less then 256 bytes yet). When this function returns, you may want to display any rows that were generated in the row callback if you don't already do so there. */ png_process_data(png_ptr, info_ptr, buffer, length);
/* At this point you can call png_process_data_skip if you want to handle data the library will skip yourself; it simply returns the number of bytes to skip (and stops libpng skipping that number of bytes on the next png_process_data call). return 0; }
/* This function is called (as set by png_set_progressive_read_fn() above) when enough data has been supplied so all of the header has been read. */ void info_callback(png_structp png_ptr, png_infop info) { /* Do any setup here, including setting any of the transformations mentioned in the Reading PNG files section. For now, you _must_ call either png_start_read_image() or png_read_update_info() after all the transformations are set (even if you don't set any). You may start getting rows before png_process_data() returns, so this is your last chance to prepare for that.
This is where you turn on interlace handling, assuming you don't want to do it yourself.
If you need to you can stop the processing of your original input data at this point by calling png_process_data_pause. This returns the number of unprocessed bytes from the last png_process_data call - it is up to you to ensure that the next call sees these bytes again. If you don't want to bother with this you can get libpng to cache the unread bytes by setting the 'save' parameter (see png.h) but then libpng will have to copy the data internally. */ }
/* This function is called when each row of image data is complete */ void row_callback(png_structp png_ptr, png_bytep new_row, png_uint_32 row_num, int pass) { /* If the image is interlaced, and you turned on the interlace handler, this function will be called for every row in every pass. Some of these rows will not be changed from the previous pass. When the row is not changed, the new_row variable will be NULL. The rows and passes are called in order, so you don't really need the row_num and pass, but I'm supplying them because it may make your life easier.
If you did not turn on interlace handling then the callback is called for each row of each sub-image when the image is interlaced. In this case 'row_num' is the row in the sub-image, not the row in the output image as it is in all other cases.
For the non-NULL rows of interlaced images when you have switched on libpng interlace handling, you must call png_progressive_combine_row() passing in the row and the old row. You can call this function for NULL rows (it will just return) and for non-interlaced images (it just does the memcpy for you) if it will make the code easier. Thus, you can just do this for all cases if you switch on interlace handling; */
png_progressive_combine_row(png_ptr, old_row, new_row);
/* where old_row is what was displayed for previously for the row. Note that the first pass (pass == 0, really) will completely cover the old row, so the rows do not have to be initialized. After the first pass (and only for interlaced images), you will have to pass the current row, and the function will combine the old row and the new row.
You can also call png_process_data_pause in this callback - see above. */ }
void end_callback(png_structp png_ptr, png_infop info) { /* This function is called after the whole image has been read, including any chunks after the image (up to and including the IEND). You will usually have the same info chunk as you had in the header, although some data may have been added to the comments and time fields.
Most people won't do much here, perhaps setting a flag that marks the image as finished. */ }
.SH IV. Writing
Much of this is very similar to reading. However, everything ofimportance is repeated here, so you won't have to constantly lookback up in the reading section to understand writing.
.SS Setup
You will want to do the I/O initialization before you get into libpng,so if it doesn't work, you don't have anything to undo. If you are notusing the standard I/O functions, you will need to replace them withcustom writing functions. See the discussion under Customizing libpng.
FILE *fp = fopen(file_name, "wb");
if (!fp) return (ERROR);
Next, png_struct and png_info need to be allocated and initialized.As these can be both relatively large, you may not want to store theseon the stack, unless you have stack space to spare. Of course, youwill want to check if they return NULL. If you are also reading,you won't want to name your read structure and your write structureboth "png_ptr"; you can call them anything you like, such as"read_ptr" and "write_ptr". Look at pngtest.c, for example.
png_structp png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, user_error_fn, user_warning_fn);
if (!png_ptr) return (ERROR);
png_infop info_ptr = png_create_info_struct(png_ptr); if (!info_ptr) { png_destroy_write_struct(&png_ptr, (png_infopp)NULL); return (ERROR); }
If you want to use your own memory allocation routines,define PNG_USER_MEM_SUPPORTED and usepng_create_write_struct_2() instead of png_create_write_struct():
png_structp png_ptr = png_create_write_struct_2 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, user_error_fn, user_warning_fn, (png_voidp) user_mem_ptr, user_malloc_fn, user_free_fn);
After you have these structures, you will need to set up theerror handling. When libpng encounters an error, it expects tolongjmp() back to your routine. Therefore, you will need to callsetjmp() and pass the png_jmpbuf(png_ptr). If youwrite the file from different routines, you will need to updatethe png_jmpbuf(png_ptr) every time you enter a new routine that willcall a png_*() function. See your documentation of setjmp/longjmpfor your compiler for more information on setjmp/longjmp. Seethe discussion on libpng error handling in the Customizing Libpngsection below for more information on the libpng error handling.
if (setjmp(png_jmpbuf(png_ptr))) { png_destroy_write_struct(&png_ptr, &info_ptr); fclose(fp); return (ERROR); } ... return;
If you would rather avoid the complexity of setjmp/longjmp issues,you can compile libpng with PNG_NO_SETJMP, in which caseerrors will result in a call to PNG_ABORT() which defaults to abort().
You can #define PNG_ABORT() to a function that does somethingmore useful than abort(), as long as your function does notreturn.
Now you need to set up the output code. The default for libpng is touse the C function fwrite(). If you use this, you will need to pass avalid FILE * in the function png_init_io(). Be sure that the file isopened in binary mode. Again, if you wish to handle writing data inanother way, see the discussion on libpng I/O handling in the CustomizingLibpng section below.
png_init_io(png_ptr, fp);
If you are embedding your PNG into a datastream such as MNG, and don'twant libpng to write the 8-byte signature, or if you have alreadywritten the signature in your application, use
png_set_sig_bytes(png_ptr, 8);
to inform libpng that it should not write a signature.
.SS Write callbacks
At this point, you can set up a callback function that will becalled after each row has been written, which you can use to controla progress meter or the like. It's demonstrated in pngtest.c.You must supply a function
void write_row_callback(png_structp png_ptr, png_uint_32 row, int pass); { /* put your code here */ }
(You can give it another name that you like instead of "write_row_callback")
To inform libpng about your function, use
png_set_write_status_fn(png_ptr, write_row_callback);
When this function is called the row has already been completely processed andit has also been written out. The 'row' and 'pass' refer to the next row to behandled. For thenon-interlaced case the row that was just handled is simply one less than thepassed in row number, and pass will always be 0. For the interlaced case thesame applies unless the row value is 0, in which case the row just handled wasthe last one from one of the preceding passes. Because interlacing may skip apass you cannot be sure that the preceding pass is just 'pass-1', if you reallyneed to know what the last pass is record (row,pass) from the callback and usethe last recorded value each time.
As with the user transform you can find the output row using thePNG_ROW_FROM_PASS_ROW macro.
You now have the option of modifying how the compression library willrun. The following functions are mainly for testing, but may be usefulin some cases, like if you need to write PNG files extremely fast andare willing to give up some compression, or if you want to get themaximum possible compression at the expense of slower writing. If youhave no special needs in this area, let the library do what it wants bynot calling this function at all, as it has been tuned to deliver a goodspeed/compression ratio. The second parameter to png_set_filter() isthe filter method, for which the only valid values are 0 (as of theJuly 1999 PNG specification, version 1.2) or 64 (if you are writinga PNG datastream that is to be embedded in a MNG datastream). The thirdparameter is a flag that indicates which filter type(s) are to be testedfor each scanline. See the PNG specification for details on the specificfilter types.
/* turn on or off filtering, and/or choose specific filters. You can use either a single PNG_FILTER_VALUE_NAME or the bitwise OR of one or more PNG_FILTER_NAME masks. */ png_set_filter(png_ptr, 0, PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE | PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB | PNG_FILTER_UP | PNG_FILTER_VALUE_UP | PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG | PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH| PNG_ALL_FILTERS);
If an application wants to start and stop using particular filters duringcompression, it should start out with all of the filters (to ensure thatthe previous row of pixels will be stored in case it's needed later),and then add and remove them after the start of compression.
If you are writing a PNG datastream that is to be embedded in a MNGdatastream, the second parameter can be either 0 or 64.
The png_set_compression_*() functions interface to the zlib compressionlibrary, and should mostly be ignored unless you really know what you aredoing. The only generally useful call is png_set_compression_level()which changes how much time zlib spends on trying to compress the imagedata. See the Compression Library (zlib.h and algorithm.txt, distributedwith zlib) for details on the compression levels.
#include zlib.h
/* set the zlib compression level */ png_set_compression_level(png_ptr, Z_BEST_COMPRESSION);
/* set other zlib parameters */ png_set_compression_mem_level(png_ptr, 8); png_set_compression_strategy(png_ptr, Z_DEFAULT_STRATEGY); png_set_compression_window_bits(png_ptr, 15); png_set_compression_method(png_ptr, 8); png_set_compression_buffer_size(png_ptr, 8192)
extern PNG_EXPORT(void,png_set_zbuf_size)
.SS Setting the contents of info for output
You now need to fill in the png_info structure with all the data youwish to write before the actual image. Note that the only thing youare allowed to write after the image is the text chunks and the timechunk (as of PNG Specification 1.2, anyway). See png_write_end() andthe latest PNG specification for more information on that. If youwish to write them before the image, fill them in now, and flag thatdata as being valid. If you want to wait until after the data, don'tfill them until png_write_end(). For all the fields in png_info andtheir data types, see png.h. For explanations of what the fieldscontain, see the PNG specification.
Some of the more important parts of the png_info are:
png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, color_type, interlace_type, compression_type, filter_method)
width - holds the width of the image in pixels (up to 2^31).
height - holds the height of the image in pixels (up to 2^31).
bit_depth - holds the bit depth of one of the image channels. (valid values are 1, 2, 4, 8, 16 and depend also on the color_type. See also significant bits (sBIT) below).
color_type - describes which color/alpha channels are present. PNG_COLOR_TYPE_GRAY (bit depths 1, 2, 4, 8, 16) PNG_COLOR_TYPE_GRAY_ALPHA (bit depths 8, 16) PNG_COLOR_TYPE_PALETTE (bit depths 1, 2, 4, 8) PNG_COLOR_TYPE_RGB (bit_depths 8, 16) PNG_COLOR_TYPE_RGB_ALPHA (bit_depths 8, 16)
PNG_COLOR_MASK_PALETTE PNG_COLOR_MASK_COLOR PNG_COLOR_MASK_ALPHA
interlace_type - PNG_INTERLACE_NONE or PNG_INTERLACE_ADAM7
compression_type - (must be PNG_COMPRESSION_TYPE_DEFAULT)
filter_method - (must be PNG_FILTER_TYPE_DEFAULT or, if you are writing a PNG to be embedded in a MNG datastream, can also be PNG_INTRAPIXEL_DIFFERENCING)
If you call png_set_IHDR(), the call must appear before any of theother png_set_*() functions, because they might require access to some ofthe IHDR settings. The remaining png_set_*() functions can be calledin any order.
If you wish, you can reset the compression_type, interlace_type, orfilter_method later by calling png_set_IHDR() again; if you do this, thewidth, height, bit_depth, and color_type must be the same in each call.
png_set_PLTE(png_ptr, info_ptr, palette, num_palette);
palette - the palette for the file (array of png_color) num_palette - number of entries in the palette
png_set_gAMA(png_ptr, info_ptr, file_gamma); png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
file_gamma - the gamma at which the image was created (PNG_INFO_gAMA)
int_file_gamma - 100,000 times the gamma at which the image was created
png_set_sRGB(png_ptr, info_ptr, srgb_intent);
srgb_intent - the rendering intent (PNG_INFO_sRGB) The presence of the sRGB chunk means that the pixel data is in the sRGB color space. This chunk also implies specific values of gAMA and cHRM. Rendering intent is the CSS-1 property that has been defined by the International Color Consortium (http://www.color.org). It can be one of PNG_sRGB_INTENT_SATURATION, PNG_sRGB_INTENT_PERCEPTUAL, PNG_sRGB_INTENT_ABSOLUTE, or PNG_sRGB_INTENT_RELATIVE.
png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr, srgb_intent);
srgb_intent - the rendering intent (PNG_INFO_sRGB) The presence of the sRGB chunk means that the pixel data is in the sRGB color space. This function also causes gAMA and cHRM chunks with the specific values that are consistent with sRGB to be written.
png_set_iCCP(png_ptr, info_ptr, name, compression_type, profile, proflen);
name - The profile name.
compression_type - The compression type; always PNG_COMPRESSION_TYPE_BASE for PNG 1.0. You may give NULL to this argument to ignore it.
profile - International Color Consortium color profile data. May contain NULs.
proflen - length of profile data in bytes.
png_set_sBIT(png_ptr, info_ptr, sig_bit);
sig_bit - the number of significant bits for (PNG_INFO_sBIT) each of the gray, red, green, and blue channels, whichever are appropriate for the given color type (png_color_16)
png_set_tRNS(png_ptr, info_ptr, trans_alpha, num_trans, trans_color);
trans_alpha - array of alpha (transparency) entries for palette (PNG_INFO_tRNS)
trans_color - graylevel or color sample values (in order red, green, blue) of the single transparent color for non-paletted images (PNG_INFO_tRNS)
num_trans - number of transparent entries (PNG_INFO_tRNS)
png_set_hIST(png_ptr, info_ptr, hist);
hist - histogram of palette (array of png_uint_16) (PNG_INFO_hIST)
png_set_tIME(png_ptr, info_ptr, mod_time);
mod_time - time image was last modified (PNG_VALID_tIME)
png_set_bKGD(png_ptr, info_ptr, background);
background - background color (PNG_VALID_bKGD)
png_set_text(png_ptr, info_ptr, text_ptr, num_text);
text_ptr - array of png_text holding image comments
text_ptr[i].compression - type of compression used on "text" PNG_TEXT_COMPRESSION_NONE PNG_TEXT_COMPRESSION_zTXt PNG_ITXT_COMPRESSION_NONE PNG_ITXT_COMPRESSION_zTXt text_ptr[i].key - keyword for comment. Must contain 1-79 characters. text_ptr[i].text - text comments for current keyword. Can be NULL or empty. text_ptr[i].text_length - length of text string, after decompression, 0 for iTXt text_ptr[i].itxt_length - length of itxt string, after decompression, 0 for tEXt/zTXt text_ptr[i].lang - language of comment (NULL or empty for unknown). text_ptr[i].translated_keyword - keyword in UTF-8 (NULL or empty for unknown). Note that the itxt_length, lang, and lang_key members of the text_ptr structure only exist when the library is built with iTXt chunk support.
num_text - number of comments
png_set_sPLT(png_ptr, info_ptr, &palette_ptr, num_spalettes);
palette_ptr - array of png_sPLT_struct structures to be added to the list of palettes in the info structure. num_spalettes - number of palette structures to be added.
png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y, unit_type);
offset_x - positive offset from the left edge of the screen
offset_y - positive offset from the top edge of the screen
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
png_set_pHYs(png_ptr, info_ptr, res_x, res_y, unit_type);
res_x - pixels/unit physical resolution in x direction
res_y - pixels/unit physical resolution in y direction
unit_type - PNG_RESOLUTION_UNKNOWN, PNG_RESOLUTION_METER
png_set_sCAL(png_ptr, info_ptr, unit, width, height)
unit - physical scale units (an integer)
width - width of a pixel in physical scale units
height - height of a pixel in physical scale units (width and height are doubles)
png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
unit - physical scale units (an integer)
width - width of a pixel in physical scale units
height - height of a pixel in physical scale units (width and height are strings like "2.54")
png_set_unknown_chunks(png_ptr, info_ptr, &unknowns, num_unknowns)
unknowns - array of png_unknown_chunk structures holding unknown chunks unknowns[i].name - name of unknown chunk unknowns[i].data - data of unknown chunk unknowns[i].size - size of unknown chunk's data unknowns[i].location - position to write chunk in file 0: do not write chunk PNG_HAVE_IHDR: before PLTE PNG_HAVE_PLTE: before IDAT PNG_AFTER_IDAT: after IDAT
The "location" member is set automatically according towhat part of the output file has already been written.You can change its value after calling png_set_unknown_chunks()as demonstrated in pngtest.c. Within each of the "locations",the chunks are sequenced according to their position in thestructure (that is, the value of "i", which is the order in whichthe chunk was either read from the input file or defined withpng_set_unknown_chunks).
A quick word about text and num_text. text is an array of png_textstructures. num_text is the number of valid structures in the array.Each png_text structure holds a language code, a keyword, a text value,and a compression type.
The compression types have the same valid numbers as the compressiontypes of the image data. Currently, the only valid number is zero.However, you can store text either compressed or uncompressed, unlikeimages, which always have to be compressed. So if you don't want thetext compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.Because tEXt and zTXt chunks don't have a language field, if youspecify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXtany language code or translated keyword will not be written out.
Until text gets around 1000 bytes, it is not worth compressing it.After the text has been written out to the file, the compression typeis set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,so that it isn't written out again at the end (in case you are callingpng_write_end() with the same struct).
The keywords that are given in the PNG Specification are:
Title Short (one line) title or caption for image
Author Name of image's creator
Description Description of image (possibly long)
Copyright Copyright notice
Creation Time Time of original image creation (usually RFC 1123 format, see below)
Software Software used to create the image
Disclaimer Legal disclaimer
Warning Warning of nature of content
Source Device used to create the image
Comment Miscellaneous comment; conversion from other image format
The keyword-text pairs work like this. Keywords should be shortsimple descriptions of what the comment is about. Some typicalkeywords are found in the PNG specification, as is some recommendationson keywords. You can repeat keywords in a file. You can even writesome text before the image and some after. For example, you may wantto put a description of the image before the image, but leave thedisclaimer until after, so viewers working over modem connectionsdon't have to wait for the disclaimer to go over the modem beforethey start seeing the image. Finally, keywords should be fullwords, not abbreviations. Keywords and text are in the ISO 8859-1(Latin-1) character set (a superset of regular ASCII) and can notcontain NUL characters, and should not contain control or otherunprintable characters. To make the comments widely readable, stickwith basic ASCII, and avoid machine specific character set extensionslike the IBM-PC character set. The keyword must be present, butyou can leave off the text string on non-compressed pairs.Compressed pairs must have a text string, as only the text stringis compressed anyway, so the compression would be meaningless.
PNG supports modification time via the png_time structure. Twoconversion routines are provided, png_convert_from_time_t() fortime_t and png_convert_from_struct_tm() for struct tm. Thetime_t routine uses gmtime(). You don't have to use either ofthese, but if you wish to fill in the png_time structure directly,you should provide the time in universal time (GMT) if possibleinstead of your local time. Note that the year number is the fullyear (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), andthat months start with 1.
If you want to store the time of the original image creation, you shoulduse a plain tEXt chunk with the "Creation Time" keyword. This isnecessary because the "creation time" of a PNG image is somewhat vague,depending on whether you mean the PNG file, the time the image wascreated in a non-PNG format, a still photo from which the image wasscanned, or possibly the subject matter itself. In order to facilitatemachine-readable dates, it is recommended that the "Creation Time"tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),although this isn't a requirement. Unlike the tIME chunk, the"Creation Time" tEXt chunk is not expected to be automatically changedby the software. To facilitate the use of RFC 1123 dates, a functionpng_convert_to_rfc1123(png_timep) is provided to convert from PNGtime to an RFC 1123 format string.
.SS Writing unknown chunks
You can use the png_set_unknown_chunks function to queue up chunksfor writing. You give it a chunk name, raw data, and a size; that'sall there is to it. The chunks will be written by the next followingpng_write_info_before_PLTE, png_write_info, or png_write_end function.Any chunks previously read into the info structure's unknown-chunklist will also be written out in a sequence that satisfies the PNGspecification's ordering rules.
.SS The high-level write interface
At this point there are two ways to proceed; through the high-levelwrite interface, or through a sequence of low-level write operations.You can use the high-level interface if your image data is presentin the info structure. All defined outputtransformations are permitted, enabled by the following masks.
PNG_TRANSFORM_IDENTITY No transformation PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples PNG_TRANSFORM_PACKSWAP Change order of packed pixels to LSB first PNG_TRANSFORM_INVERT_MONO Invert monochrome images PNG_TRANSFORM_SHIFT Normalize pixels to the sBIT depth PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA to BGRA PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA to AG PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity to transparency PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes (deprecated). PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading filler bytes PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing filler bytes
If you have valid image data in the info structure (you can usepng_set_rows() to put image data in the info structure), simply do this:
png_write_png(png_ptr, info_ptr, png_transforms, NULL)
where png_transforms is an integer containing the bitwise OR of some set oftransformation flags. This call is equivalent to png_write_info(),followed the set of transformations indicated by the transform mask,then png_write_image(), and finally png_write_end().
(The final parameter of this call is not yet used. Someday it might pointto transformation parameters required by some future output transform.)
You must use png_transforms and not call any png_set_transform() functionswhen you use png_write_png().
.SS The low-level write interface
If you are going the low-level route instead, you are now ready towrite all the file information up to the actual image data. You dothis with a call to png_write_info().
png_write_info(png_ptr, info_ptr);
Note that there is one transformation you may need to do beforepng_write_info(). In PNG files, the alpha channel in an image is thelevel of opacity. If your data is supplied as a level of transparency,you can invert the alpha channel before you write it, so that 0 isfully transparent and 255 (in 8-bit or paletted images) or 65535(in 16-bit images) is fully opaque, with
png_set_invert_alpha(png_ptr);
This must appear before png_write_info() instead of later with theother transformations because in the case of paletted images the tRNSchunk data has to be inverted before the tRNS chunk is written. Ifyour image is not a paletted image, the tRNS data (which in such casesrepresents a single color to be rendered as transparent) won't need tobe changed, and you can safely do this transformation after yourpng_write_info() call.
If you need to write a private chunk that you want to appear beforethe PLTE chunk when PLTE is present, you can write the PNG info intwo steps, and insert code to write your own chunk between them:
png_write_info_before_PLTE(png_ptr, info_ptr); png_set_unknown_chunks(png_ptr, info_ptr, ...); png_write_info(png_ptr, info_ptr);
After you've written the file information, you can set up the libraryto handle any special transformations of the image data. The variousways to transform the data will be described in the order that theyshould occur. This is important, as some of these change the colortype and/or bit depth of the data, and some others only work oncertain color types and bit depths. Even though each transformationchecks to see if it has data that it can do something with, you shouldmake sure to only enable a transformation if it will be valid for thedata. For example, don't swap red and blue on grayscale data.
PNG files store RGB pixels packed into 3 or 6 bytes. This code tellsthe library to strip input data that has 4 or 8 bytes per pixel downto 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2bytes per pixel).
png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
where the 0 is unused, and the location is either PNG_FILLER_BEFORE orPNG_FILLER_AFTER, depending upon whether the filler byte in the pixelis stored XRGB or RGBX.
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small asthey can, resulting in, for example, 8 pixels per byte for 1 bit files.If the data is supplied at 1 pixel per byte, use this code, which willcorrectly pack the pixels into a single byte:
png_set_packing(png_ptr);
PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If yourdata is of another bit depth, you can write an sBIT chunk into thefile so that decoders can recover the original data if desired.
/* Set the true bit depth of the image data */ if (color_type & PNG_COLOR_MASK_COLOR) { sig_bit.red = true_bit_depth; sig_bit.green = true_bit_depth; sig_bit.blue = true_bit_depth; }
else { sig_bit.gray = true_bit_depth; }
if (color_type & PNG_COLOR_MASK_ALPHA) { sig_bit.alpha = true_bit_depth; }
png_set_sBIT(png_ptr, info_ptr, &sig_bit);
If the data is stored in the row buffer in a bit depth other thanone supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),this will scale the values to appear to be the correct bit depth asis required by PNG.
png_set_shift(png_ptr, &sig_bit);
PNG files store 16 bit pixels in network byte order (big-endian,ie. most significant bits first). This code would be used if they aresupplied the other way (little-endian, i.e. least significant bitsfirst, the way PCs store them):
if (bit_depth > 8) png_set_swap(png_ptr);
If you are using packed-pixel images (1, 2, or 4 bits/pixel), and youneed to change the order the pixels are packed into bytes, you can use:
if (bit_depth < 8) png_set_packswap(png_ptr);
PNG files store 3 color pixels in red, green, blue order. This codewould be used if they are supplied as blue, green, red:
png_set_bgr(png_ptr);
PNG files describe monochrome as black being zero and white beingone. This code would be used if the pixels are supplied with this reversed(black being one and white being zero):
png_set_invert_mono(png_ptr);
Finally, you can write your own transformation function if none ofthe existing ones meets your needs. This is done by setting a callbackwith
png_set_write_user_transform_fn(png_ptr, write_transform_fn);
You must supply the function
void write_transform_fn(png_structp png_ptr, png_row_infop row_info, png_bytep data)
See pngtest.c for a working example. Your function will be calledbefore any of the other transformations are processed. If supportedlibpng also supplies an information routine that may be called fromyour callback:
png_get_current_row_number(png_ptr); png_get_current_pass_number(png_ptr);
This returns the current row passed to the transform. With interlacedimages the value returned is the row in the input sub-image image. UsePNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) tofind the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
The discussion of interlace handling above contains more information on how touse these values.
You can also set up a pointer to a user structure for use by yourcallback function.
png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
The user_channels and user_depth parameters of this function are ignoredwhen writing; you can set them to zero as shown.
You can retrieve the pointer via the function png_get_user_transform_ptr().For example:
voidp write_user_transform_ptr = png_get_user_transform_ptr(png_ptr);
It is possible to have libpng flush any pending output, either manually,or automatically after a certain number of lines have been written. Toflush the output stream a single time call:
png_write_flush(png_ptr);
and to have libpng flush the output stream periodically after a certainnumber of scanlines have been written, call:
png_set_flush(png_ptr, nrows);
Note that the distance between rows is from the last time png_write_flush()was called, or the first row of the image if it has never been called.So if you write 50 lines, and then png_set_flush 25, it will flush theoutput on the next scanline, and every 25 lines thereafter, unlesspng_write_flush() is called before 25 more lines have been written.If nrows is too small (less than about 10 lines for a 640 pixel wideRGB image) the image compression may decrease noticeably (although thismay be acceptable for real-time applications). Infrequent flushing willonly degrade the compression performance by a few percent over imagesthat do not use flushing.
.SS Writing the image data
That's it for the transformations. Now you can write the image data.The simplest way to do this is in one function call. If you have thewhole image in memory, you can just call png_write_image() and libpngwill write the image. You will need to pass in an array of pointers toeach row. This function automatically handles interlacing, so you don'tneed to call png_set_interlace_handling() or call this function multipletimes, or any of that other stuff necessary with png_write_rows().
png_write_image(png_ptr, row_pointers);
where row_pointers is:
png_byte *row_pointers[height];
You can point to void or char or whatever you use for pixels.
If you don't want to write the whole image at once, you canuse png_write_rows() instead. If the file is not interlaced,this is simple:
png_write_rows(png_ptr, row_pointers, number_of_rows);
row_pointers is the same as in the png_write_image() call.
If you are just writing one row at a time, you can do this witha single row_pointer instead of an array of row_pointers:
png_bytep row_pointer = row;
png_write_row(png_ptr, row_pointer);
When the file is interlaced, things can get a good deal more complicated.The only currently (as of the PNG Specification version 1.2, dated July1999) defined interlacing scheme for PNG files is the "Adam7" interlacescheme, that breaks down an image into seven smaller images of varyingsize. libpng will build these images for you, or you can do themyourself. If you want to build them yourself, see the PNG specificationfor details of which pixels to write when.
If you don't want libpng to handle the interlacing details, justuse png_set_interlace_handling() and call png_write_rows() thecorrect number of times to write all the sub-images(png_set_interlace_handling() returns the number of sub-images.)
If you want libpng to build the sub-images, call this before you startwriting any rows:
number_of_passes = png_set_interlace_handling(png_ptr);
This will return the number of passes needed. Currently, this is seven,but may change if another interlace type is added.
Then write the complete image number_of_passes times.
png_write_rows(png_ptr, row_pointers, number_of_rows);
Think carefully before you write an interlaced image. Typically code thatreads such images reads all the image data into memory, uncompressed, beforedoing any processing. Only code that can display an image on the fly cantake advantage of the interlacing and even then the image has to be exactlythe correct size for the output device, because scaling an image requiresadjacent pixels and these are not available until all the passes have beenread.
If you do write an interlaced image you will hardly ever need to handlethe interlacing yourself. Call png_set_interlace_handling() and use theapproach described above.
The only time it is conceivable that you will really need to write aninterlaced image pass-by-pass is when you have read one pass by pass andmade some pixel-by-pixel transformation to it, as described in the readcode above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macrosto determine the size of each sub-image in turn and simply write the rowsyou obtained from the read code.
.SS Finishing a sequential write
After you are finished writing the image, you should finish writingthe file. If you are interested in writing comments or time, you shouldpass an appropriately filled png_info pointer. If you are not interested,you can pass NULL.
png_write_end(png_ptr, info_ptr);
When you are done, you can free all memory used by libpng like this:
png_destroy_write_struct(&png_ptr, &info_ptr);
It is also possible to individually free the info_ptr members thatpoint to libpng-allocated storage with the following function:
png_free_data(png_ptr, info_ptr, mask, seq)
mask - identifies data to be freed, a mask containing the bitwise OR of one or more of PNG_FREE_PLTE, PNG_FREE_TRNS, PNG_FREE_HIST, PNG_FREE_ICCP, PNG_FREE_PCAL, PNG_FREE_ROWS, PNG_FREE_SCAL, PNG_FREE_SPLT, PNG_FREE_TEXT, PNG_FREE_UNKN, or simply PNG_FREE_ALL
seq - sequence number of item to be freed (-1 for all items)
This function may be safely called when the relevant storage hasalready been freed, or has not yet been allocated, or was allocatedby the user and not by libpng, and will in those cases do nothing.The "seq" parameter is ignored if only one item of the selected datatype, such as PLTE, is allowed. If "seq" is not -1, and multiple itemsare allowed for the data type identified in the mask, such as text orsPLT, only the n'th item in the structure is freed, where n is "seq".
If you allocated data such as a palette that you passed in to libpngwith png_set_*, you must not free it until just before the call topng_destroy_write_struct().
The default behavior is only to free data that was allocated internallyby libpng. This can be changed, so that libpng will not free the data,or so that it will free data that was allocated by the user with png_malloc()or png_zalloc() and passed in via a png_set_*() function, with
png_data_freer(png_ptr, info_ptr, freer, mask)
freer - one of PNG_DESTROY_WILL_FREE_DATA PNG_SET_WILL_FREE_DATA PNG_USER_WILL_FREE_DATA
mask - which data elements are affected same choices as in png_free_data()
For example, to transfer responsibility for some data from a read structureto a write structure, you could use
png_data_freer(read_ptr, read_info_ptr, PNG_USER_WILL_FREE_DATA, PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
png_data_freer(write_ptr, write_info_ptr, PNG_DESTROY_WILL_FREE_DATA, PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
thereby briefly reassigning responsibility for freeing to the user butimmediately afterwards reassigning it once more to the write_destroyfunction. Having done this, it would then be safe to destroy the readstructure and continue to use the PLTE, tRNS, and hIST data in the writestructure.
This function only affects data that has already been allocated.You can call this function before calling after the png_set_*() functionsto control whether the user or png_destroy_*() is supposed to free the data.When the user assumes responsibility for libpng-allocated data, theapplication must usepng_free() to free it, and when the user transfers responsibility to libpngfor data that the user has allocated, the user must have used png_malloc()or png_zalloc() to allocate it.
If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keywordseparately, do not transfer responsibility for freeing text_ptr to libpng,because when libpng fills a png_text structure it combines these members withthe key member, and png_free_data() will free only text_ptr.key. Similarly,if you transfer responsibility for free'ing text_ptr from libpng to yourapplication, your application must not separately free those members.For a more compact example of writing a PNG image, see the file example.c.
.SH V. Modifying/Customizing libpng:
There are two issues here. The first is changing how libpng doesstandard things like memory allocation, input/output, and error handling.The second deals with more complicated things like adding new chunks,adding new transformations, and generally changing how libpng works.Both of those are compile-time issues; that is, they are generallydetermined at the time the code is written, and there is rarely a needto provide the user with a means of changing them.
Memory allocation, input/output, and error handling
All of the memory allocation, input/output, and error handling in libpnggoes through callbacks that are user-settable. The default routines arein pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To changethese functions, call the appropriate png_set_*_fn() function.
Memory allocation is done through the functions png_malloc(), png_calloc(),and png_free(). These currently just call the standard C functions.png_calloc() calls png_malloc() and then clears the newlyallocated memory to zero. There is limited support for certain systemswith segmented memory architectures and the types of pointers declared bypng.h match this; you will have to use appropriate pointers in yourapplication. Since it isunlikely that the method of handling memory allocation on a platformwill change between applications, these functions must be modified inthe library at compile time. If you prefer to use a different methodof allocating and freeing data, you can use png_create_read_struct_2() orpng_create_write_struct_2() to register your own functions as describedabove. These functions also provide a void pointer that can be retrievedvia
mem_ptr=png_get_mem_ptr(png_ptr);
Your replacement memory functions must have prototypes as follows:
png_voidp malloc_fn(png_structp png_ptr, png_alloc_size_t size);
void free_fn(png_structp png_ptr, png_voidp ptr);
Your malloc_fn() must return NULL in case of failure. The png_malloc()function will normally call png_error() if it receives a NULL from thesystem memory allocator or from your replacement malloc_fn().
Your free_fn() will never be called with a NULL ptr, since libpng'spng_free() checks for NULL before calling free_fn().
Input/Output in libpng is done through png_read() and png_write(),which currently just call fread() and fwrite(). The FILE * is stored inpng_struct and is initialized via png_init_io(). If you wish to changethe method of I/O, the library supplies callbacks that you can setthrough the function png_set_read_fn() and png_set_write_fn() at runtime, instead of calling the png_init_io() function. These functionsalso provide a void pointer that can be retrieved via the functionpng_get_io_ptr(). For example:
png_set_read_fn(png_structp read_ptr, voidp read_io_ptr, png_rw_ptr read_data_fn)
png_set_write_fn(png_structp write_ptr, voidp write_io_ptr, png_rw_ptr write_data_fn, png_flush_ptr output_flush_fn);
voidp read_io_ptr = png_get_io_ptr(read_ptr); voidp write_io_ptr = png_get_io_ptr(write_ptr);
The replacement I/O functions must have prototypes as follows:
void user_read_data(png_structp png_ptr, png_bytep data, png_size_t length);
void user_write_data(png_structp png_ptr, png_bytep data, png_size_t length);
void user_flush_data(png_structp png_ptr);
The user_read_data() function is responsible for detecting andhandling end-of-data errors.
Supplying NULL for the read, write, or flush functions sets them backto using the default C stream functions, which expect the io_ptr topoint to a standard *FILE structure. It is probably a mistaketo use NULL for one of write_data_fn and output_flush_fn but not bothof them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.It is an error to read from a write stream, and vice versa.
Error handling in libpng is done through png_error() and png_warning().Errors handled through png_error() are fatal, meaning that png_error()should never return to its caller. Currently, this is handled viasetjmp() and longjmp() (unless you have compiled libpng withPNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),but you could change this to do things like exit() if you should wish,as long as your function does not return.
On non-fatal errors, png_warning() is calledto print a warning message, and then control returns to the calling code.By default png_error() and png_warning() print a message on stderr viafprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined(because you don't want the messages) or PNG_NO_STDIO defined (becausefprintf() isn't available). If you wish to change the behavior of the errorfunctions, you will need to set up your own message callbacks. Thesefunctions are normally supplied at the time that the png_struct is created.It is also possible to redirect errors and warnings to your own replacementfunctions after png_create_*_struct() has been called by calling:
png_set_error_fn(png_structp png_ptr, png_voidp error_ptr, png_error_ptr error_fn, png_error_ptr warning_fn);
png_voidp error_ptr = png_get_error_ptr(png_ptr);
If NULL is supplied for either error_fn or warning_fn, then the libpngdefault function will be used, calling fprintf() and/or longjmp() if aproblem is encountered. The replacement error functions should haveparameters as follows:
void user_error_fn(png_structp png_ptr, png_const_charp error_msg);
void user_warning_fn(png_structp png_ptr, png_const_charp warning_msg);
The motivation behind using setjmp() and longjmp() is the C++ throw andcatch exception handling methods. This makes the code much easier to write,as there is no need to check every return code of every function call.However, there are some uncertainties about the status of local variablesafter a longjmp, so the user may want to be careful about doing anythingafter setjmp returns non-zero besides returning itself. Consult yourcompiler documentation for more details. For an alternative approach, youmay wish to use the "cexcept" facility (see http://cexcept.sourceforge.net).
.SS Custom chunks
If you need to read or write custom chunks, you may need to get deeperinto the libpng code. The library now has mechanisms for storingand writing chunks of unknown type; you can even declare callbacksfor custom chunks. However, this may not be good enough if thelibrary code itself needs to know about interactions between yourchunk and existing `intrinsic' chunks.
If you need to write a new intrinsic chunk, first read the PNGspecification. Acquire a first level of understanding of how it works.Pay particular attention to the sections that describe chunk names,and look at how other chunks were designed, so you can do thingssimilarly. Second, check out the sections of libpng that read andwrite chunks. Try to find a chunk that is similar to yours and useit as a template. More details can be found in the comments insidethe code. It is best to handle unknown chunks in a generic method,via callback functions, instead of by modifying libpng functions.
If you wish to write your own transformation for the data, look throughthe part of the code that does the transformations, and check out some ofthe simpler ones to get an idea of how they work. Try to find a similartransformation to the one you want to add and copy off of it. More detailscan be found in the comments inside the code itself.
.SS Configuring for 16 bit platforms
You will want to look into zconf.h to tell zlib (and thus libpng) thatit cannot allocate more then 64K at a time. Even if you can, the memorywon't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
.SS Configuring for DOS
For DOS users who only have access to the lower 640K, you willhave to limit zlib's memory usage via a png_set_compression_mem_level()call. See zlib.h or zconf.h in the zlib library for more information.
.SS Configuring for Medium Model
Libpng's support for medium model has been tested on most of the popularcompilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD getsdefined, and FAR gets defined to far in pngconf.h, and you should beall set. Everything in the library (except for zlib's structure) isexpecting far data. You must use the typedefs with the p or pp onthe end for pointers (or at least look at them and be careful). Makenote that the rows of data are defined as png_bytepp, which is anunsigned char far * far *.
.SS Configuring for gui/windowing platforms:
You will need to write new error and warning functions that use the GUIinterface, as described previously, and set them to be the error andwarning functions at the time that png_create_*_struct() is called,in order to have them available during the structure initialization.They can be changed later via png_set_error_fn(). On some compilers,you may also have to change the memory allocators (png_malloc, etc.).
.SS Configuring for compiler xxx:
All includes for libpng are in pngconf.h. If you need to add, changeor delete an include, this is the place to do it.The includes that are not needed outside libpng are placed in pngpriv.h,which is only used by the routines inside libpng itself.The files in libpng proper only include pngpriv.h and png.h, whichin turn includes pngconf.h.
.SS Configuring zlib:
There are special functions to configure the compression. Perhaps themost useful one changes the compression level, which currently usesinput compression values in the range 0 - 9. The library normallyuses the default compression level (Z_DEFAULT_COMPRESSION = 6). Testshave shown that for a large majority of images, compression values inthe range 3-6 compress nearly as well as higher levels, and do so muchfaster. For online applications it may be desirable to have maximum speed(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can alsospecify no compression (Z_NO_COMPRESSION = 0), but this would createfiles larger than just storing the raw bitmap. You can specify thecompression level by calling:
#include zlib.h png_set_compression_level(png_ptr, level);
Another useful one is to reduce the memory level used by the library.The memory level defaults to 8, but it can be lowered if you areshort on memory (running DOS, for example, where you only have 640K).Note that the memory level does have an effect on compression; amongother things, lower levels will result in sections of incompressibledata being emitted in smaller stored blocks, with a correspondinglylarger relative overhead of up to 15% in the worst case.
#include zlib.h png_set_compression_mem_level(png_ptr, level);
The other functions are for configuring zlib. They are not recommendedfor normal use and may result in writing an invalid PNG file. Seezlib.h for more information on what these mean.
#include zlib.h png_set_compression_strategy(png_ptr, strategy);
png_set_compression_window_bits(png_ptr, window_bits);
png_set_compression_method(png_ptr, method); png_set_compression_buffer_size(png_ptr, size);
.SS Controlling row filtering
If you want to control whether libpng uses filtering or not, whichfilters are used, and how it goes about picking row filters, youcan call one of these functions. The selection and configurationof row filters can have a significant impact on the size andencoding speed and a somewhat lesser impact on the decoding speedof an image. Filtering is enabled by default for RGB and grayscaleimages (with and without alpha), but not for paletted images norfor any images with bit depths less than 8 bits/pixel.
The 'method' parameter sets the main filtering method, which iscurrently only '0' in the PNG 1.2 specification. The 'filters'parameter sets which filter(s), if any, should be used for eachscanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERSto turn filtering on and off, respectively.
Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwiseORed together with '|' to specify one or more filters to use.These filters are described in more detail in the PNG specification.If you intend to change the filter type during the course of writingthe image, you should start with flags set for all of the filtersyou intend to use so that libpng can initialize its internalstructures appropriately for all of the filter types. (Note that thismeans the first row must always be adaptively filtered, because libpngcurrently does not allocate the filter buffers until png_write_row()is called for the first time.)
filters = PNG_FILTER_NONE | PNG_FILTER_SUB PNG_FILTER_UP | PNG_FILTER_AVG | PNG_FILTER_PAETH | PNG_ALL_FILTERS;
png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, filters); The second parameter can also be PNG_INTRAPIXEL_DIFFERENCING if you are writing a PNG to be embedded in a MNG datastream. This parameter must be the same as the value of filter_method used in png_set_IHDR().
It is also possible to influence how libpng chooses from among theavailable filters. This is done in one or both of two ways - bytelling it how important it is to keep the same filter for successiverows, and by telling it the relative computational costs of the filters.
double weights[3] = {1.5, 1.3, 1.1}, costs[PNG_FILTER_VALUE_LAST] = {1.0, 1.3, 1.3, 1.5, 1.7};
png_set_filter_heuristics(png_ptr, PNG_FILTER_HEURISTIC_WEIGHTED, 3, weights, costs);
The weights are multiplying factors that indicate to libpng that therow filter should be the same for successive rows unless another row filteris that many times better than the previous filter. In the above example,if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a"sum of absolute differences" 1.5 x 1.3 times higher than other filtersand still be chosen, while the NONE filter could have a sum 1.1 timeshigher than other filters and still be chosen. Unspecified weights aretaken to be 1.0, and the specified weights should probably be declininglike those above in order to emphasize recent filters over older filters.
The filter costs specify for each filter type a relative decoding costto be considered when selecting row filters. This means that filterswith higher costs are less likely to be chosen over filters with lowercosts, unless their "sum of absolute differences" is that much smaller.The costs do not necessarily reflect the exact computational speeds ofthe various filters, since this would unduly influence the final imagesize.
Note that the numbers above were invented purely for this example andare given only to help explain the function usage. Little testing hasbeen done to find optimum values for either the costs or the weights.
.SS Removing unwanted object code
There are a bunch of #define's in pngconf.h that control what parts oflibpng are compiled. All the defines end in _SUPPORTED. If you arenever going to use a capability, you can change the #define to #undefbefore recompiling libpng and save yourself code and data space, oryou can turn off individual capabilities with defines that begin withPNG_NO_.
In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
You can also turn all of the transforms and ancillary chunk capabilitiesoff en masse with compiler directives that definePNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,or all four,along with directives to turn on any of the capabilities that you dowant. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extratransformations but still leave the library fully capable of readingand writing PNG files with all known public chunks. Use of thePNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a librarythat is incapable of reading or writing ancillary chunks. If you arenot using the progressive reading capability, you can turn that offwith PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACINGcapability, which you'll still have).
All the reading and writing specific code are in separate files, so thelinker should only grab the files it needs. However, if you want tomake sure, or if you are building a stand alone library, all thereading files start with pngr and all the writing files start withpngw. The files that don't match either (like png.c, pngtrans.c, etc.)are used for both reading and writing, and always need to be included.The progressive reader is in pngpread.c
If you are creating or distributing a dynamically linked library (a .soor DLL file), you should not remove or disable any parts of the library,as this will cause applications linked with different versions of thelibrary to fail if they call functions not available in your library.The size of the library itself should not be an issue, because onlythose sections that are actually used will be loaded into memory.
.SS Requesting debug printout
The macro definition PNG_DEBUG can be used to request debuggingprintout. Set it to an integer value in the range 0 to 3. Highernumbers result in increasing amounts of debugging information. Theinformation is printed to the "stderr" file, unless another filename is specified in the PNG_DEBUG_FILE macro definition.
When PNG_DEBUG > 0, the following functions (macros) become available:
png_debug(level, message) png_debug1(level, message, p1) png_debug2(level, message, p1, p2)
in which "level" is compared to PNG_DEBUG to decide whether to printthe message, "message" is the formatted string to be printed,and p1 and p2 are parameters that are to be embedded in the stringaccording to printf-style formatting directives. For example,
png_debug1(2, "foo=%d\n", foo);
is expanded to
if (PNG_DEBUG > 2) fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
When PNG_DEBUG is defined but is zero, the macros aren't defined, but youcan still use PNG_DEBUG to control your own debugging:
#ifdef PNG_DEBUG fprintf(stderr, ... #endif
When PNG_DEBUG = 1, the macros are defined, but only png_debug statementshaving level = 0 will be printed. There aren't any such statements inthis version of libpng, but if you insert some they will be printed.
.SH VI. MNG support
The MNG specification (available at http://www.libpng.org/pub/mng) allowscertain extensions to PNG for PNG images that are embedded in MNG datastreams.Libpng can support some of these extensions. To enable them, use thepng_permit_mng_features() function:
feature_set = png_permit_mng_features(png_ptr, mask)
mask is a png_uint_32 containing the bitwise OR of the features you want to enable. These include PNG_FLAG_MNG_EMPTY_PLTE PNG_FLAG_MNG_FILTER_64 PNG_ALL_MNG_FEATURES
feature_set is a png_uint_32 that is the bitwise AND of your mask with the set of MNG features that is supported by the version of libpng that you are using.
It is an error to use this function when reading or writing a standalonePNG file with the PNG 8-byte signature. The PNG datastream must be wrappedin a MNG datastream. As a minimum, it must have the MNG 8-byte signatureand the MHDR and MEND chunks. Libpng does not provide support for theseor any other MNG chunks; your application must provide its own support forthem. You may wish to consider using libmng (available athttp://www.libmng.com) instead.
.SH VII. Changes to Libpng from version 0.88
It should be noted that versions of libpng later than 0.96 are notdistributed by the original libpng author, Guy Schalnat, nor byAndreas Dilger, who had taken over from Guy during 1996 and 1997, anddistributed versions 0.89 through 0.96, but rather by another memberof the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas arestill alive and well, but they have moved on to other things.
The old libpng functions png_read_init(), png_write_init(),png_info_init(), png_read_destroy(), and png_write_destroy() have beenmoved to PNG_INTERNAL in version 0.95 to discourage their use. Thesefunctions will be removed from libpng version 1.4.0.
The preferred method of creating and initializing the libpng structures isvia the png_create_read_struct(), png_create_write_struct(), andpng_create_info_struct() because they isolate the size of the structuresfrom the application, allow version error checking, and also allow theuse of custom error handling routines during the initialization, whichthe old functions do not. The functions png_read_destroy() andpng_write_destroy() do not actually free the memory that libpngallocated for these structs, but just reset the data structures, so theycan be used instead of png_destroy_read_struct() andpng_destroy_write_struct() if you feel there is too much system overheadallocating and freeing the png_struct for each image read.
Setting the error callbacks via png_set_message_fn() beforepng_read_init() as was suggested in libpng-0.88 is no longer supportedbecause this caused applications that do not use custom error functionsto fail if the png_ptr was not initialized to zero. It is still possibleto set the error callbacks AFTER png_read_init(), or to change them withpng_set_error_fn(), which is essentially the same function, but with a newname to force compilation errors with applications that try to use the oldmethod.
Starting with version 1.0.7, you can find out which version of the libraryyou are using at run-time:
png_uint_32 libpng_vn = png_access_version_number();
The number libpng_vn is constructed from the major version, minorversion with leading zero, and release number with leading zero,(e.g., libpng_vn for version 1.0.7 is 10007).
You can also check which version of png.h you used when compiling yourapplication:
png_uint_32 application_vn = PNG_LIBPNG_VER;
.SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
Support for user memory management was enabled by default. Toaccomplish this, the functions png_create_read_struct_2(),png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),png_malloc_default(), and png_free_default() were added.
Support for the iTXt chunk has been enabled by default as ofversion 1.2.41.
Support for certain MNG features was enabled.
Support for numbered error messages was added. However, we never gotaround to actually numbering the error messages. The functionpng_set_strip_error_numbers() was added (Note: the prototype for thisfunction was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODEbuilds of libpng-1.2.15. It was restored in libpng-1.2.36).
The png_malloc_warn() function was added at libpng-1.2.3. This issuesa png_warning and returns NULL instead of aborting when it fails toacquire the requested memory allocation.
Support for setting user limits on image width and height was enabledby default. The functions png_set_user_limits(), png_get_user_width_max(),and png_get_user_height_max() were added at libpng-1.2.6.
The png_set_add_alpha() function was added at libpng-1.2.7.
The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.Unlike png_set_gray_1_2_4_to_8(), the new function does not expand thetRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function isdeprecated.
A number of macro definitions in support of runtime selection ofassembler code features (especially Intel MMX code support) wereadded at libpng-1.2.0:
PNG_ASM_FLAG_MMX_SUPPORT_COMPILED PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU PNG_ASM_FLAG_MMX_READ_COMBINE_ROW PNG_ASM_FLAG_MMX_READ_INTERLACE PNG_ASM_FLAG_MMX_READ_FILTER_SUB PNG_ASM_FLAG_MMX_READ_FILTER_UP PNG_ASM_FLAG_MMX_READ_FILTER_AVG PNG_ASM_FLAG_MMX_READ_FILTER_PAETH PNG_ASM_FLAGS_INITIALIZED PNG_MMX_READ_FLAGS PNG_MMX_FLAGS PNG_MMX_WRITE_FLAGS PNG_MMX_FLAGS
We added the following functions in support of runtimeselection of assembler code features:
png_get_mmx_flagmask() png_set_mmx_thresholds() png_get_asm_flags() png_get_mmx_bitdepth_threshold() png_get_mmx_rowbytes_threshold() png_set_asm_flags()
We replaced all of these functions with simple stubs in libpng-1.2.20,when the Intel assembler code was removed due to a licensing issue.
These macros are deprecated:
PNG_READ_TRANSFORMS_NOT_SUPPORTED PNG_PROGRESSIVE_READ_NOT_SUPPORTED PNG_NO_SEQUENTIAL_READ_SUPPORTED PNG_WRITE_TRANSFORMS_NOT_SUPPORTED PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
They have been replaced, respectively, by:
PNG_NO_READ_TRANSFORMS PNG_NO_PROGRESSIVE_READ PNG_NO_SEQUENTIAL_READ PNG_NO_WRITE_TRANSFORMS PNG_NO_READ_ANCILLARY_CHUNKS PNG_NO_WRITE_ANCILLARY_CHUNKS
PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has beendeprecated since libpng-1.0.16 and libpng-1.2.6.
The function png_check_sig(sig, num)was replaced with !png_sig_cmp(sig, 0, num)It has been deprecated since libpng-0.90.
The function png_set_gray_1_2_4_to_8()which also expands tRNS to alpha was replaced with png_set_expand_gray_1_2_4_to_8()which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
.SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
Private libpng prototypes and macro definitions were moved frompng.h and pngconf.h into a new pngpriv.h header file.
Functions png_set_benign_errors(), png_benign_error(), andpng_chunk_benign_error() were added.
Support for setting the maximum amount of memory that the applicationwill allocate for reading chunks was added, as a security measure.The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()were added to the library.
We implemented support for I/O states by adding png_ptr member io_stateand functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-levelinput transforms.
Checking for and reporting of errors in the IHDR chunk is more thorough.
Support for global arrays was removed, to improve thread safety.
Some obsolete/deprecated macros and functions have been removed.
Typecasted NULL definitions such as #define png_voidp_NULL (png_voidp)NULLwere eliminated. If you used these in your application, just useNULL instead.
The png_struct and info_struct members "trans" and "trans_values" werechanged to "trans_alpha" and "trans_color", respectively.
The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefileswere removed.
The PNG_1_0_X and PNG_1_2_X macros were eliminated.
The PNG_LEGACY_SUPPORTED macro was eliminated.
Many WIN32_WCE #ifdefs were removed.
The functions png_read_init(info_ptr), png_write_init(info_ptr),png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()have been removed. They have been deprecated since libpng-0.95.
The png_permit_empty_plte() was removed. It has been deprecatedsince libpng-1.0.9. Use png_permit_mng_features() instead.
We removed the obsolete stub functions png_get_mmx_flagmask(),png_set_mmx_thresholds(), png_get_asm_flags(),png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),png_set_asm_flags(), and png_mmx_supported()
We removed the obsolete png_check_sig(), png_memcpy_check(), andpng_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),and memset(), respectively.
The function png_set_gray_1_2_4_to_8() was removed. It has beendeprecated since libpng-1.0.18 and 1.2.9, when it was replaced withpng_set_expand_gray_1_2_4_to_8() because the former function alsoexpanded any tRNS chunk to an alpha channel.
Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32were added and are used by default instead of the correspondingfunctions. Unfortunately,from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not thefunction) incorrectly returned a value of type png_uint_32.
We changed the prototype for png_malloc() from png_malloc(png_structp png_ptr, png_uint_32 size)to png_malloc(png_structp png_ptr, png_alloc_size_t size)
This also applies to the prototype for the user replacement malloc_fn().
The png_calloc() function was added and is used in place ofof "png_malloc(); memset();" except in the case in png_read_png()where the array consists of pointers; in this case a "for" loop is usedafter the png_malloc() to set the pointers to NULL, to give robust.behavior in case the application runs out of memory part-way throughthe process.
We changed the prototypes of png_get_compression_buffer_size() andpng_set_compression_buffer_size() to work with png_size_t instead ofpng_uint_32.
Support for numbered error messages was removed by default, since wenever got around to actually numbering the error messages. The functionpng_set_strip_error_numbers() was removed from the library by default.
The png_zalloc() and png_zfree() functions are no longer exported.The png_zalloc() function no longer zeroes out the memory that itallocates.
Support for dithering was disabled by default in libpng-1.4.0, becausebeen well tested and doesn't actually "dither". The code was notremoved, however, and could be enabled by building libpng withPNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this supportwas reenabled, but the function was renamed png_set_quantize() toreflect more accurately what it actually does. At the same time,the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed toPNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTEDwas renamed to PNG_READ_QUANTIZE_SUPPORTED.
We removed the trailing '.' from the warning and error messages.
.SH X. Changes to Libpng from version 1.4.x to 1.5.x
From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not thefunction) incorrectly returned a value of type png_uint_32.
A. Changes that affect users of libpng
There are no substantial API changes between the non-deprecated parts ofthe 1.4.5 API and the 1.5.0 API, however the ability to directly accessthe main libpng control structures, png_struct and png_info, deprecatedin earlier versions of libpng, has been completely removed fromlibpng 1.5.
We no longer include zlib.h in png.h. Applications that need accessto information in zlib.h will need to add the '#include "zlib.h"'directive. It does not matter whether it is placed prior to or afterthe '"#include png.h"' directive.
We moved the png_strcpy(), png_strncpy(), png_strlen(), png_memcpy(),png_memcmp(), png_sprintf, and png_memcpy() macros into a privateheader file (pngpriv.h) that is not accessible to applications.
In png_get_iCCP, the type of "profile" was changed from png_charppto png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
There are changes of form in png.h, including new and changed macros todeclareparts of the API. Some API functions with arguments that are pointers todata not modified within the function have been corrected to declarethese arguments with PNG_CONST.
Much of the internal use of C macros to control the library build has alsochanged and some of this is visible in the exported header files, inparticular the use of macros to control data and API elements visibleduring application compilation may require significant revision toapplication code. (It is extremely rare for an application to do this.)
Any program that compiled against libpng 1.4 and did not use deprecatedfeatures or access internal library structures should compile and workagainst libpng 1.5, except for the change in the prototype forpng_get_iCCP() and png_set_iCCP() API functions mentioned above.
libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing ofinterlaced images. The macros return the number of rows and columns ineach pass and information that can be used to de-interlace and (ifabsolutely necessary) interlace an image.
libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API callsthe application-provided png_longjmp_ptr on the internal, but applicationinitialized, jmpbuf. It is provided as a convenience to avoid the needto use the png_jmpbuf macro, which had the unnecessary side effect ofresetting the internal png_longjmp_ptr value.
libpng 1.5.0 includes a complete fixed point API. By default this ispresent along with the corresponding floating point API. In general thefixed point API is faster and smaller than the floating point one becausethe PNG file format used fixed point, not floating point. This applieseven if the library uses floating point in internal calculations. A newmacro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the libraryuses floating point arithmetic (the default) or fixed point arithmeticinternally for performance critical calculations such as gamma correction.In some cases, the gamma calculations may produce slightly differentresults. This has changed the results in png_rgb_to_gray and in alphacomposition (png_set_background for example). This applies even if theoriginal image was already linear (gamma == 1.0) and, therefore, it isnot necessary to linearize the image. This is because libpng has *not*been changed to optimize that case correctly, yet.
Fixed point support for the sCAL chunk comes with an important caveat;the sCAL specification uses a decimal encoding of floating point valuesand the accuracy of PNG fixed point values is insufficient forrepresentation of these values. Consequently a "string" API(png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of readingarbitrary sCAL chunks in the absence of either the floating point API orinternal floating point calculations.
Applications no longer need to include the optional distribution headerfile pngusr.h or define the corresponding macros during applicationbuild in order to see the correct variant of the libpng API. From 1.5.0application code can check for the corresponding _SUPPORTED macro:
#ifdef PNG_INCH_CONVERSIONS_SUPPORTED /* code that uses the inch conversion APIs. */#endif
This macro will only be defined if the inch conversion functions have beencompiled into libpng. The full set of macros, and whether or not supporthas been compiled in, are available in the header file pnglibconf.h.This header file is specific to the libpng build. Notice that prior to1.5.0 the _SUPPORTED macros would always have the default definition unlessreset by pngusr.h or by explicit settings on the compiler command line.These settings may produce compiler warnings or errors in 1.5.0 becauseof macro redefinition.
From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not thefunction) incorrectly returned a value of type png_uint_32. libpng 1.5.0is consistent with the implementation in 1.4.5 and 1.2.x (where the macrodid not exist.)
Applications can now choose whether to use these macros or to call thecorresponding function by defining PNG_USE_READ_MACROS orPNG_NO_USE_READ_MACROS before including png.h. Notice that this isonly supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0 will lead to a link failure.
B. Changes to the build and configuration of libpng
Details of internal changes to the library code can be found in the CHANGESfile. These will be of no concern to the vast majority of library users orbuilders, however the few who configure libpng to a non-default featureset may need to change how this is done.
There should be no need for library builders to alter build scripts ifthese use the distributed build support - configure or the makefiles -however users of the makefiles may care to update their build scriptsto build pnglibconf.h where the corresponding makefile does not do so.
Building libpng with a non-default configuration has changed completely.The old method using pngusr.h should still work correctly even though theway pngusr.h is used in the build has been changed, however librarybuilders will probably want to examine the changes to take advantage ofnew capabilities and to simplify their build system.
B.1 Specific changes to library configuration capabilities
The library now supports a complete fixed point implementation and canthus be used on systems which have no floating point support or verylimited or slow support. Previously gamma correction, an essential partof complete PNG support, required reasonably fast floating point.
As part of this the choice of internal implementation has been madeindependent of the choice of fixed versus floating point APIs and all themissing fixed point APIs have been implemented.
The exact mechanism used to control attributes of API functions haschanged. A single set of operating system independent macro definitionsis used and operating system specific directives are defined inpnglibconf.h
As part of this the mechanism used to choose procedure call standards onthose systems that allow a choice has been changed. At present this onlyaffects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systemsrunning on Intel processors. As before PNGAPI is defined where requiredto control the exported API functions; however, two new macros, PNGCBAPIand PNGCAPI, are used instead for callback functions (PNGCBAPI) and(PNGCAPI) for functions that must match a C library prototype (currentlyonly png_longjmp_ptr, which must match the C longjmp function.) The newapproach is documented in pngconf.h
Despite these changes libpng 1.5.0 only supports the native C functioncalling standard on those platforms tested so far (__cdecl on MicrosoftWindows). This is because the support requirements for alternativecalling conventions seem to no longer exist. Developers who find itnecessary to set PNG_API_RULE to 1 should advise the mailing list(png-mng-implement) of this and library builders who use Openwatcom andtherefore set PNG_API_RULE to 2 should also contact the mailing list.
A new test program, pngvalid, is provided in addition to pngtest.pngvalid validates the arithmetic accuracy of the gamma correctioncalculations and includes a number of validations of the file format.A subset of the full range of tests is run when "make check" is done(in the 'configure' build.) pngvalid also allows total allocated memoryusage to be evaluated and performs additional memory overwrite validation.
Many changes to individual feature macros have been made. The followingare the changes most likely to be noticed by library builders whoconfigure libpng:
1) All feature macros now have consistent naming:
#define PNG_NO_feature turns the feature off#define PNG_feature_SUPPORTED turns the feature on
pnglibconf.h contains one line for each feature macro which is either:
#define PNG_feature_SUPPORTED
if the feature is supported or:
/*#undef PNG_feature_SUPPORTED*/
if it is not. Library code consistently checks for the 'SUPPORTED' macro.It does not, and should not, check for the 'NO' macro which will notnormally be defined even if the feature is not supported.
Compatibility with the old names is provided as follows:
PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
And the following definitions disable the corresponding feature:
PNG_SETJMP_NOT_SUPPORTED disables SETJMPPNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMSPNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIVPNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMSPNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKSPNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
Library builders should remove use of the above, inconsistent, names.
2) Warning and error message formatting was previously conditional onthe STDIO feature. The library has been changed to use theCONSOLE_IO feature instead. This means that if CONSOLE_IO is disabledthe library no longer uses the printf(3) functions, even though thedefault read/write implementations use (FILE) style stdio.h functions.
3) Three feature macros now control the fixed/floating point decisions:
PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, inpractice these are normally required internally anyway (because the PNGfile format is fixed point), therefore in most cases PNG_NO_FIXED_POINTmerely stops the function from being exported.
PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floatingpoint implementation or the fixed point one. Typically the fixed pointimplementation is larger and slower than the floating point implementationon a system that supports floating point, however it may be faster on asystem which lacks floating point hardware and therefore uses a softwareemulation.
4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows thefunctions to read and write ints to be disabled independently ofPNG_USE_READ_MACROS, which allows libpng to be built with the functionseven though the default is to use the macros - this allows applicationsto choose at app buildtime whether or not to use macros (previouslyimpossible because the functions weren't in the default build.)
B.2 Changes to the configuration mechanism
Prior to libpng-1.5.0 library builders who needed to configure libpnghad either to modify the exported pngconf.h header file to add systemspecific configuration or had to write feature selection macros intopngusr.h and cause this to be included into pngconf.h by definingPNG_USER_CONFIG. The latter mechanism had the disadvantage that anapplication built without PNG_USER_CONFIG defined would see theunmodified, default, libpng API and thus would probably fail to link.
These mechanisms still work in the configure build and in any makefilebuild that builds pnglibconf.h although the feature selection macroshave changed somewhat as described above. In 1.5.0, however, pngusr.h isprocessed only once, when the exported header file pnglibconf.h is built.pngconf.h no longer includes pngusr.h, therefore it is ignored after thebuild of pnglibconf.h and it is never included in an application build.
The rarely used alternative of adding a list of feature macros to theCFLAGS setting in the build also still works, however the macros will becopied to pnglibconf.h and this may produce macro redefinition warningswhen the individual C files are compiled.
All configuration now only works if pnglibconf.h is built fromscripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan(the original author of awk) maintains C source code of that awk and thisand all known later implementations (often called by subtly differentnames - nawk and gawk for example) are adequate to build pnglibconf.h.The Sun Microsystems (now Oracle) program 'awk' is an earlier versionand does not work, this may also apply to other systems that have afunctioning awk called 'nawk'.
Configuration options are now documented in scripts/pnglibconf.dfa. Thisfile also includes dependency information that ensures a configuration isconsistent; that is, if a feature is switched off dependent features arealso removed. As a recommended alternative to using feature macros inpngusr.h a system builder may also define equivalent options in pngusr.dfa(or, indeed, any file) and add that to the configuration by settingDFA_XTRA to the file name. The makefiles in contrib/pngminim illustratehow to do this, and a case where pngusr.h is still required.
.SH XI. Detecting libpng
The png_get_io_ptr() function has been present since libpng-0.88, has neverchanged, and is unaffected by conditional compilation macros. It is thebest choice for use in configure scripts for detecting the presence of anylibpng version since 0.88. In an autoconf "configure.in" you could use
AC_CHECK_LIB(png, png_get_io_ptr, ...
.SH XII. Source code repository
Since about February 2009, version 1.2.34, libpng has been under "git" sourcecontrol. The git repository was built from old libpng-x.y.z.tar.gz filesgoing back to version 0.70. You can access the git repository (read only)at
git://libpng.git.sourceforge.net/gitroot/libpng
or you can browse it via "gitweb" at
http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
Patches can be sent to glennrp at users.sourceforge.net or topng-mng-implement at lists.sourceforge.net or you can upload them tothe libpng bug tracker at
http://libpng.sourceforge.net
We also accept patches built from the tar or zip distributions, andsimple verbal discriptions of bug fixes, reported either to theSourceForge bug tracker or to the png-mng-implement at lists.sf.netmailing list.
.SH XIII. Coding style
Our coding style is similar to the "Allman" style, with curlybraces on separate lines:
if (condition) { action; }
else if (another condition) { another action; }
The braces can be omitted from simple one-line actions:
if (condition) return (0);
We use 3-space indentation, except for continued statements whichare usually indented the same as the first line of the statementplus four more spaces.
For macro definitions we use 2-space indentation, always leaving the "#"in the first column.
#ifndef PNG_NO_FEATURE # ifndef PNG_FEATURE_SUPPORTED # define PNG_FEATURE_SUPPORTED # endif #endif
Comments appear with the leading "/*" at the same indentation asthe statement that follows the comment:
/* Single-line comment */ statement;
/* This is a multiple-line * comment. */ statement;
Very short comments can be placed after the end of the statementto which they pertain:
statement; /* comment */
We don't use C++ style ("//") comments. We have, however,used them in the past in some now-abandoned MMX assemblercode.
Functions and their curly braces are not indented, andexported functions are marked with PNGAPI:
/* This is a public function that is visible to * application programmers. It does thus-and-so. */ void PNGAPI png_exported_function(png_ptr, png_info, foo) { body; }
The prototypes for all exported functions appear in png.h,above the comment that says
/* Maintainer: Put new public prototypes here ... */
We mark all non-exported functions with "/* PRIVATE */"":
void /* PRIVATE */ png_non_exported_function(png_ptr, png_info, foo) { body; }
The prototypes for non-exported functions (except for those inpngtest) appear inpngpriv.habove the comment that says
/* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
To avoid polluting the global namespace, the names of all exportedfunctions and variables begin with "png_", and all publicly visible Cpreprocessor macros begin with "PNG_". We request that applications thatuse libpng *not* begin any of their own symbols with either of these strings.
We put a space after each comma and after each semicolonin "for" statements, and we put spaces before and after eachC binary operator and after "for" or "while", and before"?". We don't put a space between a typecast and the expressionbeing cast, nor do we put one between a function name and theleft parenthesis that follows it:
for (i = 2; i > 0; --i) y[i] = a(x) + (int)b;
We prefer #ifdef and #ifndef to #if defined() and if !defined()when there is only one macro being tested.
We do not use the TAB character for indentation in the C sources.
Lines do not exceed 80 characters.
Other rules can be inferred by inspecting the libpng source.
.SH XIV. Y2K Compliance in libpng
March 31, 2011
Since the PNG Development group is an ad-hoc body, we can't makean official declaration.
This is your unofficial assurance that libpng from version 0.71 andupward through 1.5.2 are Y2K compliant. It is my belief that earlierversions were also Y2K compliant.
Libpng only has three year fields. One is a 2-byte unsigned integer thatwill hold years up to 65535. The other two hold the date in textformat, and will hold years up to 9999.
The integer is "png_uint_16 year" in png_time_struct.
The strings are "png_charp time_buffer" in png_struct and "near_time_buffer", which is a local character string in png.c.
There are seven time-related functions:
png_convert_to_rfc_1123() in png.c (formerly png_convert_to_rfc_1152() in error) png_convert_from_struct_tm() in pngwrite.c, called in pngwrite.c png_convert_from_time_t() in pngwrite.c png_get_tIME() in pngget.c png_handle_tIME() in pngrutil.c, called in pngread.c png_set_tIME() in pngset.c png_write_tIME() in pngwutil.c, called in pngwrite.c
All appear to handle dates properly in a Y2K environment. Thepng_convert_from_time_t() function calls gmtime() to convert from systemclock time, which returns (year - 1900), which we properly convert tothe full 4-digit year. There is a possibility that applications usinglibpng are not passing 4-digit years into the png_convert_to_rfc_1123()function, or that they are incorrectly passing only a 2-digit yearinstead of "year - 1900" into the png_convert_from_struct_tm() function,but this is not under our control. The libpng documentation has alwaysstated that it works with 4-digit years, and the APIs have beendocumented as such.
The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsignedinteger to hold the year, and can hold years as large as 65535.
zlib, upon which libpng depends, is also Y2K compliant. It containsno date-related code.
Glenn Randers-Pehrson libpng maintainer PNG Development Group
.SH NOTE
Note about libpng version numbers:
Due to various miscommunications, unforeseen code incompatibilitiesand occasional factors outside the authors' control, version numberingon the library has not always been consistent and straightforward.The following table summarizes matters since version 0.89c, which wasthe first widely used release:
source png.h png.h shared-lib version string int version ------- ------ ----- ---------- 0.89c ("beta 3") 0.89 89 1.0.89 0.90 ("beta 4") 0.90 90 0.90 0.95 ("beta 5") 0.95 95 0.95 0.96 ("beta 6") 0.96 96 0.96 0.97b ("beta 7") 1.00.97 97 1.0.1 0.97c 0.97 97 2.0.97 0.98 0.98 98 2.0.98 0.99 0.99 98 2.0.99 0.99a-m 0.99 99 2.0.99 1.00 1.00 100 2.1.0 1.0.0 1.0.0 100 2.1.0 1.0.0 (from here on, the 100 2.1.0 1.0.1 png.h string is 10001 2.1.0 1.0.1a-e identical to the 10002 from here on, the 1.0.2 source version) 10002 shared library is 2.V 1.0.2a-b 10003 where V is the source 1.0.1 10001 code version except as 1.0.1a-e 10002 2.1.0.1a-e noted. 1.0.2 10002 2.1.0.2 1.0.2a-b 10003 2.1.0.2a-b 1.0.3 10003 2.1.0.3 1.0.3a-d 10004 2.1.0.3a-d 1.0.4 10004 2.1.0.4 1.0.4a-f 10005 2.1.0.4a-f 1.0.5 (+ 2 patches) 10005 2.1.0.5 1.0.5a-d 10006 2.1.0.5a-d 1.0.5e-r 10100 2.1.0.5e-r 1.0.5s-v 10006 2.1.0.5s-v 1.0.6 (+ 3 patches) 10006 2.1.0.6 1.0.6d-g 10007 2.1.0.6d-g 1.0.6h 10007 10.6h 1.0.6i 10007 10.6i 1.0.6j 10007 2.1.0.6j 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14 1.0.7beta15-18 1 10007 2.1.0.7beta15-18 1.0.7rc1-2 1 10007 2.1.0.7rc1-2 1.0.7 1 10007 2.1.0.7 1.0.8beta1-4 1 10008 2.1.0.8beta1-4 1.0.8rc1 1 10008 2.1.0.8rc1 1.0.8 1 10008 2.1.0.8 1.0.9beta1-6 1 10009 2.1.0.9beta1-6 1.0.9rc1 1 10009 2.1.0.9rc1 1.0.9beta7-10 1 10009 2.1.0.9beta7-10 1.0.9rc2 1 10009 2.1.0.9rc2 1.0.9 1 10009 2.1.0.9 1.0.10beta1 1 10010 2.1.0.10beta1 1.0.10rc1 1 10010 2.1.0.10rc1 1.0.10 1 10010 2.1.0.10 1.0.11beta1-3 1 10011 2.1.0.11beta1-3 1.0.11rc1 1 10011 2.1.0.11rc1 1.0.11 1 10011 2.1.0.11 1.0.12beta1-2 2 10012 2.1.0.12beta1-2 1.0.12rc1 2 10012 2.1.0.12rc1 1.0.12 2 10012 2.1.0.12 1.1.0a-f - 10100 2.1.1.0a-f abandoned 1.2.0beta1-2 2 10200 2.1.2.0beta1-2 1.2.0beta3-5 3 10200 3.1.2.0beta3-5 1.2.0rc1 3 10200 3.1.2.0rc1 1.2.0 3 10200 3.1.2.0 1.2.1beta-4 3 10201 3.1.2.1beta1-4 1.2.1rc1-2 3 10201 3.1.2.1rc1-2 1.2.1 3 10201 3.1.2.1 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6 1.0.13beta1 10 10013 10.so.0.1.0.13beta1 1.0.13rc1 10 10013 10.so.0.1.0.13rc1 1.2.2rc1 12 10202 12.so.0.1.2.2rc1 1.0.13 10 10013 10.so.0.1.0.13 1.2.2 12 10202 12.so.0.1.2.2 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6 1.2.3 12 10203 12.so.0.1.2.3 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3 1.2.4rc1 13 10204 12.so.0.1.2.4rc1 1.0.14 10 10014 10.so.0.1.0.14 1.2.4 13 10204 12.so.0.1.2.4 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2 1.0.15rc1 10 10015 10.so.0.1.0.15rc1 1.0.15 10 10015 10.so.0.1.0.15 1.2.5 13 10205 12.so.0.1.2.5 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5 1.0.16 10 10016 10.so.0.1.0.16 1.2.6 13 10206 12.so.0.1.2.6 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2 1.0.17rc1 10 10017 12.so.0.1.0.17rc1 1.2.7rc1 13 10207 12.so.0.1.2.7rc1 1.0.17 10 10017 12.so.0.1.0.17 1.2.7 13 10207 12.so.0.1.2.7 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5 1.0.18 10 10018 12.so.0.1.0.18 1.2.8 13 10208 12.so.0.1.2.8 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3 1.2.9beta4-11 13 10209 12.so.0.9[.0] 1.2.9rc1 13 10209 12.so.0.9[.0] 1.2.9 13 10209 12.so.0.9[.0] 1.2.10beta1-7 13 10210 12.so.0.10[.0] 1.2.10rc1-2 13 10210 12.so.0.10[.0] 1.2.10 13 10210 12.so.0.10[.0] 1.4.0beta1-6 14 10400 14.so.0.0[.0] 1.2.11beta1-4 13 10210 12.so.0.11[.0] 1.4.0beta7-8 14 10400 14.so.0.0[.0] 1.2.11 13 10211 12.so.0.11[.0] 1.2.12 13 10212 12.so.0.12[.0] 1.4.0beta9-14 14 10400 14.so.0.0[.0] 1.2.13 13 10213 12.so.0.13[.0] 1.4.0beta15-36 14 10400 14.so.0.0[.0] 1.4.0beta37-87 14 10400 14.so.14.0[.0] 1.4.0rc01 14 10400 14.so.14.0[.0] 1.4.0beta88-109 14 10400 14.so.14.0[.0] 1.4.0rc02-08 14 10400 14.so.14.0[.0] 1.4.0 14 10400 14.so.14.0[.0] 1.4.1beta01-03 14 10401 14.so.14.1[.0] 1.4.1rc01 14 10401 14.so.14.1[.0] 1.4.1beta04-12 14 10401 14.so.14.1[.0] 1.4.1 14 10401 14.so.14.1[.0] 1.4.2 14 10402 14.so.14.2[.0] 1.4.3 14 10403 14.so.14.3[.0] 1.4.4 14 10404 14.so.14.4[.0] 1.5.0beta01-58 15 10500 15.so.15.0[.0] 1.5.0rc01-07 15 10500 15.so.15.0[.0] 1.5.0 15 10500 15.so.15.0[.0] 1.5.1beta01-11 15 10501 15.so.15.1[.0] 1.5.1rc01-02 15 10501 15.so.15.1[.0] 1.5.1 15 10501 15.so.15.1[.0] 1.5.2beta01-03 15 10502 15.so.15.2[.0] 1.5.2rc01-03 15 10502 15.so.15.2[.0] 1.5.2 15 10502 15.so.15.2[.0]
Henceforth the source version will match the shared-library minorand patch numbers; the shared-library major version number will beused for changes in backward compatibility, as it is intended. ThePNG_PNGLIB_VER macro, which is not used within libpng but is availablefor applications, is an unsigned integer of the form xyyzz correspondingto the source version x.y.z (leading zeros in y and z). Beta versionswere given the previous public release number plus a letter, untilversion 1.0.6j; from then on they were given the upcoming publicrelease number plus "betaNN" or "rcN".
.SH "SEE ALSO".BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
.LP.IR libpng :.IPhttp://libpng.sourceforge.net (follow the [DOWNLOAD] link)http://www.libpng.org/pub/png
.LP.IR zlib :.IP(generally) at the same location as.I libpngor at.brftp://ftp.info-zip.org/pub/infozip/zlib
.LP.IR PNG specification: RFC 2083.IP(generally) at the same location as.I libpngor at.brftp://ds.internic.net/rfc/rfc2083.txt.bror (as a W3C Recommendation) at.brhttp://www.w3.org/TR/REC-png.html
.LPIn the case of any inconsistency between the PNG specificationand this library, the specification takes precedence.
.SH AUTHORSThis man page: Glenn Randers-Pehrson<glennrp at users.sourceforge.net>
The contributing authors would like to thank all those who helpedwith testing, bug fixes, and patience. This wouldn't have beenpossible without all of you.
Thanks to Frank J. T. Wojcik for helping with the documentation.
Libpng version 1.5.2 - March 31, 2011:Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
Supported by the PNG development group.brpng-mng-implement at lists.sf.net(subscription required; visitpng-mng-implement at lists.sourceforge.net (subscription required; visithttps://lists.sourceforge.net/lists/listinfo/png-mng-implementto subscribe).
.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
(This copy of the libpng notices is provided for your convenience. In case ofany discrepancy between this copy and the notices in the file png.h that isincluded in the libpng distribution, the latter shall prevail.)
If you modify libpng you may insert additional notices immediately followingthis sentence.
This code is released under the libpng license.
libpng versions 1.2.6, August 15, 2004, through 1.5.2, March 31, 2011, areCopyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and aredistributed according to the same disclaimer and license as libpng-1.2.5with the following individual added to the list of Contributing Authors
Cosmin Truta
libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, areCopyright (c) 2000-2002 Glenn Randers-Pehrson, and aredistributed according to the same disclaimer and license as libpng-1.0.6with the following individuals added to the list of Contributing Authors
Simon-Pierre Cadieux Eric S. Raymond Gilles Vollant
and with the following additions to the disclaimer:
There is no warranty against interference with your enjoyment of the library or against infringement. There is no warranty that our efforts or the library will fulfill any of your particular purposes or needs. This library is provided with all faults, and the entire risk of satisfactory quality, performance, accuracy, and effort is with the user.
libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, areCopyright (c) 1998, 1999 Glenn Randers-PehrsonDistributed according to the same disclaimer and license as libpng-0.96,with the following individuals added to the list of Contributing Authors:
Tom Lane Glenn Randers-Pehrson Willem van Schaik
libpng versions 0.89, June 1996, through 0.96, May 1997, areCopyright (c) 1996, 1997 Andreas DilgerDistributed according to the same disclaimer and license as libpng-0.88,with the following individuals added to the list of Contributing Authors:
John Bowler Kevin Bracey Sam Bushell Magnus Holmgren Greg Roelofs Tom Tanner
libpng versions 0.5, May 1995, through 0.88, January 1996, areCopyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
For the purposes of this copyright and license, "Contributing Authors"is defined as the following set of individuals:
Andreas Dilger Dave Martindale Guy Eric Schalnat Paul Schmidt Tim Wegner
The PNG Reference Library is supplied "AS IS". The Contributing Authorsand Group 42, Inc. disclaim all warranties, expressed or implied,including, without limitation, the warranties of merchantability and offitness for any purpose. The Contributing Authors and Group 42, Inc.assume no liability for direct, indirect, incidental, special, exemplary,or consequential damages, which may result from the use of the PNGReference Library, even if advised of the possibility of such damage.
Permission is hereby granted to use, copy, modify, and distribute thissource code, or portions hereof, for any purpose, without fee, subjectto the following restrictions:
1. The origin of this source code must not be misrepresented.
2. Altered versions must be plainly marked as such and must not be misrepresented as being the original source.
3. This Copyright notice may not be removed or altered from any source or altered source distribution.
The Contributing Authors and Group 42, Inc. specifically permit, withoutfee, and encourage the use of this source code as a component tosupporting the PNG file format in commercial products. If you use thissource code in a product, acknowledgment is not required but would beappreciated.
A "png_get_copyright" function is available, for convenient use in "about"boxes and the like:
printf("%s",png_get_copyright(NULL));
Also, the PNG logo (in PNG format, of course) is supplied in thefiles "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
Libpng is OSI Certified Open Source Software. OSI Certified Open Source is acertification mark of the Open Source Initiative.
Glenn Randers-Pehrsonglennrp at users.sourceforge.netMarch 31, 2011
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