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libpng.3
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.TH LIBPNG 3 "September 12, 2004"
.SH NAME
libpng \- Portable Network Graphics (PNG) Reference Library 1.2.7
.SH SYNOPSIS
\fI\fB
\fB#include <png.h>\fP
\fI\fB
\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
\fI\fB
\fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
\fI\fB
\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
\fI\fB
\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
\fI\fB
\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
\fI\fB
\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
\fI\fB
\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
\fI\fB
\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\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
\fI\fB
\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
\fI\fB
\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
\fI\fB
\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
\fI\fB
\fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
\fI\fB
\fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
\fI\fB
\fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
\fI\fB
\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
\fI\fB
\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
\fI\fB
\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
\fI\fB
\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
\fI\fB
\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
\fI\fB
\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_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
\fI\fB
\fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_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
\fI\fB
\fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
\fI\fB
\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
\fI\fB
\fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_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
\fI\fB
\fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_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
\fI\fB
\fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_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
\fI\fB
\fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
\fI\fB
\fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
\fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
\fI\fB
\fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_values\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
\fI\fB
\fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
\fI\fB
\fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
\fI\fB
\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
\fI\fB
\fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
\fI\fB
\fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
\fI\fB
\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
\fI\fB
\fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
\fI\fB
\fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
\fI\fB
\fBpng_voidp png_memcpy_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
\fI\fB
\fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
\fI\fB
\fBpng_voidp png_memset_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
\fI\fB
\fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_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
\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_destroy (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_infop \fIend_info_ptr\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
\fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBDEPRECATED: void png_read_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\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
\fB#if \fI!defined(PNG_1_0_X)
\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#endif
\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_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_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_dither (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_dither\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_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
\fI\fB
\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
\fI\fB
\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_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
\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_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \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
\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
\fI\fB
\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_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_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_fixed_point \fP\fIred\fP\fB, png_fixed_point \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, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \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 \fIintent\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 \fIintent\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_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\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_values\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_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_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
\fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\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_destroy (png_structp \fIpng_ptr\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
\fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
\fI\fB
\fBDEPRECATED: void png_write_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\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
\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 DESCRIPTION
The
.I libpng
library supports encoding, decoding, and various manipulations of
the Portable Network Graphics (PNG) format image files. It uses the
.IR zlib(3)
compression library.
Following is a copy of the libpng.txt file that accompanies libpng.
.SH LIBPNG.TXT
libpng.txt - A description on how to use and modify libpng
libpng version 1.2.7 - September 12, 2004
Updated and distributed by Glenn Randers-Pehrson
<glennrp@users.sourceforge.net>
Copyright (c) 1998-2004 Glenn Randers-Pehrson
For conditions of distribution and use, see copyright
notice in png.h.
based on:
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 this
file: introduction, structures, reading, writing, and modification and
configuration notes for various special platforms. In addition to this
file, example.c is a good starting point for using the library, as
it is heavily commented and should include everything most people
will need. We assume that libpng is already installed; see the
INSTALL file for instructions on how to install libpng.
Libpng was written as a companion to the PNG specification, as a way
of reducing the amount of time and effort it takes to support the PNG
file format in application programs.
The PNG specification (second edition), November 2003, is available as
a 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/>
The PNG-1.0 specification is available
as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
additional chunks are described in the special-purpose public chunks
documents at <http://www.libpng.org/pub/png/documents/>.
Other information
about PNG, and the latest version of libpng, can be found at the PNG home
page, <http://www.libpng.org/pub/png/>.
Most users will not have to modify the library significantly; advanced
users may want to modify it more. All attempts were made to make it as
complete as possible, while keeping the code easy to understand.
Currently, this library only supports C. Support for other languages
is being considered.
Libpng has been designed to handle multiple sessions at one time,
to be easily modifiable, to be portable to the vast majority of
machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
to use. The ultimate goal of libpng is to promote the acceptance of
the PNG file format in whatever way possible. While there is still
work to be done (see the TODO file), libpng should cover the
majority 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, can
be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
The zlib compression utility is a general purpose utility that is
useful 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 you
find the libpng source files.
Libpng is thread safe, provided the threads are using different
instances of the structures. Each thread should have its own
png_struct and png_info instances, and thus its own image.
Libpng does not protect itself against two threads using the
same instance of a structure. Note: thread safety may be defeated
by use of some of the MMX assembler code in pnggccrd.c, which is only
compiled when the user defines PNG_THREAD_UNSAFE_OK.
.SH II. Structures
There are two main structures that are important to libpng, png_struct
and png_info. The first, png_struct, is an internal structure that
will not, for the most part, be used by a user except as the first
variable passed to every libpng function call.
The png_info structure is designed to provide information about the
PNG file. At one time, the fields of png_info were intended to be
directly accessible to the user. However, this tended to cause problems
with applications using dynamically loaded libraries, and as a result
a set of interface functions for png_info (the png_get_*() and png_set_*()
functions) was developed. The fields of png_info are still available for
older applications, but it is suggested that applications use the new
interfaces if at all possible.
Applications that do make direct access to the members of png_struct (except
for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
and applications that make direct access to the members of png_info must
be recompiled if they were compiled or loaded with libpng version 1.0.6,
in which the members were in a different order. In version 1.0.7, the
members of the png_info structure reverted to the old order, as they were
in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
structures are going to be hidden, and the contents of the structures will
only be accessible through the png_get/png_set functions.
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>
.SH III. Reading
We'll now walk you through the possible functions to call when reading
in a PNG file sequentially, briefly explaining the syntax and purpose
of each one. See example.c and png.h for more detail. While
progressive reading is covered in the next section, you will still
need some of the functions discussed in this section to read a PNG
file.
.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, you
will also want to insure that you are, in fact, dealing with a PNG
file. 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 function
png_sig_cmp(), and it will return 0 if the bytes match the corresponding
bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
you pass in, the greater the accuracy of the prediction.
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 beginning
of 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 will
then only check the bytes (if any) that your program didn't read.
(*): If you are not using the standard I/O functions, you will need
to replace them with custom functions. See the discussion under
Customizing 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. In
order to ensure that the size of these structures is correct even with a
dynamically linked libpng, there are functions to initialize and
allocate the structures. We also pass the library version, optional
pointers to error handling functions, and a pointer to a data struct for
use by the error functions, if necessary (the pointer and functions can
be NULL if the default error handlers are to be used). See the section
on Changes to Libpng below regarding the old initialization functions.
The structure allocation functions quietly return NULL if they fail to
create 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,
define PNG_USER_MEM_SUPPORTED and use
png_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 error
handling and memory alloc/free functions.
When libpng encounters an error, it expects to longjmp back
to your routine. Therefore, you will need to call setjmp and pass
your png_jmpbuf(png_ptr). If you read the file from different
routines, you will need to update the jmpbuf field every time you enter
a new routine that will call a png_*() function.
See your documentation of setjmp/longjmp for your compiler for more
information on setjmp/longjmp. See the discussion on libpng error
handling in the Customizing Libpng section below for more information