1 .TH LIBPNG 3 "October 3, 2002"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.2.5
11 \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
15 \fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
19 \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
23 \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
27 \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
31 \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
35 \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
39 \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
43 \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
47 \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
51 \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
55 \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
59 \fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
63 \fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
67 \fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
71 \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
75 \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
79 \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
83 \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
87 \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
91 \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
95 \fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
99 \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
103 \fBpng_uint_32 png_get_asm_flags (png_structp \fIpng_ptr\fP\fB);\fP
107 \fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
111 \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
115 \fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
119 \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
123 \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
127 \fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
131 \fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
135 \fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
139 \fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
143 \fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
147 \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
151 \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
155 \fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
159 \fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
163 \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
167 \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
171 \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
175 \fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
179 \fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
183 \fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
187 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
191 \fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
195 \fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
199 \fBpng_byte png_get_mmx_bitdepth_threshold (png_structp \fIpng_ptr\fP\fB);\fP
203 \fBpng_uint_32 png_get_mmx_flagmask (int \fP\fIflag_select\fP\fB, int \fI*compilerID\fP\fB);\fP
207 \fBpng_uint_32 png_get_mmx_rowbytes_threshold (png_structp \fIpng_ptr\fP\fB);\fP
211 \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
215 \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
219 \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
223 \fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
227 \fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
231 \fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
235 \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
239 \fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
241 \fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
245 \fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
249 \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
253 \fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
257 \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
261 \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
265 \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
269 \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
273 \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
277 \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
281 \fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
285 \fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
289 \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
293 \fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
297 \fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
301 \fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
305 \fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
309 \fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
313 \fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
317 \fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
321 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
325 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
329 \fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
333 \fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
337 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
341 \fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
345 \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
349 \fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
353 \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
357 \fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
361 \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
365 \fBint png_mmx_support \fI(void\fP\fB);\fP
369 \fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
373 \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
377 \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
381 \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
385 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
389 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
393 \fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
397 \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
401 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
405 \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
409 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
413 \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
417 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
421 \fBpng_set_asm_flags (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIasm_flags\fP\fB);\fP
425 \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
429 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
433 \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
437 \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
441 \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
445 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
449 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
453 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
457 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
461 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
465 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
469 \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
473 \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
477 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
481 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
485 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
489 \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
493 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
497 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
501 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
505 \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
509 \fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
513 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
517 \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
521 \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
525 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
529 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
533 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
537 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
541 \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
545 \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
549 \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
553 \fBpng_set_mmx_thresholds (png_structp \fP\fIpng_ptr\fP\fB, png_byte \fP\fImmx_bitdepth_threshold\fP\fB, png_uint_32 \fImmx_rowbytes_threshold\fP\fB);\fP
557 \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
561 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
565 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
569 \fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
573 \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
577 \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
581 \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
585 \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
589 \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
593 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
597 \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
601 \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
605 \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
609 \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
613 \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
617 \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
621 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
625 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
629 \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
633 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
637 \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
641 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
645 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
649 \fBvoid png_set_strip_error_numbers (png_structp \fIpng_ptr,
651 \fBpng_uint_32 \fIstrip_mode\fP\fB);\fP
655 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
659 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
663 \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
667 \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
671 \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
675 \fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
679 \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
683 \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
687 \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
691 \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
695 \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
699 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
703 \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
707 \fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
711 \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
715 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
719 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
723 \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
727 \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
731 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
735 \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
739 \fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
743 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
747 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
751 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
755 \fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
759 \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
763 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
767 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
771 \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
775 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
779 \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
786 library supports encoding, decoding, and various manipulations of
787 the Portable Network Graphics (PNG) format image files. It uses the
790 Following is a copy of the libpng.txt file that accompanies libpng.
792 libpng.txt - A description on how to use and modify libpng
794 libpng version 1.2.5 - October 3, 2002
795 Updated and distributed by Glenn Randers-Pehrson
796 <randeg@alum.rpi.edu>
797 Copyright (c) 1998-2002 Glenn Randers-Pehrson
798 For conditions of distribution and use, see copyright
803 libpng 1.0 beta 6 version 0.96 May 28, 1997
804 Updated and distributed by Andreas Dilger
805 Copyright (c) 1996, 1997 Andreas Dilger
807 libpng 1.0 beta 2 - version 0.88 January 26, 1996
808 For conditions of distribution and use, see copyright
809 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
810 Schalnat, Group 42, Inc.
812 Updated/rewritten per request in the libpng FAQ
813 Copyright (c) 1995, 1996 Frank J. T. Wojcik
814 December 18, 1995 & January 20, 1996
818 This file describes how to use and modify the PNG reference library
819 (known as libpng) for your own use. There are five sections to this
820 file: introduction, structures, reading, writing, and modification and
821 configuration notes for various special platforms. In addition to this
822 file, example.c is a good starting point for using the library, as
823 it is heavily commented and should include everything most people
824 will need. We assume that libpng is already installed; see the
825 INSTALL file for instructions on how to install libpng.
827 Libpng was written as a companion to the PNG specification, as a way
828 of reducing the amount of time and effort it takes to support the PNG
829 file format in application programs.
831 The PNG-1.2 specification is available at <http://www.libpng.org/pub/png>
832 and at <ftp://ftp.uu.net/graphics/png/documents/>.
834 The PNG-1.0 specification is available
835 as RFC 2083 <ftp://ftp.uu.net/graphics/png/documents/> and as a
836 W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
837 additional chunks are described in the special-purpose public chunks
838 documents at <ftp://ftp.uu.net/graphics/png/documents/>.
841 about PNG, and the latest version of libpng, can be found at the PNG home
842 page, <http://www.libpng.org/pub/png/>
843 and at <ftp://ftp.uu.net/graphics/png/>.
845 Most users will not have to modify the library significantly; advanced
846 users may want to modify it more. All attempts were made to make it as
847 complete as possible, while keeping the code easy to understand.
848 Currently, this library only supports C. Support for other languages
851 Libpng has been designed to handle multiple sessions at one time,
852 to be easily modifiable, to be portable to the vast majority of
853 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
854 to use. The ultimate goal of libpng is to promote the acceptance of
855 the PNG file format in whatever way possible. While there is still
856 work to be done (see the TODO file), libpng should cover the
857 majority of the needs of its users.
859 Libpng uses zlib for its compression and decompression of PNG files.
860 Further information about zlib, and the latest version of zlib, can
861 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
862 The zlib compression utility is a general purpose utility that is
863 useful for more than PNG files, and can be used without libpng.
864 See the documentation delivered with zlib for more details.
865 You can usually find the source files for the zlib utility wherever you
866 find the libpng source files.
868 Libpng is thread safe, provided the threads are using different
869 instances of the structures. Each thread should have its own
870 png_struct and png_info instances, and thus its own image.
871 Libpng does not protect itself against two threads using the
872 same instance of a structure. Note: thread safety may be defeated
873 by use of some of the MMX assembler code in pnggccrd.c, which is only
874 compiled when the user defines PNG_THREAD_UNSAFE_OK.
879 There are two main structures that are important to libpng, png_struct
880 and png_info. The first, png_struct, is an internal structure that
881 will not, for the most part, be used by a user except as the first
882 variable passed to every libpng function call.
884 The png_info structure is designed to provide information about the
885 PNG file. At one time, the fields of png_info were intended to be
886 directly accessible to the user. However, this tended to cause problems
887 with applications using dynamically loaded libraries, and as a result
888 a set of interface functions for png_info (the png_get_*() and png_set_*()
889 functions) was developed. The fields of png_info are still available for
890 older applications, but it is suggested that applications use the new
891 interfaces if at all possible.
893 Applications that do make direct access to the members of png_struct (except
894 for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
895 and applications that make direct access to the members of png_info must
896 be recompiled if they were compiled or loaded with libpng version 1.0.6,
897 in which the members were in a different order. In version 1.0.7, the
898 members of the png_info structure reverted to the old order, as they were
899 in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
900 structures are going to be hidden, and the contents of the structures will
901 only be accessible through the png_get/png_set functions.
903 The png.h header file is an invaluable reference for programming with libpng.
904 And while I'm on the topic, make sure you include the libpng header file:
910 We'll now walk you through the possible functions to call when reading
911 in a PNG file sequentially, briefly explaining the syntax and purpose
912 of each one. See example.c and png.h for more detail. While
913 progressive reading is covered in the next section, you will still
914 need some of the functions discussed in this section to read a PNG
919 You will want to do the I/O initialization(*) before you get into libpng,
920 so if it doesn't work, you don't have much to undo. Of course, you
921 will also want to insure that you are, in fact, dealing with a PNG
922 file. Libpng provides a simple check to see if a file is a PNG file.
923 To use it, pass in the first 1 to 8 bytes of the file to the function
924 png_sig_cmp(), and it will return 0 if the bytes match the corresponding
925 bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
926 you pass in, the greater the accuracy of the prediction.
928 If you are intending to keep the file pointer open for use in libpng,
929 you must ensure you don't read more than 8 bytes from the beginning
930 of the file, and you also have to make a call to png_set_sig_bytes_read()
931 with the number of bytes you read from the beginning. Libpng will
932 then only check the bytes (if any) that your program didn't read.
934 (*): If you are not using the standard I/O functions, you will need
935 to replace them with custom functions. See the discussion under
939 FILE *fp = fopen(file_name, "rb");
944 fread(header, 1, number, fp);
945 is_png = !png_sig_cmp(header, 0, number);
952 Next, png_struct and png_info need to be allocated and initialized. In
953 order to ensure that the size of these structures is correct even with a
954 dynamically linked libpng, there are functions to initialize and
955 allocate the structures. We also pass the library version, optional
956 pointers to error handling functions, and a pointer to a data struct for
957 use by the error functions, if necessary (the pointer and functions can
958 be NULL if the default error handlers are to be used). See the section
959 on Changes to Libpng below regarding the old initialization functions.
960 The structure allocation functions quietly return NULL if they fail to
961 create the structure, so your application should check for that.
963 png_structp png_ptr = png_create_read_struct
964 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
965 user_error_fn, user_warning_fn);
969 png_infop info_ptr = png_create_info_struct(png_ptr);
972 png_destroy_read_struct(&png_ptr,
973 (png_infopp)NULL, (png_infopp)NULL);
977 png_infop end_info = png_create_info_struct(png_ptr);
980 png_destroy_read_struct(&png_ptr, &info_ptr,
985 If you want to use your own memory allocation routines,
986 define PNG_USER_MEM_SUPPORTED and use
987 png_create_read_struct_2() instead of png_create_read_struct():
989 png_structp png_ptr = png_create_read_struct_2
990 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
991 user_error_fn, user_warning_fn, (png_voidp)
992 user_mem_ptr, user_malloc_fn, user_free_fn);
994 The error handling routines passed to png_create_read_struct()
995 and the memory alloc/free routines passed to png_create_struct_2()
996 are only necessary if you are not using the libpng supplied error
997 handling and memory alloc/free functions.
999 When libpng encounters an error, it expects to longjmp back
1000 to your routine. Therefore, you will need to call setjmp and pass
1001 your png_jmpbuf(png_ptr). If you read the file from different
1002 routines, you will need to update the jmpbuf field every time you enter
1003 a new routine that will call a png_*() function.
1005 See your documentation of setjmp/longjmp for your compiler for more
1006 information on setjmp/longjmp. See the discussion on libpng error
1007 handling in the Customizing Libpng section below for more information
1008 on the libpng error handling. If an error occurs, and libpng longjmp's
1009 back to your setjmp, you will want to call png_destroy_read_struct() to
1012 if (setjmp(png_jmpbuf(png_ptr)))
1014 png_destroy_read_struct(&png_ptr, &info_ptr,
1020 If you would rather avoid the complexity of setjmp/longjmp issues,
1021 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
1022 errors will result in a call to PNG_ABORT() which defaults to abort().
1024 Now you need to set up the input code. The default for libpng is to
1025 use the C function fread(). If you use this, you will need to pass a
1026 valid FILE * in the function png_init_io(). Be sure that the file is
1027 opened in binary mode. If you wish to handle reading data in another
1028 way, you need not call the png_init_io() function, but you must then
1029 implement the libpng I/O methods discussed in the Customizing Libpng
1032 png_init_io(png_ptr, fp);
1034 If you had previously opened the file and read any of the signature from
1035 the beginning in order to see if this was a PNG file, you need to let
1036 libpng know that there are some bytes missing from the start of the file.
1038 png_set_sig_bytes(png_ptr, number);
1040 .SS Setting up callback code
1042 You can set up a callback function to handle any unknown chunks in the
1043 input stream. You must supply the function
1045 read_chunk_callback(png_ptr ptr,
1046 png_unknown_chunkp chunk);
1048 /* The unknown chunk structure contains your
1053 /* Note that libpng has already taken care of
1056 /* put your code here. Return one of the
1059 return (-n); /* chunk had an error */
1060 return (0); /* did not recognize */
1061 return (n); /* success */
1064 (You can give your function another name that you like instead of
1065 "read_chunk_callback")
1067 To inform libpng about your function, use
1069 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1070 read_chunk_callback);
1072 This names not only the callback function, but also a user pointer that
1073 you can retrieve with
1075 png_get_user_chunk_ptr(png_ptr);
1077 At this point, you can set up a callback function that will be
1078 called after each row has been read, which you can use to control
1079 a progress meter or the like. It's demonstrated in pngtest.c.
1080 You must supply a function
1082 void read_row_callback(png_ptr ptr, png_uint_32 row,
1085 /* put your code here */
1088 (You can give it another name that you like instead of "read_row_callback")
1090 To inform libpng about your function, use
1092 png_set_read_status_fn(png_ptr, read_row_callback);
1094 .SS Unknown-chunk handling
1096 Now you get to set the way the library processes unknown chunks in the
1097 input PNG stream. Both known and unknown chunks will be read. Normal
1098 behavior is that known chunks will be parsed into information in
1099 various info_ptr members; unknown chunks will be discarded. To change
1102 png_set_keep_unknown_chunks(png_ptr, info_ptr, keep,
1103 chunk_list, num_chunks);
1104 keep - 0: do not keep
1105 1: keep only if safe-to-copy
1106 2: keep even if unsafe-to-copy
1107 chunk_list - list of chunks affected (a byte string,
1108 five bytes per chunk, NULL or '\0' if
1110 num_chunks - number of chunks affected; if 0, all
1111 unknown chunks are affected
1113 Unknown chunks declared in this way will be saved as raw data onto a
1114 list of png_unknown_chunk structures. If a chunk that is normally
1115 known to libpng is named in the list, it will be handled as unknown,
1116 according to the "keep" directive. If a chunk is named in successive
1117 instances of png_set_keep_unknown_chunks(), the final instance will
1120 .SS The high-level read interface
1122 At this point there are two ways to proceed; through the high-level
1123 read interface, or through a sequence of low-level read operations.
1124 You can use the high-level interface if (a) you are willing to read
1125 the entire image into memory, and (b) the input transformations
1126 you want to do are limited to the following set:
1128 PNG_TRANSFORM_IDENTITY No transformation
1129 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1131 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1132 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1134 PNG_TRANSFORM_PACKSWAP Change order of packed
1136 PNG_TRANSFORM_EXPAND Perform set_expand()
1137 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1138 PNG_TRANSFORM_SHIFT Normalize pixels to the
1140 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1142 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1144 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1146 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1148 (This excludes setting a background color, doing gamma transformation,
1149 dithering, and setting filler.) If this is the case, simply do this:
1151 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1153 where png_transforms is an integer containing the logical OR of
1154 some set of transformation flags. This call is equivalent to png_read_info(),
1155 followed the set of transformations indicated by the transform mask,
1156 then png_read_image(), and finally png_read_end().
1158 (The final parameter of this call is not yet used. Someday it might point
1159 to transformation parameters required by some future input transform.)
1161 After you have called png_read_png(), you can retrieve the image data
1164 row_pointers = png_get_rows(png_ptr, info_ptr);
1166 where row_pointers is an array of pointers to the pixel data for each row:
1168 png_bytep row_pointers[height];
1170 If you know your image size and pixel size ahead of time, you can allocate
1171 row_pointers prior to calling png_read_png() with
1173 row_pointers = png_malloc(png_ptr,
1174 height*sizeof(png_bytep));
1175 for (int i=0; i<height, i++)
1176 row_pointers[i]=png_malloc(png_ptr,
1178 png_set_rows(png_ptr, info_ptr, &row_pointers);
1180 Alternatively you could allocate your image in one big block and define
1181 row_pointers[i] to point into the proper places in your block.
1183 If you use png_set_rows(), the application is responsible for freeing
1184 row_pointers (and row_pointers[i], if they were separately allocated).
1186 If you don't allocate row_pointers ahead of time, png_read_png() will
1187 do it, and it'll be free'ed when you call png_destroy_*().
1189 .SS The low-level read interface
1191 If you are going the low-level route, you are now ready to read all
1192 the file information up to the actual image data. You do this with a
1193 call to png_read_info().
1195 png_read_info(png_ptr, info_ptr);
1197 This will process all chunks up to but not including the image data.
1199 .SS Querying the info structure
1201 Functions are used to get the information from the info_ptr once it
1202 has been read. Note that these fields may not be completely filled
1203 in until png_read_end() has read the chunk data following the image.
1205 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1206 &bit_depth, &color_type, &interlace_type,
1207 &compression_type, &filter_method);
1209 width - holds the width of the image
1210 in pixels (up to 2^31).
1211 height - holds the height of the image
1212 in pixels (up to 2^31).
1213 bit_depth - holds the bit depth of one of the
1214 image channels. (valid values are
1215 1, 2, 4, 8, 16 and depend also on
1216 the color_type. See also
1217 significant bits (sBIT) below).
1218 color_type - describes which color/alpha channels
1221 (bit depths 1, 2, 4, 8, 16)
1222 PNG_COLOR_TYPE_GRAY_ALPHA
1224 PNG_COLOR_TYPE_PALETTE
1225 (bit depths 1, 2, 4, 8)
1228 PNG_COLOR_TYPE_RGB_ALPHA
1231 PNG_COLOR_MASK_PALETTE
1232 PNG_COLOR_MASK_COLOR
1233 PNG_COLOR_MASK_ALPHA
1235 filter_method - (must be PNG_FILTER_TYPE_BASE
1236 for PNG 1.0, and can also be
1237 PNG_INTRAPIXEL_DIFFERENCING if
1238 the PNG datastream is embedded in
1239 a MNG-1.0 datastream)
1240 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1242 interlace_type - (PNG_INTERLACE_NONE or
1243 PNG_INTERLACE_ADAM7)
1244 Any or all of interlace_type, compression_type, of
1245 filter_method can be NULL if you are
1246 not interested in their values.
1248 channels = png_get_channels(png_ptr, info_ptr);
1249 channels - number of channels of info for the
1250 color type (valid values are 1 (GRAY,
1251 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1252 4 (RGB_ALPHA or RGB + filler byte))
1253 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1254 rowbytes - number of bytes needed to hold a row
1256 signature = png_get_signature(png_ptr, info_ptr);
1257 signature - holds the signature read from the
1258 file (if any). The data is kept in
1259 the same offset it would be if the
1260 whole signature were read (i.e. if an
1261 application had already read in 4
1262 bytes of signature before starting
1263 libpng, the remaining 4 bytes would
1264 be in signature[4] through signature[7]
1265 (see png_set_sig_bytes())).
1268 width = png_get_image_width(png_ptr,
1270 height = png_get_image_height(png_ptr,
1272 bit_depth = png_get_bit_depth(png_ptr,
1274 color_type = png_get_color_type(png_ptr,
1276 filter_method = png_get_filter_type(png_ptr,
1278 compression_type = png_get_compression_type(png_ptr,
1280 interlace_type = png_get_interlace_type(png_ptr,
1284 These are also important, but their validity depends on whether the chunk
1285 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1286 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1287 data has been read, or zero if it is missing. The parameters to the
1288 png_get_<chunk> are set directly if they are simple data types, or a pointer
1289 into the info_ptr is returned for any complex types.
1291 png_get_PLTE(png_ptr, info_ptr, &palette,
1293 palette - the palette for the file
1294 (array of png_color)
1295 num_palette - number of entries in the palette
1297 png_get_gAMA(png_ptr, info_ptr, &gamma);
1298 gamma - the gamma the file is written
1301 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1302 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1303 The presence of the sRGB chunk
1304 means that the pixel data is in the
1305 sRGB color space. This chunk also
1306 implies specific values of gAMA and
1309 png_get_iCCP(png_ptr, info_ptr, &name,
1310 &compression_type, &profile, &proflen);
1311 name - The profile name.
1312 compression - The compression type; always
1313 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1314 You may give NULL to this argument to
1316 profile - International Color Consortium color
1317 profile data. May contain NULs.
1318 proflen - length of profile data in bytes.
1320 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1321 sig_bit - the number of significant bits for
1322 (PNG_INFO_sBIT) each of the gray,
1323 red, green, and blue channels,
1324 whichever are appropriate for the
1325 given color type (png_color_16)
1327 png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
1329 trans - array of transparent entries for
1330 palette (PNG_INFO_tRNS)
1331 trans_values - graylevel or color sample values of
1332 the single transparent color for
1333 non-paletted images (PNG_INFO_tRNS)
1334 num_trans - number of transparent entries
1337 png_get_hIST(png_ptr, info_ptr, &hist);
1339 hist - histogram of palette (array of
1342 png_get_tIME(png_ptr, info_ptr, &mod_time);
1343 mod_time - time image was last modified
1346 png_get_bKGD(png_ptr, info_ptr, &background);
1347 background - background color (PNG_VALID_bKGD)
1348 valid 16-bit red, green and blue
1349 values, regardless of color_type
1351 num_comments = png_get_text(png_ptr, info_ptr,
1352 &text_ptr, &num_text);
1353 num_comments - number of comments
1354 text_ptr - array of png_text holding image
1356 text_ptr[i].compression - type of compression used
1357 on "text" PNG_TEXT_COMPRESSION_NONE
1358 PNG_TEXT_COMPRESSION_zTXt
1359 PNG_ITXT_COMPRESSION_NONE
1360 PNG_ITXT_COMPRESSION_zTXt
1361 text_ptr[i].key - keyword for comment. Must contain
1363 text_ptr[i].text - text comments for current
1364 keyword. Can be empty.
1365 text_ptr[i].text_length - length of text string,
1366 after decompression, 0 for iTXt
1367 text_ptr[i].itxt_length - length of itxt string,
1368 after decompression, 0 for tEXt/zTXt
1369 text_ptr[i].lang - language of comment (empty
1370 string for unknown).
1371 text_ptr[i].lang_key - keyword in UTF-8
1372 (empty string for unknown).
1373 num_text - number of comments (same as
1374 num_comments; you can put NULL here
1375 to avoid the duplication)
1376 Note while png_set_text() will accept text, language,
1377 and translated keywords that can be NULL pointers, the
1378 structure returned by png_get_text will always contain
1379 regular zero-terminated C strings. They might be
1380 empty strings but they will never be NULL pointers.
1382 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1384 palette_ptr - array of palette structures holding
1385 contents of one or more sPLT chunks
1387 num_spalettes - number of sPLT chunks read.
1389 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1391 offset_x - positive offset from the left edge
1393 offset_y - positive offset from the top edge
1395 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1397 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1399 res_x - pixels/unit physical resolution in
1401 res_y - pixels/unit physical resolution in
1403 unit_type - PNG_RESOLUTION_UNKNOWN,
1404 PNG_RESOLUTION_METER
1406 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1408 unit - physical scale units (an integer)
1409 width - width of a pixel in physical scale units
1410 height - height of a pixel in physical scale units
1411 (width and height are doubles)
1413 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1415 unit - physical scale units (an integer)
1416 width - width of a pixel in physical scale units
1417 height - height of a pixel in physical scale units
1418 (width and height are strings like "2.54")
1420 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1421 info_ptr, &unknowns)
1422 unknowns - array of png_unknown_chunk
1423 structures holding unknown chunks
1424 unknowns[i].name - name of unknown chunk
1425 unknowns[i].data - data of unknown chunk
1426 unknowns[i].size - size of unknown chunk's data
1427 unknowns[i].location - position of chunk in file
1429 The value of "i" corresponds to the order in which the
1430 chunks were read from the PNG file or inserted with the
1431 png_set_unknown_chunks() function.
1433 The data from the pHYs chunk can be retrieved in several convenient
1436 res_x = png_get_x_pixels_per_meter(png_ptr,
1438 res_y = png_get_y_pixels_per_meter(png_ptr,
1440 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1442 res_x = png_get_x_pixels_per_inch(png_ptr,
1444 res_y = png_get_y_pixels_per_inch(png_ptr,
1446 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1448 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1451 (Each of these returns 0 [signifying "unknown"] if
1452 the data is not present or if res_x is 0;
1453 res_x_and_y is 0 if res_x != res_y)
1455 The data from the oFFs chunk can be retrieved in several convenient
1458 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1459 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1460 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1461 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1463 (Each of these returns 0 [signifying "unknown" if both
1464 x and y are 0] if the data is not present or if the
1465 chunk is present but the unit is the pixel)
1467 For more information, see the png_info definition in png.h and the
1468 PNG specification for chunk contents. Be careful with trusting
1469 rowbytes, as some of the transformations could increase the space
1470 needed to hold a row (expand, filler, gray_to_rgb, etc.).
1471 See png_read_update_info(), below.
1473 A quick word about text_ptr and num_text. PNG stores comments in
1474 keyword/text pairs, one pair per chunk, with no limit on the number
1475 of text chunks, and a 2^31 byte limit on their size. While there are
1476 suggested keywords, there is no requirement to restrict the use to these
1477 strings. It is strongly suggested that keywords and text be sensible
1478 to humans (that's the point), so don't use abbreviations. Non-printing
1479 symbols are not allowed. See the PNG specification for more details.
1480 There is also no requirement to have text after the keyword.
1482 Keywords should be limited to 79 Latin-1 characters without leading or
1483 trailing spaces, but non-consecutive spaces are allowed within the
1484 keyword. It is possible to have the same keyword any number of times.
1485 The text_ptr is an array of png_text structures, each holding a
1486 pointer to a language string, a pointer to a keyword and a pointer to
1487 a text string. The text string, language code, and translated
1488 keyword may be empty or NULL pointers. The keyword/text
1489 pairs are put into the array in the order that they are received.
1490 However, some or all of the text chunks may be after the image, so, to
1491 make sure you have read all the text chunks, don't mess with these
1492 until after you read the stuff after the image. This will be
1493 mentioned again below in the discussion that goes with png_read_end().
1495 .SS Input transformations
1497 After you've read the header information, you can set up the library
1498 to handle any special transformations of the image data. The various
1499 ways to transform the data will be described in the order that they
1500 should occur. This is important, as some of these change the color
1501 type and/or bit depth of the data, and some others only work on
1502 certain color types and bit depths. Even though each transformation
1503 checks to see if it has data that it can do something with, you should
1504 make sure to only enable a transformation if it will be valid for the
1505 data. For example, don't swap red and blue on grayscale data.
1507 The colors used for the background and transparency values should be
1508 supplied in the same format/depth as the current image data. They
1509 are stored in the same format/depth as the image data in a bKGD or tRNS
1510 chunk, so this is what libpng expects for this data. The colors are
1511 transformed to keep in sync with the image data when an application
1512 calls the png_read_update_info() routine (see below).
1514 Data will be decoded into the supplied row buffers packed into bytes
1515 unless the library has been told to transform it into another format.
1516 For example, 4 bit/pixel paletted or grayscale data will be returned
1517 2 pixels/byte with the leftmost pixel in the high-order bits of the
1518 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1519 in RGB RGB RGB format unless png_set_filler() is called to insert filler
1520 bytes, either before or after each RGB triplet. 16-bit RGB data will
1521 be returned RRGGBB RRGGBB, with the most significant byte of the color
1522 value first, unless png_set_strip_16() is called to transform it to
1523 regular RGB RGB triplets, or png_set_filler() is called to insert
1524 filler bytes, either before or after each RRGGBB triplet. Similarly,
1525 8-bit or 16-bit grayscale data can be modified with png_set_filler()
1526 or png_set_strip_16().
1528 The following code transforms grayscale images of less than 8 to 8 bits,
1529 changes paletted images to RGB, and adds a full alpha channel if there is
1530 transparency information in a tRNS chunk. This is most useful on
1531 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1532 viewing application that wishes to treat all images in the same way.
1534 if (color_type == PNG_COLOR_TYPE_PALETTE)
1535 png_set_palette_to_rgb(png_ptr);
1537 if (color_type == PNG_COLOR_TYPE_GRAY &&
1538 bit_depth < 8) png_set_gray_1_2_4_to_8(png_ptr);
1540 if (png_get_valid(png_ptr, info_ptr,
1541 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1543 These three functions are actually aliases for png_set_expand(), added
1544 in libpng version 1.0.4, with the function names expanded to improve code
1545 readability. In some future version they may actually do different
1548 PNG can have files with 16 bits per channel. If you only can handle
1549 8 bits per channel, this will strip the pixels down to 8 bit.
1551 if (bit_depth == 16)
1552 png_set_strip_16(png_ptr);
1554 If, for some reason, you don't need the alpha channel on an image,
1555 and you want to remove it rather than combining it with the background
1556 (but the image author certainly had in mind that you *would* combine
1557 it with the background, so that's what you should probably do):
1559 if (color_type & PNG_COLOR_MASK_ALPHA)
1560 png_set_strip_alpha(png_ptr);
1562 In PNG files, the alpha channel in an image
1563 is the level of opacity. If you need the alpha channel in an image to
1564 be the level of transparency instead of opacity, you can invert the
1565 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1566 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1567 images) is fully transparent, with
1569 png_set_invert_alpha(png_ptr);
1571 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1572 they can, resulting in, for example, 8 pixels per byte for 1 bit
1573 files. This code expands to 1 pixel per byte without changing the
1574 values of the pixels:
1577 png_set_packing(png_ptr);
1579 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1580 stored in a PNG image have been "scaled" or "shifted" up to the next
1581 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
1582 8 bits/sample in the range [0, 255]). However, it is also possible to
1583 convert the PNG pixel data back to the original bit depth of the image.
1584 This call reduces the pixels back down to the original bit depth:
1586 png_color_8p sig_bit;
1588 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1589 png_set_shift(png_ptr, sig_bit);
1591 PNG files store 3-color pixels in red, green, blue order. This code
1592 changes the storage of the pixels to blue, green, red:
1594 if (color_type == PNG_COLOR_TYPE_RGB ||
1595 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1596 png_set_bgr(png_ptr);
1598 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1599 into 4 or 8 bytes for windowing systems that need them in this format:
1601 if (color_type == PNG_COLOR_TYPE_RGB)
1602 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1604 where "filler" is the 8 or 16-bit number to fill with, and the location is
1605 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1606 you want the filler before the RGB or after. This transformation
1607 does not affect images that already have full alpha channels. To add an
1608 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1609 will generate RGBA pixels.
1611 If you are reading an image with an alpha channel, and you need the
1612 data as ARGB instead of the normal PNG format RGBA:
1614 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1615 png_set_swap_alpha(png_ptr);
1617 For some uses, you may want a grayscale image to be represented as
1618 RGB. This code will do that conversion:
1620 if (color_type == PNG_COLOR_TYPE_GRAY ||
1621 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1622 png_set_gray_to_rgb(png_ptr);
1624 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1627 if (color_type == PNG_COLOR_TYPE_RGB ||
1628 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1629 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1630 int red_weight, int green_weight);
1632 error_action = 1: silently do the conversion
1633 error_action = 2: issue a warning if the original
1634 image has any pixel where
1635 red != green or red != blue
1636 error_action = 3: issue an error and abort the
1637 conversion if the original
1638 image has any pixel where
1639 red != green or red != blue
1641 red_weight: weight of red component times 100000
1642 green_weight: weight of green component times 100000
1643 If either weight is negative, default
1644 weights (21268, 71514) are used.
1646 If you have set error_action = 1 or 2, you can
1647 later check whether the image really was gray, after processing
1648 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1649 It will return a png_byte that is zero if the image was gray or
1650 1 if there were any non-gray pixels. bKGD and sBIT data
1651 will be silently converted to grayscale, using the green channel
1652 data, regardless of the error_action setting.
1654 With red_weight+green_weight<=100000,
1655 the normalized graylevel is computed:
1657 int rw = red_weight * 65536;
1658 int gw = green_weight * 65536;
1659 int bw = 65536 - (rw + gw);
1660 gray = (rw*red + gw*green + bw*blue)/65536;
1662 The default values approximate those recommended in the Charles
1663 Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1664 Copyright (c) 1998-01-04 Charles Poynton poynton@inforamp.net
1666 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1668 Libpng approximates this with
1670 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1672 which can be expressed with integers as
1674 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1676 The calculation is done in a linear colorspace, if the image gamma
1679 If you have a grayscale and you are using png_set_expand_depth(),
1680 png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1681 a higher bit-depth, you must either supply the background color as a gray
1682 value at the original file bit-depth (need_expand = 1) or else supply the
1683 background color as an RGB triplet at the final, expanded bit depth
1684 (need_expand = 0). Similarly, if you are reading a paletted image, you
1685 must either supply the background color as a palette index (need_expand = 1)
1686 or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1688 png_color_16 my_background;
1689 png_color_16p image_background;
1691 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1692 png_set_background(png_ptr, image_background,
1693 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1695 png_set_background(png_ptr, &my_background,
1696 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1698 The png_set_background() function tells libpng to composite images
1699 with alpha or simple transparency against the supplied background
1700 color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1701 you may use this color, or supply another color more suitable for
1702 the current display (e.g., the background color from a web page). You
1703 need to tell libpng whether the color is in the gamma space of the
1704 display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1705 (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1706 that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1707 know why anyone would use this, but it's here).
1709 To properly display PNG images on any kind of system, the application needs
1710 to know what the display gamma is. Ideally, the user will know this, and
1711 the application will allow them to set it. One method of allowing the user
1712 to set the display gamma separately for each system is to check for a
1713 SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1716 Note that display_gamma is the overall gamma correction required to produce
1717 pleasing results, which depends on the lighting conditions in the surrounding
1718 environment. In a dim or brightly lit room, no compensation other than
1719 the physical gamma exponent of the monitor is needed, while in a dark room
1720 a slightly smaller exponent is better.
1722 double gamma, screen_gamma;
1724 if (/* We have a user-defined screen
1727 screen_gamma = user_defined_screen_gamma;
1729 /* One way that applications can share the same
1730 screen gamma value */
1731 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1734 screen_gamma = (double)atof(gamma_str);
1736 /* If we don't have another value */
1739 screen_gamma = 2.2; /* A good guess for a
1740 PC monitor in a bright office or a dim room */
1741 screen_gamma = 2.0; /* A good guess for a
1742 PC monitor in a dark room */
1743 screen_gamma = 1.7 or 1.0; /* A good
1744 guess for Mac systems */
1747 The png_set_gamma() function handles gamma transformations of the data.
1748 Pass both the file gamma and the current screen_gamma. If the file does
1749 not have a gamma value, you can pass one anyway if you have an idea what
1750 it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1751 that file gammas are inverted from screen gammas. See the discussions
1752 on gamma in the PNG specification for an excellent description of what
1753 gamma is, and why all applications should support it. It is strongly
1754 recommended that PNG viewers support gamma correction.
1756 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1757 png_set_gamma(png_ptr, screen_gamma, gamma);
1759 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1761 If you need to reduce an RGB file to a paletted file, or if a paletted
1762 file has more entries then will fit on your screen, png_set_dither()
1763 will do that. Note that this is a simple match dither that merely
1764 finds the closest color available. This should work fairly well with
1765 optimized palettes, and fairly badly with linear color cubes. If you
1766 pass a palette that is larger then maximum_colors, the file will
1767 reduce the number of colors in the palette so it will fit into
1768 maximum_colors. If there is a histogram, it will use it to make
1769 more intelligent choices when reducing the palette. If there is no
1770 histogram, it may not do as good a job.
1772 if (color_type & PNG_COLOR_MASK_COLOR)
1774 if (png_get_valid(png_ptr, info_ptr,
1777 png_uint_16p histogram = NULL;
1779 png_get_hIST(png_ptr, info_ptr,
1781 png_set_dither(png_ptr, palette, num_palette,
1782 max_screen_colors, histogram, 1);
1786 png_color std_color_cube[MAX_SCREEN_COLORS] =
1789 png_set_dither(png_ptr, std_color_cube,
1790 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1795 PNG files describe monochrome as black being zero and white being one.
1796 The following code will reverse this (make black be one and white be
1799 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1800 png_set_invert_mono(png_ptr);
1802 This function can also be used to invert grayscale and gray-alpha images:
1804 if (color_type == PNG_COLOR_TYPE_GRAY ||
1805 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1806 png_set_invert_mono(png_ptr);
1808 PNG files store 16 bit pixels in network byte order (big-endian,
1809 ie. most significant bits first). This code changes the storage to the
1810 other way (little-endian, i.e. least significant bits first, the
1811 way PCs store them):
1813 if (bit_depth == 16)
1814 png_set_swap(png_ptr);
1816 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1817 need to change the order the pixels are packed into bytes, you can use:
1820 png_set_packswap(png_ptr);
1822 Finally, you can write your own transformation function if none of
1823 the existing ones meets your needs. This is done by setting a callback
1826 png_set_read_user_transform_fn(png_ptr,
1829 You must supply the function
1831 void read_transform_fn(png_ptr ptr, row_info_ptr
1832 row_info, png_bytep data)
1834 See pngtest.c for a working example. Your function will be called
1835 after all of the other transformations have been processed.
1837 You can also set up a pointer to a user structure for use by your
1838 callback function, and you can inform libpng that your transform
1839 function will change the number of channels or bit depth with the
1842 png_set_user_transform_info(png_ptr, user_ptr,
1843 user_depth, user_channels);
1845 The user's application, not libpng, is responsible for allocating and
1846 freeing any memory required for the user structure.
1848 You can retrieve the pointer via the function
1849 png_get_user_transform_ptr(). For example:
1851 voidp read_user_transform_ptr =
1852 png_get_user_transform_ptr(png_ptr);
1854 The last thing to handle is interlacing; this is covered in detail below,
1855 but you must call the function here if you want libpng to handle expansion
1856 of the interlaced image.
1858 number_of_passes = png_set_interlace_handling(png_ptr);
1860 After setting the transformations, libpng can update your png_info
1861 structure to reflect any transformations you've requested with this
1862 call. This is most useful to update the info structure's rowbytes
1863 field so you can use it to allocate your image memory. This function
1864 will also update your palette with the correct screen_gamma and
1865 background if these have been given with the calls above.
1867 png_read_update_info(png_ptr, info_ptr);
1869 After you call png_read_update_info(), you can allocate any
1870 memory you need to hold the image. The row data is simply
1871 raw byte data for all forms of images. As the actual allocation
1872 varies among applications, no example will be given. If you
1873 are allocating one large chunk, you will need to build an
1874 array of pointers to each row, as it will be needed for some
1875 of the functions below.
1877 .SS Reading image data
1879 After you've allocated memory, you can read the image data.
1880 The simplest way to do this is in one function call. If you are
1881 allocating enough memory to hold the whole image, you can just
1882 call png_read_image() and libpng will read in all the image data
1883 and put it in the memory area supplied. You will need to pass in
1884 an array of pointers to each row.
1886 This function automatically handles interlacing, so you don't need
1887 to call png_set_interlace_handling() or call this function multiple
1888 times, or any of that other stuff necessary with png_read_rows().
1890 png_read_image(png_ptr, row_pointers);
1892 where row_pointers is:
1894 png_bytep row_pointers[height];
1896 You can point to void or char or whatever you use for pixels.
1898 If you don't want to read in the whole image at once, you can
1899 use png_read_rows() instead. If there is no interlacing (check
1900 interlace_type == PNG_INTERLACE_NONE), this is simple:
1902 png_read_rows(png_ptr, row_pointers, NULL,
1905 where row_pointers is the same as in the png_read_image() call.
1907 If you are doing this just one row at a time, you can do this with
1908 a single row_pointer instead of an array of row_pointers:
1910 png_bytep row_pointer = row;
1911 png_read_row(png_ptr, row_pointer, NULL);
1913 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
1914 get somewhat harder. The only current (PNG Specification version 1.2)
1915 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
1916 is a somewhat complicated 2D interlace scheme, known as Adam7, that
1917 breaks down an image into seven smaller images of varying size, based
1920 libpng can fill out those images or it can give them to you "as is".
1921 If you want them filled out, there are two ways to do that. The one
1922 mentioned in the PNG specification is to expand each pixel to cover
1923 those pixels that have not been read yet (the "rectangle" method).
1924 This results in a blocky image for the first pass, which gradually
1925 smooths out as more pixels are read. The other method is the "sparkle"
1926 method, where pixels are drawn only in their final locations, with the
1927 rest of the image remaining whatever colors they were initialized to
1928 before the start of the read. The first method usually looks better,
1929 but tends to be slower, as there are more pixels to put in the rows.
1931 If you don't want libpng to handle the interlacing details, just call
1932 png_read_rows() seven times to read in all seven images. Each of the
1933 images is a valid image by itself, or they can all be combined on an
1934 8x8 grid to form a single image (although if you intend to combine them
1935 you would be far better off using the libpng interlace handling).
1937 The first pass will return an image 1/8 as wide as the entire image
1938 (every 8th column starting in column 0) and 1/8 as high as the original
1939 (every 8th row starting in row 0), the second will be 1/8 as wide
1940 (starting in column 4) and 1/8 as high (also starting in row 0). The
1941 third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
1942 1/8 as high (every 8th row starting in row 4), and the fourth pass will
1943 be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
1944 and every 4th row starting in row 0). The fifth pass will return an
1945 image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
1946 while the sixth pass will be 1/2 as wide and 1/2 as high as the original
1947 (starting in column 1 and row 0). The seventh and final pass will be as
1948 wide as the original, and 1/2 as high, containing all of the odd
1949 numbered scanlines. Phew!
1951 If you want libpng to expand the images, call this before calling
1952 png_start_read_image() or png_read_update_info():
1954 if (interlace_type == PNG_INTERLACE_ADAM7)
1956 = png_set_interlace_handling(png_ptr);
1958 This will return the number of passes needed. Currently, this
1959 is seven, but may change if another interlace type is added.
1960 This function can be called even if the file is not interlaced,
1961 where it will return one pass.
1963 If you are not going to display the image after each pass, but are
1964 going to wait until the entire image is read in, use the sparkle
1965 effect. This effect is faster and the end result of either method
1966 is exactly the same. If you are planning on displaying the image
1967 after each pass, the "rectangle" effect is generally considered the
1970 If you only want the "sparkle" effect, just call png_read_rows() as
1971 normal, with the third parameter NULL. Make sure you make pass over
1972 the image number_of_passes times, and you don't change the data in the
1973 rows between calls. You can change the locations of the data, just
1974 not the data. Each pass only writes the pixels appropriate for that
1975 pass, and assumes the data from previous passes is still valid.
1977 png_read_rows(png_ptr, row_pointers, NULL,
1980 If you only want the first effect (the rectangles), do the same as
1981 before except pass the row buffer in the third parameter, and leave
1982 the second parameter NULL.
1984 png_read_rows(png_ptr, NULL, row_pointers,
1987 .SS Finishing a sequential read
1989 After you are finished reading the image through either the high- or
1990 low-level interfaces, you can finish reading the file. If you are
1991 interested in comments or time, which may be stored either before or
1992 after the image data, you should pass the separate png_info struct if
1993 you want to keep the comments from before and after the image
1994 separate. If you are not interested, you can pass NULL.
1996 png_read_end(png_ptr, end_info);
1998 When you are done, you can free all memory allocated by libpng like this:
2000 png_destroy_read_struct(&png_ptr, &info_ptr,
2003 It is also possible to individually free the info_ptr members that
2004 point to libpng-allocated storage with the following function:
2006 png_free_data(png_ptr, info_ptr, mask, seq)
2007 mask - identifies data to be freed, a mask
2008 containing the logical OR of one or
2010 PNG_FREE_PLTE, PNG_FREE_TRNS,
2011 PNG_FREE_HIST, PNG_FREE_ICCP,
2012 PNG_FREE_PCAL, PNG_FREE_ROWS,
2013 PNG_FREE_SCAL, PNG_FREE_SPLT,
2014 PNG_FREE_TEXT, PNG_FREE_UNKN,
2015 or simply PNG_FREE_ALL
2016 seq - sequence number of item to be freed
2019 This function may be safely called when the relevant storage has
2020 already been freed, or has not yet been allocated, or was allocated
2021 by the user and not by libpng, and will in those
2022 cases do nothing. The "seq" parameter is ignored if only one item
2023 of the selected data type, such as PLTE, is allowed. If "seq" is not
2024 -1, and multiple items are allowed for the data type identified in
2025 the mask, such as text or sPLT, only the n'th item in the structure
2026 is freed, where n is "seq".
2028 The default behavior is only to free data that was allocated internally
2029 by libpng. This can be changed, so that libpng will not free the data,
2030 or so that it will free data that was allocated by the user with png_malloc()
2031 or png_zalloc() and passed in via a png_set_*() function, with
2033 png_data_freer(png_ptr, info_ptr, freer, mask)
2034 mask - which data elements are affected
2035 same choices as in png_free_data()
2037 PNG_DESTROY_WILL_FREE_DATA
2038 PNG_SET_WILL_FREE_DATA
2039 PNG_USER_WILL_FREE_DATA
2041 This function only affects data that has already been allocated.
2042 You can call this function after reading the PNG data but before calling
2043 any png_set_*() functions, to control whether the user or the png_set_*()
2044 function is responsible for freeing any existing data that might be present,
2045 and again after the png_set_*() functions to control whether the user
2046 or png_destroy_*() is supposed to free the data. When the user assumes
2047 responsibility for libpng-allocated data, the application must use
2048 png_free() to free it, and when the user transfers responsibility to libpng
2049 for data that the user has allocated, the user must have used png_malloc()
2050 or png_zalloc() to allocate it.
2052 If you allocated your row_pointers in a single block, as suggested above in
2053 the description of the high level read interface, you must not transfer
2054 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2055 because they would also try to free the individual row_pointers[i].
2057 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2058 separately, do not transfer responsibility for freeing text_ptr to libpng,
2059 because when libpng fills a png_text structure it combines these members with
2060 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2061 if you transfer responsibility for free'ing text_ptr from libpng to your
2062 application, your application must not separately free those members.
2064 The png_free_data() function will turn off the "valid" flag for anything
2065 it frees. If you need to turn the flag off for a chunk that was freed by your
2066 application instead of by libpng, you can use
2068 png_set_invalid(png_ptr, info_ptr, mask);
2069 mask - identifies the chunks to be made invalid,
2070 containing the logical OR of one or
2072 PNG_INFO_gAMA, PNG_INFO_sBIT,
2073 PNG_INFO_cHRM, PNG_INFO_PLTE,
2074 PNG_INFO_tRNS, PNG_INFO_bKGD,
2075 PNG_INFO_hIST, PNG_INFO_pHYs,
2076 PNG_INFO_oFFs, PNG_INFO_tIME,
2077 PNG_INFO_pCAL, PNG_INFO_sRGB,
2078 PNG_INFO_iCCP, PNG_INFO_sPLT,
2079 PNG_INFO_sCAL, PNG_INFO_IDAT
2081 For a more compact example of reading a PNG image, see the file example.c.
2083 .SS Reading PNG files progressively
2085 The progressive reader is slightly different then the non-progressive
2086 reader. Instead of calling png_read_info(), png_read_rows(), and
2087 png_read_end(), you make one call to png_process_data(), which calls
2088 callbacks when it has the info, a row, or the end of the image. You
2089 set up these callbacks with png_set_progressive_read_fn(). You don't
2090 have to worry about the input/output functions of libpng, as you are
2091 giving the library the data directly in png_process_data(). I will
2092 assume that you have read the section on reading PNG files above,
2093 so I will only highlight the differences (although I will show
2096 png_structp png_ptr;
2099 /* An example code fragment of how you would
2100 initialize the progressive reader in your
2103 initialize_png_reader()
2105 png_ptr = png_create_read_struct
2106 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2107 user_error_fn, user_warning_fn);
2110 info_ptr = png_create_info_struct(png_ptr);
2113 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2118 if (setjmp(png_jmpbuf(png_ptr)))
2120 png_destroy_read_struct(&png_ptr, &info_ptr,
2125 /* This one's new. You can provide functions
2126 to be called when the header info is valid,
2127 when each row is completed, and when the image
2128 is finished. If you aren't using all functions,
2129 you can specify NULL parameters. Even when all
2130 three functions are NULL, you need to call
2131 png_set_progressive_read_fn(). You can use
2132 any struct as the user_ptr (cast to a void pointer
2133 for the function call), and retrieve the pointer
2134 from inside the callbacks using the function
2136 png_get_progressive_ptr(png_ptr);
2138 which will return a void pointer, which you have
2139 to cast appropriately.
2141 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2142 info_callback, row_callback, end_callback);
2147 /* A code fragment that you call as you receive blocks
2150 process_data(png_bytep buffer, png_uint_32 length)
2152 if (setjmp(png_jmpbuf(png_ptr)))
2154 png_destroy_read_struct(&png_ptr, &info_ptr,
2159 /* This one's new also. Simply give it a chunk
2160 of data from the file stream (in order, of
2161 course). On machines with segmented memory
2162 models machines, don't give it any more than
2163 64K. The library seems to run fine with sizes
2164 of 4K. Although you can give it much less if
2165 necessary (I assume you can give it chunks of
2166 1 byte, I haven't tried less then 256 bytes
2167 yet). When this function returns, you may
2168 want to display any rows that were generated
2169 in the row callback if you don't already do
2172 png_process_data(png_ptr, info_ptr, buffer, length);
2176 /* This function is called (as set by
2177 png_set_progressive_read_fn() above) when enough data
2178 has been supplied so all of the header has been
2182 info_callback(png_structp png_ptr, png_infop info)
2184 /* Do any setup here, including setting any of
2185 the transformations mentioned in the Reading
2186 PNG files section. For now, you _must_ call
2187 either png_start_read_image() or
2188 png_read_update_info() after all the
2189 transformations are set (even if you don't set
2190 any). You may start getting rows before
2191 png_process_data() returns, so this is your
2192 last chance to prepare for that.
2196 /* This function is called when each row of image
2199 row_callback(png_structp png_ptr, png_bytep new_row,
2200 png_uint_32 row_num, int pass)
2202 /* If the image is interlaced, and you turned
2203 on the interlace handler, this function will
2204 be called for every row in every pass. Some
2205 of these rows will not be changed from the
2206 previous pass. When the row is not changed,
2207 the new_row variable will be NULL. The rows
2208 and passes are called in order, so you don't
2209 really need the row_num and pass, but I'm
2210 supplying them because it may make your life
2213 For the non-NULL rows of interlaced images,
2214 you must call png_progressive_combine_row()
2215 passing in the row and the old row. You can
2216 call this function for NULL rows (it will just
2217 return) and for non-interlaced images (it just
2218 does the memcpy for you) if it will make the
2219 code easier. Thus, you can just do this for
2223 png_progressive_combine_row(png_ptr, old_row,
2226 /* where old_row is what was displayed for
2227 previously for the row. Note that the first
2228 pass (pass == 0, really) will completely cover
2229 the old row, so the rows do not have to be
2230 initialized. After the first pass (and only
2231 for interlaced images), you will have to pass
2232 the current row, and the function will combine
2233 the old row and the new row.
2238 end_callback(png_structp png_ptr, png_infop info)
2240 /* This function is called after the whole image
2241 has been read, including any chunks after the
2242 image (up to and including the IEND). You
2243 will usually have the same info chunk as you
2244 had in the header, although some data may have
2245 been added to the comments and time fields.
2247 Most people won't do much here, perhaps setting
2248 a flag that marks the image as finished.
2256 Much of this is very similar to reading. However, everything of
2257 importance is repeated here, so you won't have to constantly look
2258 back up in the reading section to understand writing.
2262 You will want to do the I/O initialization before you get into libpng,
2263 so if it doesn't work, you don't have anything to undo. If you are not
2264 using the standard I/O functions, you will need to replace them with
2265 custom writing functions. See the discussion under Customizing libpng.
2267 FILE *fp = fopen(file_name, "wb");
2273 Next, png_struct and png_info need to be allocated and initialized.
2274 As these can be both relatively large, you may not want to store these
2275 on the stack, unless you have stack space to spare. Of course, you
2276 will want to check if they return NULL. If you are also reading,
2277 you won't want to name your read structure and your write structure
2278 both "png_ptr"; you can call them anything you like, such as
2279 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
2281 png_structp png_ptr = png_create_write_struct
2282 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2283 user_error_fn, user_warning_fn);
2287 png_infop info_ptr = png_create_info_struct(png_ptr);
2290 png_destroy_write_struct(&png_ptr,
2295 If you want to use your own memory allocation routines,
2296 define PNG_USER_MEM_SUPPORTED and use
2297 png_create_write_struct_2() instead of png_create_write_struct():
2299 png_structp png_ptr = png_create_write_struct_2
2300 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2301 user_error_fn, user_warning_fn, (png_voidp)
2302 user_mem_ptr, user_malloc_fn, user_free_fn);
2304 After you have these structures, you will need to set up the
2305 error handling. When libpng encounters an error, it expects to
2306 longjmp() back to your routine. Therefore, you will need to call
2307 setjmp() and pass the png_jmpbuf(png_ptr). If you
2308 write the file from different routines, you will need to update
2309 the png_jmpbuf(png_ptr) every time you enter a new routine that will
2310 call a png_*() function. See your documentation of setjmp/longjmp
2311 for your compiler for more information on setjmp/longjmp. See
2312 the discussion on libpng error handling in the Customizing Libpng
2313 section below for more information on the libpng error handling.
2315 if (setjmp(png_jmpbuf(png_ptr)))
2317 png_destroy_write_struct(&png_ptr, &info_ptr);
2324 If you would rather avoid the complexity of setjmp/longjmp issues,
2325 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2326 errors will result in a call to PNG_ABORT() which defaults to abort().
2328 Now you need to set up the output code. The default for libpng is to
2329 use the C function fwrite(). If you use this, you will need to pass a
2330 valid FILE * in the function png_init_io(). Be sure that the file is
2331 opened in binary mode. Again, if you wish to handle writing data in
2332 another way, see the discussion on libpng I/O handling in the Customizing
2333 Libpng section below.
2335 png_init_io(png_ptr, fp);
2339 At this point, you can set up a callback function that will be
2340 called after each row has been written, which you can use to control
2341 a progress meter or the like. It's demonstrated in pngtest.c.
2342 You must supply a function
2344 void write_row_callback(png_ptr, png_uint_32 row,
2347 /* put your code here */
2350 (You can give it another name that you like instead of "write_row_callback")
2352 To inform libpng about your function, use
2354 png_set_write_status_fn(png_ptr, write_row_callback);
2356 You now have the option of modifying how the compression library will
2357 run. The following functions are mainly for testing, but may be useful
2358 in some cases, like if you need to write PNG files extremely fast and
2359 are willing to give up some compression, or if you want to get the
2360 maximum possible compression at the expense of slower writing. If you
2361 have no special needs in this area, let the library do what it wants by
2362 not calling this function at all, as it has been tuned to deliver a good
2363 speed/compression ratio. The second parameter to png_set_filter() is
2364 the filter method, for which the only valid values are 0 (as of the
2365 July 1999 PNG specification, version 1.2) or 64 (if you are writing
2366 a PNG datastream that is to be embedded in a MNG datastream). The third
2367 parameter is a flag that indicates which filter type(s) are to be tested
2368 for each scanline. See the PNG specification for details on the specific filter
2372 /* turn on or off filtering, and/or choose
2373 specific filters. You can use either a single
2374 PNG_FILTER_VALUE_NAME or the logical OR of one
2375 or more PNG_FILTER_NAME masks. */
2376 png_set_filter(png_ptr, 0,
2377 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2378 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2379 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2380 PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2381 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2385 wants to start and stop using particular filters during compression,
2386 it should start out with all of the filters (to ensure that the previous
2387 row of pixels will be stored in case it's needed later), and then add
2388 and remove them after the start of compression.
2390 If you are writing a PNG datastream that is to be embedded in a MNG
2391 datastream, the second parameter can be either 0 or 64.
2393 The png_set_compression_*() functions interface to the zlib compression
2394 library, and should mostly be ignored unless you really know what you are
2395 doing. The only generally useful call is png_set_compression_level()
2396 which changes how much time zlib spends on trying to compress the image
2397 data. See the Compression Library (zlib.h and algorithm.txt, distributed
2398 with zlib) for details on the compression levels.
2400 /* set the zlib compression level */
2401 png_set_compression_level(png_ptr,
2402 Z_BEST_COMPRESSION);
2404 /* set other zlib parameters */
2405 png_set_compression_mem_level(png_ptr, 8);
2406 png_set_compression_strategy(png_ptr,
2407 Z_DEFAULT_STRATEGY);
2408 png_set_compression_window_bits(png_ptr, 15);
2409 png_set_compression_method(png_ptr, 8);
2410 png_set_compression_buffer_size(png_ptr, 8192)
2412 extern PNG_EXPORT(void,png_set_zbuf_size)
2414 .SS Setting the contents of info for output
2416 You now need to fill in the png_info structure with all the data you
2417 wish to write before the actual image. Note that the only thing you
2418 are allowed to write after the image is the text chunks and the time
2419 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2420 the latest PNG specification for more information on that. If you
2421 wish to write them before the image, fill them in now, and flag that
2422 data as being valid. If you want to wait until after the data, don't
2423 fill them until png_write_end(). For all the fields in png_info and
2424 their data types, see png.h. For explanations of what the fields
2425 contain, see the PNG specification.
2427 Some of the more important parts of the png_info are:
2429 png_set_IHDR(png_ptr, info_ptr, width, height,
2430 bit_depth, color_type, interlace_type,
2431 compression_type, filter_method)
2432 width - holds the width of the image
2433 in pixels (up to 2^31).
2434 height - holds the height of the image
2435 in pixels (up to 2^31).
2436 bit_depth - holds the bit depth of one of the
2438 (valid values are 1, 2, 4, 8, 16
2439 and depend also on the
2440 color_type. See also significant
2442 color_type - describes which color/alpha
2443 channels are present.
2445 (bit depths 1, 2, 4, 8, 16)
2446 PNG_COLOR_TYPE_GRAY_ALPHA
2448 PNG_COLOR_TYPE_PALETTE
2449 (bit depths 1, 2, 4, 8)
2452 PNG_COLOR_TYPE_RGB_ALPHA
2455 PNG_COLOR_MASK_PALETTE
2456 PNG_COLOR_MASK_COLOR
2457 PNG_COLOR_MASK_ALPHA
2459 interlace_type - PNG_INTERLACE_NONE or
2461 compression_type - (must be
2462 PNG_COMPRESSION_TYPE_DEFAULT)
2463 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2464 or, if you are writing a PNG to
2465 be embedded in a MNG datastream,
2467 PNG_INTRAPIXEL_DIFFERENCING)
2469 png_set_PLTE(png_ptr, info_ptr, palette,
2471 palette - the palette for the file
2472 (array of png_color)
2473 num_palette - number of entries in the palette
2475 png_set_gAMA(png_ptr, info_ptr, gamma);
2476 gamma - the gamma the image was created
2479 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2480 srgb_intent - the rendering intent
2481 (PNG_INFO_sRGB) The presence of
2482 the sRGB chunk means that the pixel
2483 data is in the sRGB color space.
2484 This chunk also implies specific
2485 values of gAMA and cHRM. Rendering
2486 intent is the CSS-1 property that
2487 has been defined by the International
2489 (http://www.color.org).
2491 PNG_sRGB_INTENT_SATURATION,
2492 PNG_sRGB_INTENT_PERCEPTUAL,
2493 PNG_sRGB_INTENT_ABSOLUTE, or
2494 PNG_sRGB_INTENT_RELATIVE.
2497 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2499 srgb_intent - the rendering intent
2500 (PNG_INFO_sRGB) The presence of the
2501 sRGB chunk means that the pixel
2502 data is in the sRGB color space.
2503 This function also causes gAMA and
2504 cHRM chunks with the specific values
2505 that are consistent with sRGB to be
2508 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2510 name - The profile name.
2511 compression - The compression type; always
2512 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2513 You may give NULL to this argument to
2515 profile - International Color Consortium color
2516 profile data. May contain NULs.
2517 proflen - length of profile data in bytes.
2519 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2520 sig_bit - the number of significant bits for
2521 (PNG_INFO_sBIT) each of the gray, red,
2522 green, and blue channels, whichever are
2523 appropriate for the given color type
2526 png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2528 trans - array of transparent entries for
2529 palette (PNG_INFO_tRNS)
2530 trans_values - graylevel or color sample values of
2531 the single transparent color for
2532 non-paletted images (PNG_INFO_tRNS)
2533 num_trans - number of transparent entries
2536 png_set_hIST(png_ptr, info_ptr, hist);
2538 hist - histogram of palette (array of
2541 png_set_tIME(png_ptr, info_ptr, mod_time);
2542 mod_time - time image was last modified
2545 png_set_bKGD(png_ptr, info_ptr, background);
2546 background - background color (PNG_VALID_bKGD)
2548 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2549 text_ptr - array of png_text holding image
2551 text_ptr[i].compression - type of compression used
2552 on "text" PNG_TEXT_COMPRESSION_NONE
2553 PNG_TEXT_COMPRESSION_zTXt
2554 PNG_ITXT_COMPRESSION_NONE
2555 PNG_ITXT_COMPRESSION_zTXt
2556 text_ptr[i].key - keyword for comment. Must contain
2558 text_ptr[i].text - text comments for current
2559 keyword. Can be NULL or empty.
2560 text_ptr[i].text_length - length of text string,
2561 after decompression, 0 for iTXt
2562 text_ptr[i].itxt_length - length of itxt string,
2563 after decompression, 0 for tEXt/zTXt
2564 text_ptr[i].lang - language of comment (NULL or
2566 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2567 or empty for unknown).
2568 num_text - number of comments
2570 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2572 palette_ptr - array of png_sPLT_struct structures
2573 to be added to the list of palettes
2574 in the info structure.
2575 num_spalettes - number of palette structures to be
2578 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2580 offset_x - positive offset from the left
2582 offset_y - positive offset from the top
2584 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2586 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2588 res_x - pixels/unit physical resolution
2590 res_y - pixels/unit physical resolution
2592 unit_type - PNG_RESOLUTION_UNKNOWN,
2593 PNG_RESOLUTION_METER
2595 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2596 unit - physical scale units (an integer)
2597 width - width of a pixel in physical scale units
2598 height - height of a pixel in physical scale units
2599 (width and height are doubles)
2601 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2602 unit - physical scale units (an integer)
2603 width - width of a pixel in physical scale units
2604 height - height of a pixel in physical scale units
2605 (width and height are strings like "2.54")
2607 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2609 unknowns - array of png_unknown_chunk
2610 structures holding unknown chunks
2611 unknowns[i].name - name of unknown chunk
2612 unknowns[i].data - data of unknown chunk
2613 unknowns[i].size - size of unknown chunk's data
2614 unknowns[i].location - position to write chunk in file
2615 0: do not write chunk
2616 PNG_HAVE_IHDR: before PLTE
2617 PNG_HAVE_PLTE: before IDAT
2618 PNG_AFTER_IDAT: after IDAT
2620 The "location" member is set automatically according to
2621 what part of the output file has already been written.
2622 You can change its value after calling png_set_unknown_chunks()
2623 as demonstrated in pngtest.c. Within each of the "locations",
2624 the chunks are sequenced according to their position in the
2625 structure (that is, the value of "i", which is the order in which
2626 the chunk was either read from the input file or defined with
2627 png_set_unknown_chunks).
2629 A quick word about text and num_text. text is an array of png_text
2630 structures. num_text is the number of valid structures in the array.
2631 Each png_text structure holds a language code, a keyword, a text value,
2632 and a compression type.
2634 The compression types have the same valid numbers as the compression
2635 types of the image data. Currently, the only valid number is zero.
2636 However, you can store text either compressed or uncompressed, unlike
2637 images, which always have to be compressed. So if you don't want the
2638 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2639 Because tEXt and zTXt chunks don't have a language field, if you
2640 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2641 any language code or translated keyword will not be written out.
2643 Until text gets around 1000 bytes, it is not worth compressing it.
2644 After the text has been written out to the file, the compression type
2645 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2646 so that it isn't written out again at the end (in case you are calling
2647 png_write_end() with the same struct.
2649 The keywords that are given in the PNG Specification are:
2651 Title Short (one line) title or
2653 Author Name of image's creator
2654 Description Description of image (possibly long)
2655 Copyright Copyright notice
2656 Creation Time Time of original image creation
2657 (usually RFC 1123 format, see below)
2658 Software Software used to create the image
2659 Disclaimer Legal disclaimer
2660 Warning Warning of nature of content
2661 Source Device used to create the image
2662 Comment Miscellaneous comment; conversion
2663 from other image format
2665 The keyword-text pairs work like this. Keywords should be short
2666 simple descriptions of what the comment is about. Some typical
2667 keywords are found in the PNG specification, as is some recommendations
2668 on keywords. You can repeat keywords in a file. You can even write
2669 some text before the image and some after. For example, you may want
2670 to put a description of the image before the image, but leave the
2671 disclaimer until after, so viewers working over modem connections
2672 don't have to wait for the disclaimer to go over the modem before
2673 they start seeing the image. Finally, keywords should be full
2674 words, not abbreviations. Keywords and text are in the ISO 8859-1
2675 (Latin-1) character set (a superset of regular ASCII) and can not
2676 contain NUL characters, and should not contain control or other
2677 unprintable characters. To make the comments widely readable, stick
2678 with basic ASCII, and avoid machine specific character set extensions
2679 like the IBM-PC character set. The keyword must be present, but
2680 you can leave off the text string on non-compressed pairs.
2681 Compressed pairs must have a text string, as only the text string
2682 is compressed anyway, so the compression would be meaningless.
2684 PNG supports modification time via the png_time structure. Two
2685 conversion routines are provided, png_convert_from_time_t() for
2686 time_t and png_convert_from_struct_tm() for struct tm. The
2687 time_t routine uses gmtime(). You don't have to use either of
2688 these, but if you wish to fill in the png_time structure directly,
2689 you should provide the time in universal time (GMT) if possible
2690 instead of your local time. Note that the year number is the full
2691 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2692 that months start with 1.
2694 If you want to store the time of the original image creation, you should
2695 use a plain tEXt chunk with the "Creation Time" keyword. This is
2696 necessary because the "creation time" of a PNG image is somewhat vague,
2697 depending on whether you mean the PNG file, the time the image was
2698 created in a non-PNG format, a still photo from which the image was
2699 scanned, or possibly the subject matter itself. In order to facilitate
2700 machine-readable dates, it is recommended that the "Creation Time"
2701 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2702 although this isn't a requirement. Unlike the tIME chunk, the
2703 "Creation Time" tEXt chunk is not expected to be automatically changed
2704 by the software. To facilitate the use of RFC 1123 dates, a function
2705 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2706 time to an RFC 1123 format string.
2708 .SS Writing unknown chunks
2710 You can use the png_set_unknown_chunks function to queue up chunks
2711 for writing. You give it a chunk name, raw data, and a size; that's
2712 all there is to it. The chunks will be written by the next following
2713 png_write_info_before_PLTE, png_write_info, or png_write_end function.
2714 Any chunks previously read into the info structure's unknown-chunk
2715 list will also be written out in a sequence that satisfies the PNG
2716 specification's ordering rules.
2718 .SS The high-level write interface
2720 At this point there are two ways to proceed; through the high-level
2721 write interface, or through a sequence of low-level write operations.
2722 You can use the high-level interface if your image data is present
2723 in the info structure. All defined output
2724 transformations are permitted, enabled by the following masks.
2726 PNG_TRANSFORM_IDENTITY No transformation
2727 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2728 PNG_TRANSFORM_PACKSWAP Change order of packed
2730 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2731 PNG_TRANSFORM_SHIFT Normalize pixels to the
2733 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2735 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2737 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2739 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2740 PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2742 If you have valid image data in the info structure (you can use
2743 png_set_rows() to put image data in the info structure), simply do this:
2745 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2747 where png_transforms is an integer containing the logical OR of some set of
2748 transformation flags. This call is equivalent to png_write_info(),
2749 followed the set of transformations indicated by the transform mask,
2750 then png_write_image(), and finally png_write_end().
2752 (The final parameter of this call is not yet used. Someday it might point
2753 to transformation parameters required by some future output transform.)
2755 .SS The low-level write interface
2757 If you are going the low-level route instead, you are now ready to
2758 write all the file information up to the actual image data. You do
2759 this with a call to png_write_info().
2761 png_write_info(png_ptr, info_ptr);
2763 Note that there is one transformation you may need to do before
2764 png_write_info(). In PNG files, the alpha channel in an image is the
2765 level of opacity. If your data is supplied as a level of
2766 transparency, you can invert the alpha channel before you write it, so
2767 that 0 is fully transparent and 255 (in 8-bit or paletted images) or
2768 65535 (in 16-bit images) is fully opaque, with
2770 png_set_invert_alpha(png_ptr);
2772 This must appear before png_write_info() instead of later with the
2773 other transformations because in the case of paletted images the tRNS
2774 chunk data has to be inverted before the tRNS chunk is written. If
2775 your image is not a paletted image, the tRNS data (which in such cases
2776 represents a single color to be rendered as transparent) won't need to
2777 be changed, and you can safely do this transformation after your
2778 png_write_info() call.
2780 If you need to write a private chunk that you want to appear before
2781 the PLTE chunk when PLTE is present, you can write the PNG info in
2782 two steps, and insert code to write your own chunk between them:
2784 png_write_info_before_PLTE(png_ptr, info_ptr);
2785 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2786 png_write_info(png_ptr, info_ptr);
2788 After you've written the file information, you can set up the library
2789 to handle any special transformations of the image data. The various
2790 ways to transform the data will be described in the order that they
2791 should occur. This is important, as some of these change the color
2792 type and/or bit depth of the data, and some others only work on
2793 certain color types and bit depths. Even though each transformation
2794 checks to see if it has data that it can do something with, you should
2795 make sure to only enable a transformation if it will be valid for the
2796 data. For example, don't swap red and blue on grayscale data.
2798 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2799 the library to strip input data that has 4 or 8 bytes per pixel down
2800 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2803 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2805 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2806 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2807 is stored XRGB or RGBX.
2809 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2810 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2811 If the data is supplied at 1 pixel per byte, use this code, which will
2812 correctly pack the pixels into a single byte:
2814 png_set_packing(png_ptr);
2816 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2817 data is of another bit depth, you can write an sBIT chunk into the
2818 file so that decoders can recover the original data if desired.
2820 /* Set the true bit depth of the image data */
2821 if (color_type & PNG_COLOR_MASK_COLOR)
2823 sig_bit.red = true_bit_depth;
2824 sig_bit.green = true_bit_depth;
2825 sig_bit.blue = true_bit_depth;
2829 sig_bit.gray = true_bit_depth;
2831 if (color_type & PNG_COLOR_MASK_ALPHA)
2833 sig_bit.alpha = true_bit_depth;
2836 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2838 If the data is stored in the row buffer in a bit depth other than
2839 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2840 this will scale the values to appear to be the correct bit depth as
2843 png_set_shift(png_ptr, &sig_bit);
2845 PNG files store 16 bit pixels in network byte order (big-endian,
2846 ie. most significant bits first). This code would be used if they are
2847 supplied the other way (little-endian, i.e. least significant bits
2848 first, the way PCs store them):
2851 png_set_swap(png_ptr);
2853 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2854 need to change the order the pixels are packed into bytes, you can use:
2857 png_set_packswap(png_ptr);
2859 PNG files store 3 color pixels in red, green, blue order. This code
2860 would be used if they are supplied as blue, green, red:
2862 png_set_bgr(png_ptr);
2864 PNG files describe monochrome as black being zero and white being
2865 one. This code would be used if the pixels are supplied with this reversed
2866 (black being one and white being zero):
2868 png_set_invert_mono(png_ptr);
2870 Finally, you can write your own transformation function if none of
2871 the existing ones meets your needs. This is done by setting a callback
2874 png_set_write_user_transform_fn(png_ptr,
2875 write_transform_fn);
2877 You must supply the function
2879 void write_transform_fn(png_ptr ptr, row_info_ptr
2880 row_info, png_bytep data)
2882 See pngtest.c for a working example. Your function will be called
2883 before any of the other transformations are processed.
2885 You can also set up a pointer to a user structure for use by your
2888 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
2890 The user_channels and user_depth parameters of this function are ignored
2891 when writing; you can set them to zero as shown.
2893 You can retrieve the pointer via the function png_get_user_transform_ptr().
2896 voidp write_user_transform_ptr =
2897 png_get_user_transform_ptr(png_ptr);
2899 It is possible to have libpng flush any pending output, either manually,
2900 or automatically after a certain number of lines have been written. To
2901 flush the output stream a single time call:
2903 png_write_flush(png_ptr);
2905 and to have libpng flush the output stream periodically after a certain
2906 number of scanlines have been written, call:
2908 png_set_flush(png_ptr, nrows);
2910 Note that the distance between rows is from the last time png_write_flush()
2911 was called, or the first row of the image if it has never been called.
2912 So if you write 50 lines, and then png_set_flush 25, it will flush the
2913 output on the next scanline, and every 25 lines thereafter, unless
2914 png_write_flush() is called before 25 more lines have been written.
2915 If nrows is too small (less than about 10 lines for a 640 pixel wide
2916 RGB image) the image compression may decrease noticeably (although this
2917 may be acceptable for real-time applications). Infrequent flushing will
2918 only degrade the compression performance by a few percent over images
2919 that do not use flushing.
2921 .SS Writing the image data
2923 That's it for the transformations. Now you can write the image data.
2924 The simplest way to do this is in one function call. If you have the
2925 whole image in memory, you can just call png_write_image() and libpng
2926 will write the image. You will need to pass in an array of pointers to
2927 each row. This function automatically handles interlacing, so you don't
2928 need to call png_set_interlace_handling() or call this function multiple
2929 times, or any of that other stuff necessary with png_write_rows().
2931 png_write_image(png_ptr, row_pointers);
2933 where row_pointers is:
2935 png_byte *row_pointers[height];
2937 You can point to void or char or whatever you use for pixels.
2939 If you don't want to write the whole image at once, you can
2940 use png_write_rows() instead. If the file is not interlaced,
2943 png_write_rows(png_ptr, row_pointers,
2946 row_pointers is the same as in the png_write_image() call.
2948 If you are just writing one row at a time, you can do this with
2949 a single row_pointer instead of an array of row_pointers:
2951 png_bytep row_pointer = row;
2953 png_write_row(png_ptr, row_pointer);
2955 When the file is interlaced, things can get a good deal more
2956 complicated. The only currently (as of the PNG Specification
2957 version 1.2, dated July 1999) defined interlacing scheme for PNG files
2958 is the "Adam7" interlace scheme, that breaks down an
2959 image into seven smaller images of varying size. libpng will build
2960 these images for you, or you can do them yourself. If you want to
2961 build them yourself, see the PNG specification for details of which
2962 pixels to write when.
2964 If you don't want libpng to handle the interlacing details, just
2965 use png_set_interlace_handling() and call png_write_rows() the
2966 correct number of times to write all seven sub-images.
2968 If you want libpng to build the sub-images, call this before you start
2972 png_set_interlace_handling(png_ptr);
2974 This will return the number of passes needed. Currently, this
2975 is seven, but may change if another interlace type is added.
2977 Then write the complete image number_of_passes times.
2979 png_write_rows(png_ptr, row_pointers,
2982 As some of these rows are not used, and thus return immediately,
2983 you may want to read about interlacing in the PNG specification,
2984 and only update the rows that are actually used.
2986 .SS Finishing a sequential write
2988 After you are finished writing the image, you should finish writing
2989 the file. If you are interested in writing comments or time, you should
2990 pass an appropriately filled png_info pointer. If you are not interested,
2993 png_write_end(png_ptr, info_ptr);
2995 When you are done, you can free all memory used by libpng like this:
2997 png_destroy_write_struct(&png_ptr, &info_ptr);
2999 It is also possible to individually free the info_ptr members that
3000 point to libpng-allocated storage with the following function:
3002 png_free_data(png_ptr, info_ptr, mask, seq)
3003 mask - identifies data to be freed, a mask
3004 containing the logical OR of one or
3006 PNG_FREE_PLTE, PNG_FREE_TRNS,
3007 PNG_FREE_HIST, PNG_FREE_ICCP,
3008 PNG_FREE_PCAL, PNG_FREE_ROWS,
3009 PNG_FREE_SCAL, PNG_FREE_SPLT,
3010 PNG_FREE_TEXT, PNG_FREE_UNKN,
3011 or simply PNG_FREE_ALL
3012 seq - sequence number of item to be freed
3015 This function may be safely called when the relevant storage has
3016 already been freed, or has not yet been allocated, or was allocated
3017 by the user and not by libpng, and will in those
3018 cases do nothing. The "seq" parameter is ignored if only one item
3019 of the selected data type, such as PLTE, is allowed. If "seq" is not
3020 -1, and multiple items are allowed for the data type identified in
3021 the mask, such as text or sPLT, only the n'th item in the structure
3022 is freed, where n is "seq".
3024 If you allocated data such as a palette that you passed
3025 in to libpng with png_set_*, you must not free it until just before the call to
3026 png_destroy_write_struct().
3028 The default behavior is only to free data that was allocated internally
3029 by libpng. This can be changed, so that libpng will not free the data,
3030 or so that it will free data that was allocated by the user with png_malloc()
3031 or png_zalloc() and passed in via a png_set_*() function, with
3033 png_data_freer(png_ptr, info_ptr, freer, mask)
3034 mask - which data elements are affected
3035 same choices as in png_free_data()
3037 PNG_DESTROY_WILL_FREE_DATA
3038 PNG_SET_WILL_FREE_DATA
3039 PNG_USER_WILL_FREE_DATA
3041 For example, to transfer responsibility for some data from a read structure
3042 to a write structure, you could use
3044 png_data_freer(read_ptr, read_info_ptr,
3045 PNG_USER_WILL_FREE_DATA,
3046 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3047 png_data_freer(write_ptr, write_info_ptr,
3048 PNG_DESTROY_WILL_FREE_DATA,
3049 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3051 thereby briefly reassigning responsibility for freeing to the user but
3052 immediately afterwards reassigning it once more to the write_destroy
3053 function. Having done this, it would then be safe to destroy the read
3054 structure and continue to use the PLTE, tRNS, and hIST data in the write
3057 This function only affects data that has already been allocated.
3058 You can call this function before calling after the png_set_*() functions
3059 to control whether the user or png_destroy_*() is supposed to free the data.
3060 When the user assumes responsibility for libpng-allocated data, the
3061 application must use
3062 png_free() to free it, and when the user transfers responsibility to libpng
3063 for data that the user has allocated, the user must have used png_malloc()
3064 or png_zalloc() to allocate it.
3066 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3067 separately, do not transfer responsibility for freeing text_ptr to libpng,
3068 because when libpng fills a png_text structure it combines these members with
3069 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3070 if you transfer responsibility for free'ing text_ptr from libpng to your
3071 application, your application must not separately free those members.
3072 For a more compact example of writing a PNG image, see the file example.c.
3074 .SH V. Modifying/Customizing libpng:
3076 There are three issues here. The first is changing how libpng does
3077 standard things like memory allocation, input/output, and error handling.
3078 The second deals with more complicated things like adding new chunks,
3079 adding new transformations, and generally changing how libpng works.
3080 Both of those are compile-time issues; that is, they are generally
3081 determined at the time the code is written, and there is rarely a need
3082 to provide the user with a means of changing them. The third is a
3083 run-time issue: choosing between and/or tuning one or more alternate
3084 versions of computationally intensive routines; specifically, optimized
3085 assembly-language (and therefore compiler- and platform-dependent)
3088 Memory allocation, input/output, and error handling
3090 All of the memory allocation, input/output, and error handling in libpng
3091 goes through callbacks that are user-settable. The default routines are
3092 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3093 these functions, call the appropriate png_set_*_fn() function.
3095 Memory allocation is done through the functions png_malloc()
3096 and png_free(). These currently just call the standard C functions. If
3097 your pointers can't access more then 64K at a time, you will want to set
3098 MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
3099 memory allocation on a platform will change between applications, these
3100 functions must be modified in the library at compile time. If you prefer
3101 to use a different method of allocating and freeing data, you can use
3102 png_create_read_struct_2() or png_create_write_struct_2() to register
3103 your own functions as described above.
3105 These functions also provide a void pointer that can be retrieved via
3107 mem_ptr=png_get_mem_ptr(png_ptr);
3109 Your replacement memory functions must have prototypes as follows:
3111 png_voidp malloc_fn(png_structp png_ptr,
3113 void free_fn(png_structp png_ptr, png_voidp ptr);
3115 Your malloc_fn() should return NULL in case of failure. The png_malloc()
3116 function will call png_error() if it receives a NULL from the system
3117 memory allocator or from your replacement malloc_fn().
3119 Input/Output in libpng is done through png_read() and png_write(),
3120 which currently just call fread() and fwrite(). The FILE * is stored in
3121 png_struct and is initialized via png_init_io(). If you wish to change
3122 the method of I/O, the library supplies callbacks that you can set
3123 through the function png_set_read_fn() and png_set_write_fn() at run
3124 time, instead of calling the png_init_io() function. These functions
3125 also provide a void pointer that can be retrieved via the function
3126 png_get_io_ptr(). For example:
3128 png_set_read_fn(png_structp read_ptr,
3129 voidp read_io_ptr, png_rw_ptr read_data_fn)
3131 png_set_write_fn(png_structp write_ptr,
3132 voidp write_io_ptr, png_rw_ptr write_data_fn,
3133 png_flush_ptr output_flush_fn);
3135 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3136 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3138 The replacement I/O functions must have prototypes as follows:
3140 void user_read_data(png_structp png_ptr,
3141 png_bytep data, png_size_t length);
3142 void user_write_data(png_structp png_ptr,
3143 png_bytep data, png_size_t length);
3144 void user_flush_data(png_structp png_ptr);
3146 Supplying NULL for the read, write, or flush functions sets them back
3147 to using the default C stream functions. It is an error to read from
3148 a write stream, and vice versa.
3150 Error handling in libpng is done through png_error() and png_warning().
3151 Errors handled through png_error() are fatal, meaning that png_error()
3152 should never return to its caller. Currently, this is handled via
3153 setjmp() and longjmp() (unless you have compiled libpng with
3154 PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3155 but you could change this to do things like exit() if you should wish.
3157 On non-fatal errors, png_warning() is called
3158 to print a warning message, and then control returns to the calling code.
3159 By default png_error() and png_warning() print a message on stderr via
3160 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3161 (because you don't want the messages) or PNG_NO_STDIO defined (because
3162 fprintf() isn't available). If you wish to change the behavior of the error
3163 functions, you will need to set up your own message callbacks. These
3164 functions are normally supplied at the time that the png_struct is created.
3165 It is also possible to redirect errors and warnings to your own replacement
3166 functions after png_create_*_struct() has been called by calling:
3168 png_set_error_fn(png_structp png_ptr,
3169 png_voidp error_ptr, png_error_ptr error_fn,
3170 png_error_ptr warning_fn);
3172 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3174 If NULL is supplied for either error_fn or warning_fn, then the libpng
3175 default function will be used, calling fprintf() and/or longjmp() if a
3176 problem is encountered. The replacement error functions should have
3177 parameters as follows:
3179 void user_error_fn(png_structp png_ptr,
3180 png_const_charp error_msg);
3181 void user_warning_fn(png_structp png_ptr,
3182 png_const_charp warning_msg);
3184 The motivation behind using setjmp() and longjmp() is the C++ throw and
3185 catch exception handling methods. This makes the code much easier to write,
3186 as there is no need to check every return code of every function call.
3187 However, there are some uncertainties about the status of local variables
3188 after a longjmp, so the user may want to be careful about doing anything after
3189 setjmp returns non-zero besides returning itself. Consult your compiler
3190 documentation for more details. For an alternative approach, you may wish
3191 to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3195 If you need to read or write custom chunks, you may need to get deeper
3196 into the libpng code. The library now has mechanisms for storing
3197 and writing chunks of unknown type; you can even declare callbacks
3198 for custom chunks. Hoewver, this may not be good enough if the
3199 library code itself needs to know about interactions between your
3200 chunk and existing `intrinsic' chunks.
3202 If you need to write a new intrinsic chunk, first read the PNG
3203 specification. Acquire a first level of
3204 understanding of how it works. Pay particular attention to the
3205 sections that describe chunk names, and look at how other chunks were
3206 designed, so you can do things similarly. Second, check out the
3207 sections of libpng that read and write chunks. Try to find a chunk
3208 that is similar to yours and use it as a template. More details can
3209 be found in the comments inside the code. It is best to handle unknown
3210 chunks in a generic method, via callback functions, instead of by
3211 modifying libpng functions.
3213 If you wish to write your own transformation for the data, look through
3214 the part of the code that does the transformations, and check out some of
3215 the simpler ones to get an idea of how they work. Try to find a similar
3216 transformation to the one you want to add and copy off of it. More details
3217 can be found in the comments inside the code itself.
3219 .SS Configuring for 16 bit platforms
3221 You will want to look into zconf.h to tell zlib (and thus libpng) that
3222 it cannot allocate more then 64K at a time. Even if you can, the memory
3223 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3225 .SS Configuring for DOS
3227 For DOS users who only have access to the lower 640K, you will
3228 have to limit zlib's memory usage via a png_set_compression_mem_level()
3229 call. See zlib.h or zconf.h in the zlib library for more information.
3231 .SS Configuring for Medium Model
3233 Libpng's support for medium model has been tested on most of the popular
3234 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3235 defined, and FAR gets defined to far in pngconf.h, and you should be
3236 all set. Everything in the library (except for zlib's structure) is
3237 expecting far data. You must use the typedefs with the p or pp on
3238 the end for pointers (or at least look at them and be careful). Make
3239 note that the rows of data are defined as png_bytepp, which is an
3240 unsigned char far * far *.
3242 .SS Configuring for gui/windowing platforms:
3244 You will need to write new error and warning functions that use the GUI
3245 interface, as described previously, and set them to be the error and
3246 warning functions at the time that png_create_*_struct() is called,
3247 in order to have them available during the structure initialization.
3248 They can be changed later via png_set_error_fn(). On some compilers,
3249 you may also have to change the memory allocators (png_malloc, etc.).
3251 .SS Configuring for compiler xxx:
3253 All includes for libpng are in pngconf.h. If you need to add/change/delete
3254 an include, this is the place to do it. The includes that are not
3255 needed outside libpng are protected by the PNG_INTERNAL definition,
3256 which is only defined for those routines inside libpng itself. The
3257 files in libpng proper only include png.h, which includes pngconf.h.
3259 .SS Configuring zlib:
3261 There are special functions to configure the compression. Perhaps the
3262 most useful one changes the compression level, which currently uses
3263 input compression values in the range 0 - 9. The library normally
3264 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3265 have shown that for a large majority of images, compression values in
3266 the range 3-6 compress nearly as well as higher levels, and do so much
3267 faster. For online applications it may be desirable to have maximum speed
3268 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3269 specify no compression (Z_NO_COMPRESSION = 0), but this would create
3270 files larger than just storing the raw bitmap. You can specify the
3271 compression level by calling:
3273 png_set_compression_level(png_ptr, level);
3275 Another useful one is to reduce the memory level used by the library.
3276 The memory level defaults to 8, but it can be lowered if you are
3277 short on memory (running DOS, for example, where you only have 640K).
3278 Note that the memory level does have an effect on compression; among
3279 other things, lower levels will result in sections of incompressible
3280 data being emitted in smaller stored blocks, with a correspondingly
3281 larger relative overhead of up to 15% in the worst case.
3283 png_set_compression_mem_level(png_ptr, level);
3285 The other functions are for configuring zlib. They are not recommended
3286 for normal use and may result in writing an invalid PNG file. See
3287 zlib.h for more information on what these mean.
3289 png_set_compression_strategy(png_ptr,
3291 png_set_compression_window_bits(png_ptr,
3293 png_set_compression_method(png_ptr, method);
3294 png_set_compression_buffer_size(png_ptr, size);
3296 .SS Controlling row filtering
3298 If you want to control whether libpng uses filtering or not, which
3299 filters are used, and how it goes about picking row filters, you
3300 can call one of these functions. The selection and configuration
3301 of row filters can have a significant impact on the size and
3302 encoding speed and a somewhat lesser impact on the decoding speed
3303 of an image. Filtering is enabled by default for RGB and grayscale
3304 images (with and without alpha), but not for paletted images nor
3305 for any images with bit depths less than 8 bits/pixel.
3307 The 'method' parameter sets the main filtering method, which is
3308 currently only '0' in the PNG 1.2 specification. The 'filters'
3309 parameter sets which filter(s), if any, should be used for each
3310 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3311 to turn filtering on and off, respectively.
3313 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3314 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3315 ORed together with '|' to specify one or more filters to use.
3316 These filters are described in more detail in the PNG specification.
3317 If you intend to change the filter type during the course of writing
3318 the image, you should start with flags set for all of the filters
3319 you intend to use so that libpng can initialize its internal
3320 structures appropriately for all of the filter types. (Note that this
3321 means the first row must always be adaptively filtered, because libpng
3322 currently does not allocate the filter buffers until png_write_row()
3323 is called for the first time.)
3325 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3326 PNG_FILTER_UP | PNG_FILTER_AVE |
3327 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3329 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3331 The second parameter can also be
3332 PNG_INTRAPIXEL_DIFFERENCING if you are
3333 writing a PNG to be embedded in a MNG
3334 datastream. This parameter must be the
3335 same as the value of filter_method used
3338 It is also possible to influence how libpng chooses from among the
3339 available filters. This is done in one or both of two ways - by
3340 telling it how important it is to keep the same filter for successive
3341 rows, and by telling it the relative computational costs of the filters.
3343 double weights[3] = {1.5, 1.3, 1.1},
3344 costs[PNG_FILTER_VALUE_LAST] =
3345 {1.0, 1.3, 1.3, 1.5, 1.7};
3347 png_set_filter_heuristics(png_ptr,
3348 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3351 The weights are multiplying factors that indicate to libpng that the
3352 row filter should be the same for successive rows unless another row filter
3353 is that many times better than the previous filter. In the above example,
3354 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3355 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
3356 and still be chosen, while the NONE filter could have a sum 1.1 times
3357 higher than other filters and still be chosen. Unspecified weights are
3358 taken to be 1.0, and the specified weights should probably be declining
3359 like those above in order to emphasize recent filters over older filters.
3361 The filter costs specify for each filter type a relative decoding cost
3362 to be considered when selecting row filters. This means that filters
3363 with higher costs are less likely to be chosen over filters with lower
3364 costs, unless their "sum of absolute differences" is that much smaller.
3365 The costs do not necessarily reflect the exact computational speeds of
3366 the various filters, since this would unduly influence the final image
3369 Note that the numbers above were invented purely for this example and
3370 are given only to help explain the function usage. Little testing has
3371 been done to find optimum values for either the costs or the weights.
3373 .SS Removing unwanted object code
3375 There are a bunch of #define's in pngconf.h that control what parts of
3376 libpng are compiled. All the defines end in _SUPPORTED. If you are
3377 never going to use a capability, you can change the #define to #undef
3378 before recompiling libpng and save yourself code and data space, or
3379 you can turn off individual capabilities with defines that begin with
3382 You can also turn all of the transforms and ancillary chunk capabilities
3383 off en masse with compiler directives that define
3384 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3386 along with directives to turn on any of the capabilities that you do
3387 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3388 the extra transformations but still leave the library fully capable of reading
3389 and writing PNG files with all known public chunks
3390 Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3391 produces a library that is incapable of reading or writing ancillary chunks.
3392 If you are not using the progressive reading capability, you can
3393 turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3394 this with the INTERLACING capability, which you'll still have).
3396 All the reading and writing specific code are in separate files, so the
3397 linker should only grab the files it needs. However, if you want to
3398 make sure, or if you are building a stand alone library, all the
3399 reading files start with pngr and all the writing files start with
3400 pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3401 are used for both reading and writing, and always need to be included.
3402 The progressive reader is in pngpread.c
3404 If you are creating or distributing a dynamically linked library (a .so
3405 or DLL file), you should not remove or disable any parts of the library,
3406 as this will cause applications linked with different versions of the
3407 library to fail if they call functions not available in your library.
3408 The size of the library itself should not be an issue, because only
3409 those sections that are actually used will be loaded into memory.
3411 .SS Requesting debug printout
3413 The macro definition PNG_DEBUG can be used to request debugging
3414 printout. Set it to an integer value in the range 0 to 3. Higher
3415 numbers result in increasing amounts of debugging information. The
3416 information is printed to the "stderr" file, unless another file
3417 name is specified in the PNG_DEBUG_FILE macro definition.
3419 When PNG_DEBUG > 0, the following functions (macros) become available:
3421 png_debug(level, message)
3422 png_debug1(level, message, p1)
3423 png_debug2(level, message, p1, p2)
3425 in which "level" is compared to PNG_DEBUG to decide whether to print
3426 the message, "message" is the formatted string to be printed,
3427 and p1 and p2 are parameters that are to be embedded in the string
3428 according to printf-style formatting directives. For example,
3430 png_debug1(2, "foo=%d\n", foo);
3435 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3437 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3438 can still use PNG_DEBUG to control your own debugging:
3444 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3445 having level = 0 will be printed. There aren't any such statements in
3446 this version of libpng, but if you insert some they will be printed.
3448 .SH VI. Runtime optimization
3450 A new feature in libpng 1.2.0 is the ability to dynamically switch between
3451 standard and optimized versions of some routines. Currently these are
3452 limited to three computationally intensive tasks when reading PNG files:
3453 decoding row filters, expanding interlacing, and combining interlaced or
3454 transparent row data with previous row data. Currently the optimized
3455 versions are available only for x86 (Intel, AMD, etc.) platforms with
3456 MMX support, though this may change in future versions. (For example,
3457 the non-MMX assembler optimizations for zlib might become similarly
3458 runtime-selectable in future releases, in which case libpng could be
3459 extended to support them. Alternatively, the compile-time choice of
3460 floating-point versus integer routines for gamma correction might become
3461 runtime-selectable.)
3463 Because such optimizations tend to be very platform- and compiler-dependent,
3464 both in how they are written and in how they perform, the new runtime code
3465 in libpng has been written to allow programs to query, enable, and disable
3466 either specific optimizations or all such optimizations. For example, to
3467 enable all possible optimizations (bearing in mind that some "optimizations"
3468 may actually run more slowly in rare cases):
3470 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3471 png_uint_32 mask, flags;
3473 flags = png_get_asm_flags(png_ptr);
3474 mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3475 png_set_asm_flags(png_ptr, flags | mask);
3478 To enable only optimizations relevant to reading PNGs, use PNG_SELECT_READ
3479 by itself when calling png_get_asm_flagmask(); similarly for optimizing
3480 only writing. To disable all optimizations:
3482 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3483 flags = png_get_asm_flags(png_ptr);
3484 mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3485 png_set_asm_flags(png_ptr, flags & ~mask);
3488 To enable or disable only MMX-related features, use png_get_mmx_flagmask()
3489 in place of png_get_asm_flagmask(). The mmx version takes one additional
3492 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3493 int selection = PNG_SELECT_READ | PNG_SELECT_WRITE;
3496 mask = png_get_mmx_flagmask(selection, &compilerID);
3499 On return, compilerID will indicate which version of the MMX assembler
3500 optimizations was compiled. Currently two flavors exist: Microsoft
3501 Visual C++ (compilerID == 1) and GNU C (a.k.a. gcc/gas, compilerID == 2).
3502 On non-x86 platforms or on systems compiled without MMX optimizations, a
3503 value of -1 is used.
3505 Note that both png_get_asm_flagmask() and png_get_mmx_flagmask() return
3506 all valid, settable optimization bits for the version of the library that's
3507 currently in use. In the case of shared (dynamically linked) libraries,
3508 this may include optimizations that did not exist at the time the code was
3509 written and compiled. It is also possible, of course, to enable only known,
3510 specific optimizations; for example:
3512 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3513 flags = PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3514 | PNG_ASM_FLAG_MMX_READ_INTERLACE \
3515 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3516 | PNG_ASM_FLAG_MMX_READ_FILTER_UP \
3517 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3518 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH ;
3519 png_set_asm_flags(png_ptr, flags);
3522 This method would enable only the MMX read-optimizations available at the
3523 time of libpng 1.2.0's release, regardless of whether a later version of
3524 the DLL were actually being used. (Also note that these functions did not
3525 exist in versions older than 1.2.0, so any attempt to run a dynamically
3526 linked app on such an older version would fail.)
3528 To determine whether the processor supports MMX instructions at all, use
3529 the png_mmx_support() function:
3531 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3532 mmxsupport = png_mmx_support();
3535 It returns -1 if MMX support is not compiled into libpng, 0 if MMX code
3536 is compiled but MMX is not supported by the processor, or 1 if MMX support
3537 is fully available. Note that png_mmx_support(), png_get_mmx_flagmask(),
3538 and png_get_asm_flagmask() all may be called without allocating and ini-
3539 tializing any PNG structures (for example, as part of a usage screen or
3542 The following code can be used to prevent an application from using the
3543 thread_unsafe features, even if libpng was built with PNG_THREAD_UNSAFE_OK
3546 #if defined(PNG_USE_PNGGCCRD) && defined(PNG_ASSEMBLER_CODE_SUPPORTED) \
3547 && defined(PNG_THREAD_UNSAFE_OK)
3548 /* Disable thread-unsafe features of pnggccrd */
3549 if (png_access_version() >= 10200)
3551 png_uint_32 mmx_disable_mask = 0;
3552 png_uint_32 asm_flags;
3554 mmx_disable_mask |= ( PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3555 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3556 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3557 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH );
3558 asm_flags = png_get_asm_flags(png_ptr);
3559 png_set_asm_flags(png_ptr, asm_flags & ~mmx_disable_mask);
3563 For more extensive examples of runtime querying, enabling and disabling
3564 of optimized features, see contrib/gregbook/readpng2.c in the libpng
3565 source-code distribution.
3568 .SH VII. MNG support
3570 The MNG specification (available at http://www.libpng.org/pub/mng) allows
3571 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3572 Libpng can support some of these extensions. To enable them, use the
3573 png_permit_mng_features() function:
3575 feature_set = png_permit_mng_features(png_ptr, mask)
3576 mask is a png_uint_32 containing the logical OR of the
3577 features you want to enable. These include
3578 PNG_FLAG_MNG_EMPTY_PLTE
3579 PNG_FLAG_MNG_FILTER_64
3580 PNG_ALL_MNG_FEATURES
3581 feature_set is a png_32_uint that is the logical AND of
3582 your mask with the set of MNG features that is
3583 supported by the version of libpng that you are using.
3585 It is an error to use this function when reading or writing a standalone
3586 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3587 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3588 and the MHDR and MEND chunks. Libpng does not provide support for these
3589 or any other MNG chunks; your application must provide its own support for
3590 them. You may wish to consider using libmng (available at
3591 http://www.libmng.com) instead.
3593 .SH VIII. Changes to Libpng from version 0.88
3595 It should be noted that versions of libpng later than 0.96 are not
3596 distributed by the original libpng author, Guy Schalnat, nor by
3597 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3598 distributed versions 0.89 through 0.96, but rather by another member
3599 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3600 still alive and well, but they have moved on to other things.
3602 The old libpng functions png_read_init(), png_write_init(),
3603 png_info_init(), png_read_destroy(), and png_write_destroy() have been
3604 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3605 functions will be removed from libpng version 2.0.0.
3607 The preferred method of creating and initializing the libpng structures is
3608 via the png_create_read_struct(), png_create_write_struct(), and
3609 png_create_info_struct() because they isolate the size of the structures
3610 from the application, allow version error checking, and also allow the
3611 use of custom error handling routines during the initialization, which
3612 the old functions do not. The functions png_read_destroy() and
3613 png_write_destroy() do not actually free the memory that libpng
3614 allocated for these structs, but just reset the data structures, so they
3615 can be used instead of png_destroy_read_struct() and
3616 png_destroy_write_struct() if you feel there is too much system overhead
3617 allocating and freeing the png_struct for each image read.
3619 Setting the error callbacks via png_set_message_fn() before
3620 png_read_init() as was suggested in libpng-0.88 is no longer supported
3621 because this caused applications that do not use custom error functions
3622 to fail if the png_ptr was not initialized to zero. It is still possible
3623 to set the error callbacks AFTER png_read_init(), or to change them with
3624 png_set_error_fn(), which is essentially the same function, but with a new
3625 name to force compilation errors with applications that try to use the old
3628 Starting with version 1.0.7, you can find out which version of the library
3629 you are using at run-time:
3631 png_uint_32 libpng_vn = png_access_version_number();
3633 The number libpng_vn is constructed from the major version, minor
3634 version with leading zero, and release number with leading zero,
3635 (e.g., libpng_vn for version 1.0.7 is 10007).
3637 You can also check which version of png.h you used when compiling your
3640 png_uint_32 application_vn = PNG_LIBPNG_VER;
3642 .SH IX. Y2K Compliance in libpng
3646 Since the PNG Development group is an ad-hoc body, we can't make
3647 an official declaration.
3649 This is your unofficial assurance that libpng from version 0.71 and
3650 upward through 1.2.5 are Y2K compliant. It is my belief that earlier
3651 versions were also Y2K compliant.
3653 Libpng only has three year fields. One is a 2-byte unsigned integer that
3654 will hold years up to 65535. The other two hold the date in text
3655 format, and will hold years up to 9999.
3658 "png_uint_16 year" in png_time_struct.
3661 "png_charp time_buffer" in png_struct and
3662 "near_time_buffer", which is a local character string in png.c.
3664 There are seven time-related functions:
3666 png_convert_to_rfc_1123() in png.c
3667 (formerly png_convert_to_rfc_1152() in error)
3668 png_convert_from_struct_tm() in pngwrite.c, called
3670 png_convert_from_time_t() in pngwrite.c
3671 png_get_tIME() in pngget.c
3672 png_handle_tIME() in pngrutil.c, called in pngread.c
3673 png_set_tIME() in pngset.c
3674 png_write_tIME() in pngwutil.c, called in pngwrite.c
3676 All appear to handle dates properly in a Y2K environment. The
3677 png_convert_from_time_t() function calls gmtime() to convert from system
3678 clock time, which returns (year - 1900), which we properly convert to
3679 the full 4-digit year. There is a possibility that applications using
3680 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
3681 function, or that they are incorrectly passing only a 2-digit year
3682 instead of "year - 1900" into the png_convert_from_struct_tm() function,
3683 but this is not under our control. The libpng documentation has always
3684 stated that it works with 4-digit years, and the APIs have been
3687 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3688 integer to hold the year, and can hold years as large as 65535.
3690 zlib, upon which libpng depends, is also Y2K compliant. It contains
3691 no date-related code.
3694 Glenn Randers-Pehrson
3696 PNG Development Group
3700 Note about libpng version numbers:
3702 Due to various miscommunications, unforeseen code incompatibilities
3703 and occasional factors outside the authors' control, version numbering
3704 on the library has not always been consistent and straightforward.
3705 The following table summarizes matters since version 0.89c, which was
3706 the first widely used release:
3708 source png.h png.h shared-lib
3709 version string int version
3710 ------- ------ ----- ----------
3711 0.89c ("beta 3") 0.89 89 1.0.89
3712 0.90 ("beta 4") 0.90 90 0.90
3713 0.95 ("beta 5") 0.95 95 0.95
3714 0.96 ("beta 6") 0.96 96 0.96
3715 0.97b ("beta 7") 1.00.97 97 1.0.1
3716 0.97c 0.97 97 2.0.97
3719 0.99a-m 0.99 99 2.0.99
3721 1.0.0 1.0.0 100 2.1.0
3722 1.0.0 (from here on, the 100 2.1.0
3723 1.0.1 png.h string is 10001 2.1.0
3724 1.0.1a-e identical to the 10002 from here on, the
3725 1.0.2 source version) 10002 shared library is 2.V
3726 1.0.2a-b 10003 where V is the source
3727 1.0.1 10001 code version except as
3728 1.0.1a-e 10002 2.1.0.1a-e noted.
3730 1.0.2a-b 10003 2.1.0.2a-b
3732 1.0.3a-d 10004 2.1.0.3a-d
3734 1.0.4a-f 10005 2.1.0.4a-f
3735 1.0.5 (+ 2 patches) 10005 2.1.0.5
3736 1.0.5a-d 10006 2.1.0.5a-d
3737 1.0.5e-r 10100 2.1.0.5e-r
3738 1.0.5s-v 10006 2.1.0.5s-v
3739 1.0.6 (+ 3 patches) 10006 2.1.0.6
3740 1.0.6d-g 10007 2.1.0.6d-g
3743 1.0.6j 10007 2.1.0.6j
3744 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3745 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3746 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3747 1.0.7 1 10007 2.1.0.7
3748 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3749 1.0.8rc1 1 10008 2.1.0.8rc1
3750 1.0.8 1 10008 2.1.0.8
3751 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3752 1.0.9rc1 1 10009 2.1.0.9rc1
3753 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3754 1.0.9rc2 1 10009 2.1.0.9rc2
3755 1.0.9 1 10009 2.1.0.9
3756 1.0.10beta1 1 10010 2.1.0.10beta1
3757 1.0.10rc1 1 10010 2.1.0.10rc1
3758 1.0.10 1 10010 2.1.0.10
3759 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3760 1.0.11rc1 1 10011 2.1.0.11rc1
3761 1.0.11 1 10011 2.1.0.11
3762 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3763 1.0.12rc1 2 10012 2.1.0.12rc1
3764 1.0.12 2 10012 2.1.0.12
3765 1.1.0a-f - 10100 2.1.1.0a-f abandoned
3766 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3767 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
3768 1.2.0rc1 3 10200 3.1.2.0rc1
3769 1.2.0 3 10200 3.1.2.0
3770 1.2.1beta-4 3 10201 3.1.2.1beta1-4
3771 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
3772 1.2.1 3 10201 3.1.2.1
3773 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
3774 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
3775 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
3776 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
3777 1.0.13 10 10013 10.so.0.1.0.13
3778 1.2.2 12 10202 12.so.0.1.2.2
3779 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
3780 1.2.3 12 10203 12.so.0.1.2.3
3781 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
3782 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
3783 1.0.14 10 10014 10.so.0.1.0.14
3784 1.2.4 13 10204 12.so.0.1.2.4
3785 1.0.15rc1-3 10 10015 10.so.0.1.0.15rc1-3
3786 1.2.5rc1-3 13 10205 12.so.0.1.2.5rc1-3
3787 1.0.15 10 10015 10.so.0.1.0.15
3788 1.2.5 13 10205 12.so.0.1.2.5
3790 Henceforth the source version will match the shared-library minor
3791 and patch numbers; the shared-library major version number will be
3792 used for changes in backward compatibility, as it is intended. The
3793 PNG_PNGLIB_VER macro, which is not used within libpng but is available
3794 for applications, is an unsigned integer of the form xyyzz corresponding
3795 to the source version x.y.z (leading zeros in y and z). Beta versions
3796 were given the previous public release number plus a letter, until
3797 version 1.0.6j; from then on they were given the upcoming public
3798 release number plus "betaNN" or "rcN".
3805 ftp://ftp.uu.net/graphics/png
3806 http://www.libpng.org/pub/png
3811 (generally) at the same location as
3815 ftp://ftp.uu.net/pub/archiving/zip/zlib
3817 ftp://ftp.info-zip.org/pub/infozip/zlib
3820 .IR PNG specification: RFC 2083
3822 (generally) at the same location as
3826 ftp://ds.internic.net/rfc/rfc2083.txt
3828 or (as a W3C Recommendation) at
3830 http://www.w3.org/TR/REC-png.html
3833 In the case of any inconsistency between the PNG specification
3834 and this library, the specification takes precedence.
3837 This man page: Glenn Randers-Pehrson
3838 <randeg@alum.rpi.edu>
3840 The contributing authors would like to thank all those who helped
3841 with testing, bug fixes, and patience. This wouldn't have been
3842 possible without all of you.
3844 Thanks to Frank J. T. Wojcik for helping with the documentation.
3846 Libpng version 1.2.5 - October 3, 2002:
3847 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
3848 Currently maintained by Glenn Randers-Pehrson (randeg@alum.rpi.edu).
3850 Supported by the PNG development group
3852 (png-implement@ccrc.wustl.edu).
3854 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
3856 (This copy of the libpng notices is provided for your convenience. In case of
3857 any discrepancy between this copy and the notices in the file png.h that is
3858 included in the libpng distribution, the latter shall prevail.)
3860 If you modify libpng you may insert additional notices immediately following
3863 libpng versions 1.0.7, July 1, 2000, through 1.2.5, October 3, 2002, are
3864 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
3865 distributed according to the same disclaimer and license as libpng-1.0.6
3866 with the following individuals added to the list of Contributing Authors
3868 Simon-Pierre Cadieux
3872 and with the following additions to the disclaimer:
3874 There is no warranty against interference with your
3875 enjoyment of the library or against infringement.
3876 There is no warranty that our efforts or the library
3877 will fulfill any of your particular purposes or needs.
3878 This library is provided with all faults, and the entire
3879 risk of satisfactory quality, performance, accuracy, and
3880 effort is with the user.
3882 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
3883 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
3884 Distributed according to the same disclaimer and license as libpng-0.96,
3885 with the following individuals added to the list of Contributing Authors:
3888 Glenn Randers-Pehrson
3891 libpng versions 0.89, June 1996, through 0.96, May 1997, are
3892 Copyright (c) 1996, 1997 Andreas Dilger
3893 Distributed according to the same disclaimer and license as libpng-0.88,
3894 with the following individuals added to the list of Contributing Authors:
3903 libpng versions 0.5, May 1995, through 0.88, January 1996, are
3904 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
3906 For the purposes of this copyright and license, "Contributing Authors"
3907 is defined as the following set of individuals:
3915 The PNG Reference Library is supplied "AS IS". The Contributing Authors
3916 and Group 42, Inc. disclaim all warranties, expressed or implied,
3917 including, without limitation, the warranties of merchantability and of
3918 fitness for any purpose. The Contributing Authors and Group 42, Inc.
3919 assume no liability for direct, indirect, incidental, special, exemplary,
3920 or consequential damages, which may result from the use of the PNG
3921 Reference Library, even if advised of the possibility of such damage.
3923 Permission is hereby granted to use, copy, modify, and distribute this
3924 source code, or portions hereof, for any purpose, without fee, subject
3925 to the following restrictions:
3927 1. The origin of this source code must not be misrepresented.
3929 2. Altered versions must be plainly marked as such and
3930 must not be misrepresented as being the original source.
3932 3. This Copyright notice may not be removed or altered from
3933 any source or altered source distribution.
3935 The Contributing Authors and Group 42, Inc. specifically permit, without
3936 fee, and encourage the use of this source code as a component to
3937 supporting the PNG file format in commercial products. If you use this
3938 source code in a product, acknowledgment is not required but would be
3942 A "png_get_copyright" function is available, for convenient use in "about"
3945 printf("%s",png_get_copyright(NULL));
3947 Also, the PNG logo (in PNG format, of course) is supplied in the
3948 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
3950 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
3951 certification mark of the Open Source Initiative.
3953 Glenn Randers-Pehrson
projects / synfig.git / blob