1 .TH LIBPNG 3 "August 15, 2004"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.2.6
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_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
107 \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
111 \fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
115 \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
119 \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
123 \fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
127 \fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
131 \fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
135 \fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
139 \fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
143 \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
147 \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
151 \fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
155 \fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
159 \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
163 \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
167 \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
171 \fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
175 \fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
179 \fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
183 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
187 \fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
191 \fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
195 \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
199 \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
203 \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
207 \fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
211 \fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
215 \fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
219 \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
223 \fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
225 \fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
229 \fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
233 \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
237 \fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
241 \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
245 \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
249 \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
253 \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
257 \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
261 \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
265 \fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
269 \fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
273 \fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
277 \fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
281 \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
285 \fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
289 \fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
293 \fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
297 \fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
301 \fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
305 \fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
309 \fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
313 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
317 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
321 \fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
325 \fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
329 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
333 \fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
337 \fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
341 \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
345 \fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
349 \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
353 \fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
357 \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
361 \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
365 \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
369 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
373 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
377 \fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
381 \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
385 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
389 \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
393 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
397 \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
401 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
405 \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
409 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
413 \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
417 \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
421 \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
425 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
429 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
433 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
437 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
441 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
445 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
449 \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
453 \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
457 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
461 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
465 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
469 \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
473 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
477 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
481 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
485 \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
489 \fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
493 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
497 \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
501 \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
505 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
509 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
513 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
517 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
521 \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
525 \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
529 \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
533 \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
537 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
541 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
545 \fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
549 \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
553 \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
557 \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
561 \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
565 \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
569 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
573 \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
577 \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
581 \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
585 \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
589 \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
593 \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
597 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
601 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
605 \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
609 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
613 \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
617 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
621 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
625 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
629 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
633 \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
637 \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
641 \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
645 \fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
649 \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
653 \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
657 \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
661 \fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
665 \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
669 \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
673 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
677 \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
681 \fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
685 \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
689 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
693 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
697 \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
701 \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
705 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
709 \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
713 \fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
717 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
721 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
725 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
729 \fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
733 \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
737 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
741 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
745 \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
749 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
753 \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
757 \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
761 \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
768 library supports encoding, decoding, and various manipulations of
769 the Portable Network Graphics (PNG) format image files. It uses the
772 Following is a copy of the libpng.txt file that accompanies libpng.
774 libpng.txt - A description on how to use and modify libpng
776 libpng version 1.2.6 - August 15, 2004
777 Updated and distributed by Glenn Randers-Pehrson
778 <glennrp@users.sourceforge.net>
779 Copyright (c) 1998-2004 Glenn Randers-Pehrson
780 For conditions of distribution and use, see copyright
785 libpng 1.0 beta 6 version 0.96 May 28, 1997
786 Updated and distributed by Andreas Dilger
787 Copyright (c) 1996, 1997 Andreas Dilger
789 libpng 1.0 beta 2 - version 0.88 January 26, 1996
790 For conditions of distribution and use, see copyright
791 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
792 Schalnat, Group 42, Inc.
794 Updated/rewritten per request in the libpng FAQ
795 Copyright (c) 1995, 1996 Frank J. T. Wojcik
796 December 18, 1995 & January 20, 1996
800 This file describes how to use and modify the PNG reference library
801 (known as libpng) for your own use. There are five sections to this
802 file: introduction, structures, reading, writing, and modification and
803 configuration notes for various special platforms. In addition to this
804 file, example.c is a good starting point for using the library, as
805 it is heavily commented and should include everything most people
806 will need. We assume that libpng is already installed; see the
807 INSTALL file for instructions on how to install libpng.
809 Libpng was written as a companion to the PNG specification, as a way
810 of reducing the amount of time and effort it takes to support the PNG
811 file format in application programs.
813 The PNG-1.2 specification is available at <http://www.libpng.org/pub/png>
814 and at <ftp://ftp.uu.net/graphics/png/documents/>.
816 The PNG-1.0 specification is available
817 as RFC 2083 <ftp://ftp.uu.net/graphics/png/documents/> and as a
818 W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
819 additional chunks are described in the special-purpose public chunks
820 documents at <ftp://ftp.uu.net/graphics/png/documents/>.
823 about PNG, and the latest version of libpng, can be found at the PNG home
824 page, <http://www.libpng.org/pub/png/>
825 and at <ftp://ftp.uu.net/graphics/png/>.
827 Most users will not have to modify the library significantly; advanced
828 users may want to modify it more. All attempts were made to make it as
829 complete as possible, while keeping the code easy to understand.
830 Currently, this library only supports C. Support for other languages
833 Libpng has been designed to handle multiple sessions at one time,
834 to be easily modifiable, to be portable to the vast majority of
835 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
836 to use. The ultimate goal of libpng is to promote the acceptance of
837 the PNG file format in whatever way possible. While there is still
838 work to be done (see the TODO file), libpng should cover the
839 majority of the needs of its users.
841 Libpng uses zlib for its compression and decompression of PNG files.
842 Further information about zlib, and the latest version of zlib, can
843 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
844 The zlib compression utility is a general purpose utility that is
845 useful for more than PNG files, and can be used without libpng.
846 See the documentation delivered with zlib for more details.
847 You can usually find the source files for the zlib utility wherever you
848 find the libpng source files.
850 Libpng is thread safe, provided the threads are using different
851 instances of the structures. Each thread should have its own
852 png_struct and png_info instances, and thus its own image.
853 Libpng does not protect itself against two threads using the
854 same instance of a structure. Note: thread safety may be defeated
855 by use of some of the MMX assembler code in pnggccrd.c, which is only
856 compiled when the user defines PNG_THREAD_UNSAFE_OK.
861 There are two main structures that are important to libpng, png_struct
862 and png_info. The first, png_struct, is an internal structure that
863 will not, for the most part, be used by a user except as the first
864 variable passed to every libpng function call.
866 The png_info structure is designed to provide information about the
867 PNG file. At one time, the fields of png_info were intended to be
868 directly accessible to the user. However, this tended to cause problems
869 with applications using dynamically loaded libraries, and as a result
870 a set of interface functions for png_info (the png_get_*() and png_set_*()
871 functions) was developed. The fields of png_info are still available for
872 older applications, but it is suggested that applications use the new
873 interfaces if at all possible.
875 Applications that do make direct access to the members of png_struct (except
876 for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
877 and applications that make direct access to the members of png_info must
878 be recompiled if they were compiled or loaded with libpng version 1.0.6,
879 in which the members were in a different order. In version 1.0.7, the
880 members of the png_info structure reverted to the old order, as they were
881 in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
882 structures are going to be hidden, and the contents of the structures will
883 only be accessible through the png_get/png_set functions.
885 The png.h header file is an invaluable reference for programming with libpng.
886 And while I'm on the topic, make sure you include the libpng header file:
892 We'll now walk you through the possible functions to call when reading
893 in a PNG file sequentially, briefly explaining the syntax and purpose
894 of each one. See example.c and png.h for more detail. While
895 progressive reading is covered in the next section, you will still
896 need some of the functions discussed in this section to read a PNG
901 You will want to do the I/O initialization(*) before you get into libpng,
902 so if it doesn't work, you don't have much to undo. Of course, you
903 will also want to insure that you are, in fact, dealing with a PNG
904 file. Libpng provides a simple check to see if a file is a PNG file.
905 To use it, pass in the first 1 to 8 bytes of the file to the function
906 png_sig_cmp(), and it will return 0 if the bytes match the corresponding
907 bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
908 you pass in, the greater the accuracy of the prediction.
910 If you are intending to keep the file pointer open for use in libpng,
911 you must ensure you don't read more than 8 bytes from the beginning
912 of the file, and you also have to make a call to png_set_sig_bytes_read()
913 with the number of bytes you read from the beginning. Libpng will
914 then only check the bytes (if any) that your program didn't read.
916 (*): If you are not using the standard I/O functions, you will need
917 to replace them with custom functions. See the discussion under
921 FILE *fp = fopen(file_name, "rb");
926 fread(header, 1, number, fp);
927 is_png = !png_sig_cmp(header, 0, number);
934 Next, png_struct and png_info need to be allocated and initialized. In
935 order to ensure that the size of these structures is correct even with a
936 dynamically linked libpng, there are functions to initialize and
937 allocate the structures. We also pass the library version, optional
938 pointers to error handling functions, and a pointer to a data struct for
939 use by the error functions, if necessary (the pointer and functions can
940 be NULL if the default error handlers are to be used). See the section
941 on Changes to Libpng below regarding the old initialization functions.
942 The structure allocation functions quietly return NULL if they fail to
943 create the structure, so your application should check for that.
945 png_structp png_ptr = png_create_read_struct
946 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
947 user_error_fn, user_warning_fn);
951 png_infop info_ptr = png_create_info_struct(png_ptr);
954 png_destroy_read_struct(&png_ptr,
955 (png_infopp)NULL, (png_infopp)NULL);
959 png_infop end_info = png_create_info_struct(png_ptr);
962 png_destroy_read_struct(&png_ptr, &info_ptr,
967 If you want to use your own memory allocation routines,
968 define PNG_USER_MEM_SUPPORTED and use
969 png_create_read_struct_2() instead of png_create_read_struct():
971 png_structp png_ptr = png_create_read_struct_2
972 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
973 user_error_fn, user_warning_fn, (png_voidp)
974 user_mem_ptr, user_malloc_fn, user_free_fn);
976 The error handling routines passed to png_create_read_struct()
977 and the memory alloc/free routines passed to png_create_struct_2()
978 are only necessary if you are not using the libpng supplied error
979 handling and memory alloc/free functions.
981 When libpng encounters an error, it expects to longjmp back
982 to your routine. Therefore, you will need to call setjmp and pass
983 your png_jmpbuf(png_ptr). If you read the file from different
984 routines, you will need to update the jmpbuf field every time you enter
985 a new routine that will call a png_*() function.
987 See your documentation of setjmp/longjmp for your compiler for more
988 information on setjmp/longjmp. See the discussion on libpng error
989 handling in the Customizing Libpng section below for more information
990 on the libpng error handling. If an error occurs, and libpng longjmp's
991 back to your setjmp, you will want to call png_destroy_read_struct() to
994 if (setjmp(png_jmpbuf(png_ptr)))
996 png_destroy_read_struct(&png_ptr, &info_ptr,
1002 If you would rather avoid the complexity of setjmp/longjmp issues,
1003 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
1004 errors will result in a call to PNG_ABORT() which defaults to abort().
1006 Now you need to set up the input code. The default for libpng is to
1007 use the C function fread(). If you use this, you will need to pass a
1008 valid FILE * in the function png_init_io(). Be sure that the file is
1009 opened in binary mode. If you wish to handle reading data in another
1010 way, you need not call the png_init_io() function, but you must then
1011 implement the libpng I/O methods discussed in the Customizing Libpng
1014 png_init_io(png_ptr, fp);
1016 If you had previously opened the file and read any of the signature from
1017 the beginning in order to see if this was a PNG file, you need to let
1018 libpng know that there are some bytes missing from the start of the file.
1020 png_set_sig_bytes(png_ptr, number);
1022 .SS Setting up callback code
1024 You can set up a callback function to handle any unknown chunks in the
1025 input stream. You must supply the function
1027 read_chunk_callback(png_ptr ptr,
1028 png_unknown_chunkp chunk);
1030 /* The unknown chunk structure contains your
1035 /* Note that libpng has already taken care of
1038 /* put your code here. Return one of the
1041 return (-n); /* chunk had an error */
1042 return (0); /* did not recognize */
1043 return (n); /* success */
1046 (You can give your function another name that you like instead of
1047 "read_chunk_callback")
1049 To inform libpng about your function, use
1051 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1052 read_chunk_callback);
1054 This names not only the callback function, but also a user pointer that
1055 you can retrieve with
1057 png_get_user_chunk_ptr(png_ptr);
1059 At this point, you can set up a callback function that will be
1060 called after each row has been read, which you can use to control
1061 a progress meter or the like. It's demonstrated in pngtest.c.
1062 You must supply a function
1064 void read_row_callback(png_ptr ptr, png_uint_32 row,
1067 /* put your code here */
1070 (You can give it another name that you like instead of "read_row_callback")
1072 To inform libpng about your function, use
1074 png_set_read_status_fn(png_ptr, read_row_callback);
1076 %-%.SS Width and height limits
1078 %-%The PNG specification allows the width and height of an image to be as
1079 %-%large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1080 %-%Since very few applications really need to process such large images,
1081 %-%we have imposed an arbitrary 1-million limit on rows and columns.
1082 %-%Larger images will be rejected immediately with a png_error() call. If
1083 %-%you wish to override this limit, you can use
1085 %-% png_set_user_limits(png_ptr, width_max, height_max);
1087 %-%to set your own limits, or use width_max = height_max = 0x7fffffffL
1088 %-%to allow all valid dimensions (libpng may reject some very large images
1089 %-%anyway because of potential buffer overflow conditions).
1091 %-%You should put this statement after you create the PNG structure and
1092 %-%before calling png_read_info(), png_read_png(), or png_process_data().
1093 %-%If you need to retrieve the limits that are being applied, use
1095 %-% width_max = png_get_user_width_max(png_ptr);
1096 %-% height_max = png_get_user_height_max(png_ptr);
1098 .SS Unknown-chunk handling
1100 Now you get to set the way the library processes unknown chunks in the
1101 input PNG stream. Both known and unknown chunks will be read. Normal
1102 behavior is that known chunks will be parsed into information in
1103 various info_ptr members; unknown chunks will be discarded. To change
1106 png_set_keep_unknown_chunks(png_ptr, keep,
1107 chunk_list, num_chunks);
1108 keep - 0: do not handle as unknown
1110 2: keep only if safe-to-copy
1111 3: keep even if unsafe-to-copy
1112 You can use these definitions:
1113 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1114 PNG_HANDLE_CHUNK_NEVER 1
1115 PNG_HANDLE_CHUNK_IF_SAFE 2
1116 PNG_HANDLE_CHUNK_ALWAYS 3
1117 chunk_list - list of chunks affected (a byte string,
1118 five bytes per chunk, NULL or '\0' if
1120 num_chunks - number of chunks affected; if 0, all
1121 unknown chunks are affected. If nonzero,
1122 only the chunks in the list are affected
1124 Unknown chunks declared in this way will be saved as raw data onto a
1125 list of png_unknown_chunk structures. If a chunk that is normally
1126 known to libpng is named in the list, it will be handled as unknown,
1127 according to the "keep" directive. If a chunk is named in successive
1128 instances of png_set_keep_unknown_chunks(), the final instance will
1129 take precedence. The IHDR and IEND chunks should not be named in
1130 chunk_list; if they are, libpng will process them normally anyway.
1132 .SS The high-level read interface
1134 At this point there are two ways to proceed; through the high-level
1135 read interface, or through a sequence of low-level read operations.
1136 You can use the high-level interface if (a) you are willing to read
1137 the entire image into memory, and (b) the input transformations
1138 you want to do are limited to the following set:
1140 PNG_TRANSFORM_IDENTITY No transformation
1141 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1143 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1144 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1146 PNG_TRANSFORM_PACKSWAP Change order of packed
1148 PNG_TRANSFORM_EXPAND Perform set_expand()
1149 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1150 PNG_TRANSFORM_SHIFT Normalize pixels to the
1152 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1154 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1156 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1158 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1160 (This excludes setting a background color, doing gamma transformation,
1161 dithering, and setting filler.) If this is the case, simply do this:
1163 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1165 where png_transforms is an integer containing the logical OR of
1166 some set of transformation flags. This call is equivalent to png_read_info(),
1167 followed the set of transformations indicated by the transform mask,
1168 then png_read_image(), and finally png_read_end().
1170 (The final parameter of this call is not yet used. Someday it might point
1171 to transformation parameters required by some future input transform.)
1173 After you have called png_read_png(), you can retrieve the image data
1176 row_pointers = png_get_rows(png_ptr, info_ptr);
1178 where row_pointers is an array of pointers to the pixel data for each row:
1180 png_bytep row_pointers[height];
1182 If you know your image size and pixel size ahead of time, you can allocate
1183 row_pointers prior to calling png_read_png() with
1185 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1187 "Image is too tall to process in memory");
1188 if (width > PNG_UINT_32_MAX/pixel_size)
1190 "Image is too wide to process in memory");
1191 row_pointers = png_malloc(png_ptr,
1192 height*png_sizeof(png_bytep));
1193 for (int i=0; i<height, i++)
1194 row_pointers[i]=png_malloc(png_ptr,
1196 png_set_rows(png_ptr, info_ptr, &row_pointers);
1198 Alternatively you could allocate your image in one big block and define
1199 row_pointers[i] to point into the proper places in your block.
1201 If you use png_set_rows(), the application is responsible for freeing
1202 row_pointers (and row_pointers[i], if they were separately allocated).
1204 If you don't allocate row_pointers ahead of time, png_read_png() will
1205 do it, and it'll be free'ed when you call png_destroy_*().
1207 .SS The low-level read interface
1209 If you are going the low-level route, you are now ready to read all
1210 the file information up to the actual image data. You do this with a
1211 call to png_read_info().
1213 png_read_info(png_ptr, info_ptr);
1215 This will process all chunks up to but not including the image data.
1217 .SS Querying the info structure
1219 Functions are used to get the information from the info_ptr once it
1220 has been read. Note that these fields may not be completely filled
1221 in until png_read_end() has read the chunk data following the image.
1223 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1224 &bit_depth, &color_type, &interlace_type,
1225 &compression_type, &filter_method);
1227 width - holds the width of the image
1228 in pixels (up to 2^31).
1229 height - holds the height of the image
1230 in pixels (up to 2^31).
1231 bit_depth - holds the bit depth of one of the
1232 image channels. (valid values are
1233 1, 2, 4, 8, 16 and depend also on
1234 the color_type. See also
1235 significant bits (sBIT) below).
1236 color_type - describes which color/alpha channels
1239 (bit depths 1, 2, 4, 8, 16)
1240 PNG_COLOR_TYPE_GRAY_ALPHA
1242 PNG_COLOR_TYPE_PALETTE
1243 (bit depths 1, 2, 4, 8)
1246 PNG_COLOR_TYPE_RGB_ALPHA
1249 PNG_COLOR_MASK_PALETTE
1250 PNG_COLOR_MASK_COLOR
1251 PNG_COLOR_MASK_ALPHA
1253 filter_method - (must be PNG_FILTER_TYPE_BASE
1254 for PNG 1.0, and can also be
1255 PNG_INTRAPIXEL_DIFFERENCING if
1256 the PNG datastream is embedded in
1257 a MNG-1.0 datastream)
1258 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1260 interlace_type - (PNG_INTERLACE_NONE or
1261 PNG_INTERLACE_ADAM7)
1262 Any or all of interlace_type, compression_type, of
1263 filter_method can be NULL if you are
1264 not interested in their values.
1266 channels = png_get_channels(png_ptr, info_ptr);
1267 channels - number of channels of info for the
1268 color type (valid values are 1 (GRAY,
1269 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1270 4 (RGB_ALPHA or RGB + filler byte))
1271 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1272 rowbytes - number of bytes needed to hold a row
1274 signature = png_get_signature(png_ptr, info_ptr);
1275 signature - holds the signature read from the
1276 file (if any). The data is kept in
1277 the same offset it would be if the
1278 whole signature were read (i.e. if an
1279 application had already read in 4
1280 bytes of signature before starting
1281 libpng, the remaining 4 bytes would
1282 be in signature[4] through signature[7]
1283 (see png_set_sig_bytes())).
1286 width = png_get_image_width(png_ptr,
1288 height = png_get_image_height(png_ptr,
1290 bit_depth = png_get_bit_depth(png_ptr,
1292 color_type = png_get_color_type(png_ptr,
1294 filter_method = png_get_filter_type(png_ptr,
1296 compression_type = png_get_compression_type(png_ptr,
1298 interlace_type = png_get_interlace_type(png_ptr,
1302 These are also important, but their validity depends on whether the chunk
1303 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1304 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1305 data has been read, or zero if it is missing. The parameters to the
1306 png_get_<chunk> are set directly if they are simple data types, or a pointer
1307 into the info_ptr is returned for any complex types.
1309 png_get_PLTE(png_ptr, info_ptr, &palette,
1311 palette - the palette for the file
1312 (array of png_color)
1313 num_palette - number of entries in the palette
1315 png_get_gAMA(png_ptr, info_ptr, &gamma);
1316 gamma - the gamma the file is written
1319 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1320 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1321 The presence of the sRGB chunk
1322 means that the pixel data is in the
1323 sRGB color space. This chunk also
1324 implies specific values of gAMA and
1327 png_get_iCCP(png_ptr, info_ptr, &name,
1328 &compression_type, &profile, &proflen);
1329 name - The profile name.
1330 compression - The compression type; always
1331 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1332 You may give NULL to this argument to
1334 profile - International Color Consortium color
1335 profile data. May contain NULs.
1336 proflen - length of profile data in bytes.
1338 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1339 sig_bit - the number of significant bits for
1340 (PNG_INFO_sBIT) each of the gray,
1341 red, green, and blue channels,
1342 whichever are appropriate for the
1343 given color type (png_color_16)
1345 png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
1347 trans - array of transparent entries for
1348 palette (PNG_INFO_tRNS)
1349 trans_values - graylevel or color sample values of
1350 the single transparent color for
1351 non-paletted images (PNG_INFO_tRNS)
1352 num_trans - number of transparent entries
1355 png_get_hIST(png_ptr, info_ptr, &hist);
1357 hist - histogram of palette (array of
1360 png_get_tIME(png_ptr, info_ptr, &mod_time);
1361 mod_time - time image was last modified
1364 png_get_bKGD(png_ptr, info_ptr, &background);
1365 background - background color (PNG_VALID_bKGD)
1366 valid 16-bit red, green and blue
1367 values, regardless of color_type
1369 num_comments = png_get_text(png_ptr, info_ptr,
1370 &text_ptr, &num_text);
1371 num_comments - number of comments
1372 text_ptr - array of png_text holding image
1374 text_ptr[i].compression - type of compression used
1375 on "text" PNG_TEXT_COMPRESSION_NONE
1376 PNG_TEXT_COMPRESSION_zTXt
1377 PNG_ITXT_COMPRESSION_NONE
1378 PNG_ITXT_COMPRESSION_zTXt
1379 text_ptr[i].key - keyword for comment. Must contain
1381 text_ptr[i].text - text comments for current
1382 keyword. Can be empty.
1383 text_ptr[i].text_length - length of text string,
1384 after decompression, 0 for iTXt
1385 text_ptr[i].itxt_length - length of itxt string,
1386 after decompression, 0 for tEXt/zTXt
1387 text_ptr[i].lang - language of comment (empty
1388 string for unknown).
1389 text_ptr[i].lang_key - keyword in UTF-8
1390 (empty string for unknown).
1391 num_text - number of comments (same as
1392 num_comments; you can put NULL here
1393 to avoid the duplication)
1394 Note while png_set_text() will accept text, language,
1395 and translated keywords that can be NULL pointers, the
1396 structure returned by png_get_text will always contain
1397 regular zero-terminated C strings. They might be
1398 empty strings but they will never be NULL pointers.
1400 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1402 palette_ptr - array of palette structures holding
1403 contents of one or more sPLT chunks
1405 num_spalettes - number of sPLT chunks read.
1407 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1409 offset_x - positive offset from the left edge
1411 offset_y - positive offset from the top edge
1413 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1415 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1417 res_x - pixels/unit physical resolution in
1419 res_y - pixels/unit physical resolution in
1421 unit_type - PNG_RESOLUTION_UNKNOWN,
1422 PNG_RESOLUTION_METER
1424 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1426 unit - physical scale units (an integer)
1427 width - width of a pixel in physical scale units
1428 height - height of a pixel in physical scale units
1429 (width and height are doubles)
1431 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1433 unit - physical scale units (an integer)
1434 width - width of a pixel in physical scale units
1435 height - height of a pixel in physical scale units
1436 (width and height are strings like "2.54")
1438 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1439 info_ptr, &unknowns)
1440 unknowns - array of png_unknown_chunk
1441 structures holding unknown chunks
1442 unknowns[i].name - name of unknown chunk
1443 unknowns[i].data - data of unknown chunk
1444 unknowns[i].size - size of unknown chunk's data
1445 unknowns[i].location - position of chunk in file
1447 The value of "i" corresponds to the order in which the
1448 chunks were read from the PNG file or inserted with the
1449 png_set_unknown_chunks() function.
1451 The data from the pHYs chunk can be retrieved in several convenient
1454 res_x = png_get_x_pixels_per_meter(png_ptr,
1456 res_y = png_get_y_pixels_per_meter(png_ptr,
1458 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1460 res_x = png_get_x_pixels_per_inch(png_ptr,
1462 res_y = png_get_y_pixels_per_inch(png_ptr,
1464 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1466 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1469 (Each of these returns 0 [signifying "unknown"] if
1470 the data is not present or if res_x is 0;
1471 res_x_and_y is 0 if res_x != res_y)
1473 The data from the oFFs chunk can be retrieved in several convenient
1476 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1477 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1478 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1479 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1481 (Each of these returns 0 [signifying "unknown" if both
1482 x and y are 0] if the data is not present or if the
1483 chunk is present but the unit is the pixel)
1485 For more information, see the png_info definition in png.h and the
1486 PNG specification for chunk contents. Be careful with trusting
1487 rowbytes, as some of the transformations could increase the space
1488 needed to hold a row (expand, filler, gray_to_rgb, etc.).
1489 See png_read_update_info(), below.
1491 A quick word about text_ptr and num_text. PNG stores comments in
1492 keyword/text pairs, one pair per chunk, with no limit on the number
1493 of text chunks, and a 2^31 byte limit on their size. While there are
1494 suggested keywords, there is no requirement to restrict the use to these
1495 strings. It is strongly suggested that keywords and text be sensible
1496 to humans (that's the point), so don't use abbreviations. Non-printing
1497 symbols are not allowed. See the PNG specification for more details.
1498 There is also no requirement to have text after the keyword.
1500 Keywords should be limited to 79 Latin-1 characters without leading or
1501 trailing spaces, but non-consecutive spaces are allowed within the
1502 keyword. It is possible to have the same keyword any number of times.
1503 The text_ptr is an array of png_text structures, each holding a
1504 pointer to a language string, a pointer to a keyword and a pointer to
1505 a text string. The text string, language code, and translated
1506 keyword may be empty or NULL pointers. The keyword/text
1507 pairs are put into the array in the order that they are received.
1508 However, some or all of the text chunks may be after the image, so, to
1509 make sure you have read all the text chunks, don't mess with these
1510 until after you read the stuff after the image. This will be
1511 mentioned again below in the discussion that goes with png_read_end().
1513 .SS Input transformations
1515 After you've read the header information, you can set up the library
1516 to handle any special transformations of the image data. The various
1517 ways to transform the data will be described in the order that they
1518 should occur. This is important, as some of these change the color
1519 type and/or bit depth of the data, and some others only work on
1520 certain color types and bit depths. Even though each transformation
1521 checks to see if it has data that it can do something with, you should
1522 make sure to only enable a transformation if it will be valid for the
1523 data. For example, don't swap red and blue on grayscale data.
1525 The colors used for the background and transparency values should be
1526 supplied in the same format/depth as the current image data. They
1527 are stored in the same format/depth as the image data in a bKGD or tRNS
1528 chunk, so this is what libpng expects for this data. The colors are
1529 transformed to keep in sync with the image data when an application
1530 calls the png_read_update_info() routine (see below).
1532 Data will be decoded into the supplied row buffers packed into bytes
1533 unless the library has been told to transform it into another format.
1534 For example, 4 bit/pixel paletted or grayscale data will be returned
1535 2 pixels/byte with the leftmost pixel in the high-order bits of the
1536 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1537 in RGB RGB RGB format unless png_set_filler() is called to insert filler
1538 bytes, either before or after each RGB triplet. 16-bit RGB data will
1539 be returned RRGGBB RRGGBB, with the most significant byte of the color
1540 value first, unless png_set_strip_16() is called to transform it to
1541 regular RGB RGB triplets, or png_set_filler() is called to insert
1542 filler bytes, either before or after each RRGGBB triplet. Similarly,
1543 8-bit or 16-bit grayscale data can be modified with png_set_filler()
1544 or png_set_strip_16().
1546 The following code transforms grayscale images of less than 8 to 8 bits,
1547 changes paletted images to RGB, and adds a full alpha channel if there is
1548 transparency information in a tRNS chunk. This is most useful on
1549 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1550 viewing application that wishes to treat all images in the same way.
1552 if (color_type == PNG_COLOR_TYPE_PALETTE)
1553 png_set_palette_to_rgb(png_ptr);
1555 if (color_type == PNG_COLOR_TYPE_GRAY &&
1556 bit_depth < 8) png_set_gray_1_2_4_to_8(png_ptr);
1558 if (png_get_valid(png_ptr, info_ptr,
1559 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1561 These three functions are actually aliases for png_set_expand(), added
1562 in libpng version 1.0.4, with the function names expanded to improve code
1563 readability. In some future version they may actually do different
1566 PNG can have files with 16 bits per channel. If you only can handle
1567 8 bits per channel, this will strip the pixels down to 8 bit.
1569 if (bit_depth == 16)
1570 png_set_strip_16(png_ptr);
1572 If, for some reason, you don't need the alpha channel on an image,
1573 and you want to remove it rather than combining it with the background
1574 (but the image author certainly had in mind that you *would* combine
1575 it with the background, so that's what you should probably do):
1577 if (color_type & PNG_COLOR_MASK_ALPHA)
1578 png_set_strip_alpha(png_ptr);
1580 In PNG files, the alpha channel in an image
1581 is the level of opacity. If you need the alpha channel in an image to
1582 be the level of transparency instead of opacity, you can invert the
1583 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1584 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1585 images) is fully transparent, with
1587 png_set_invert_alpha(png_ptr);
1589 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1590 they can, resulting in, for example, 8 pixels per byte for 1 bit
1591 files. This code expands to 1 pixel per byte without changing the
1592 values of the pixels:
1595 png_set_packing(png_ptr);
1597 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1598 stored in a PNG image have been "scaled" or "shifted" up to the next
1599 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
1600 8 bits/sample in the range [0, 255]). However, it is also possible to
1601 convert the PNG pixel data back to the original bit depth of the image.
1602 This call reduces the pixels back down to the original bit depth:
1604 png_color_8p sig_bit;
1606 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1607 png_set_shift(png_ptr, sig_bit);
1609 PNG files store 3-color pixels in red, green, blue order. This code
1610 changes the storage of the pixels to blue, green, red:
1612 if (color_type == PNG_COLOR_TYPE_RGB ||
1613 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1614 png_set_bgr(png_ptr);
1616 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1617 into 4 or 8 bytes for windowing systems that need them in this format:
1619 if (color_type == PNG_COLOR_TYPE_RGB)
1620 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1622 where "filler" is the 8 or 16-bit number to fill with, and the location is
1623 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1624 you want the filler before the RGB or after. This transformation
1625 does not affect images that already have full alpha channels. To add an
1626 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1627 will generate RGBA pixels.
1629 If you are reading an image with an alpha channel, and you need the
1630 data as ARGB instead of the normal PNG format RGBA:
1632 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1633 png_set_swap_alpha(png_ptr);
1635 For some uses, you may want a grayscale image to be represented as
1636 RGB. This code will do that conversion:
1638 if (color_type == PNG_COLOR_TYPE_GRAY ||
1639 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1640 png_set_gray_to_rgb(png_ptr);
1642 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1645 if (color_type == PNG_COLOR_TYPE_RGB ||
1646 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1647 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1648 int red_weight, int green_weight);
1650 error_action = 1: silently do the conversion
1651 error_action = 2: issue a warning if the original
1652 image has any pixel where
1653 red != green or red != blue
1654 error_action = 3: issue an error and abort the
1655 conversion if the original
1656 image has any pixel where
1657 red != green or red != blue
1659 red_weight: weight of red component times 100000
1660 green_weight: weight of green component times 100000
1661 If either weight is negative, default
1662 weights (21268, 71514) are used.
1664 If you have set error_action = 1 or 2, you can
1665 later check whether the image really was gray, after processing
1666 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1667 It will return a png_byte that is zero if the image was gray or
1668 1 if there were any non-gray pixels. bKGD and sBIT data
1669 will be silently converted to grayscale, using the green channel
1670 data, regardless of the error_action setting.
1672 With red_weight+green_weight<=100000,
1673 the normalized graylevel is computed:
1675 int rw = red_weight * 65536;
1676 int gw = green_weight * 65536;
1677 int bw = 65536 - (rw + gw);
1678 gray = (rw*red + gw*green + bw*blue)/65536;
1680 The default values approximate those recommended in the Charles
1681 Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1682 Copyright (c) 1998-01-04 Charles Poynton poynton@inforamp.net
1684 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1686 Libpng approximates this with
1688 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1690 which can be expressed with integers as
1692 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1694 The calculation is done in a linear colorspace, if the image gamma
1697 If you have a grayscale and you are using png_set_expand_depth(),
1698 png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1699 a higher bit-depth, you must either supply the background color as a gray
1700 value at the original file bit-depth (need_expand = 1) or else supply the
1701 background color as an RGB triplet at the final, expanded bit depth
1702 (need_expand = 0). Similarly, if you are reading a paletted image, you
1703 must either supply the background color as a palette index (need_expand = 1)
1704 or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1706 png_color_16 my_background;
1707 png_color_16p image_background;
1709 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1710 png_set_background(png_ptr, image_background,
1711 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1713 png_set_background(png_ptr, &my_background,
1714 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1716 The png_set_background() function tells libpng to composite images
1717 with alpha or simple transparency against the supplied background
1718 color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1719 you may use this color, or supply another color more suitable for
1720 the current display (e.g., the background color from a web page). You
1721 need to tell libpng whether the color is in the gamma space of the
1722 display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1723 (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1724 that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1725 know why anyone would use this, but it's here).
1727 To properly display PNG images on any kind of system, the application needs
1728 to know what the display gamma is. Ideally, the user will know this, and
1729 the application will allow them to set it. One method of allowing the user
1730 to set the display gamma separately for each system is to check for a
1731 SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1734 Note that display_gamma is the overall gamma correction required to produce
1735 pleasing results, which depends on the lighting conditions in the surrounding
1736 environment. In a dim or brightly lit room, no compensation other than
1737 the physical gamma exponent of the monitor is needed, while in a dark room
1738 a slightly smaller exponent is better.
1740 double gamma, screen_gamma;
1742 if (/* We have a user-defined screen
1745 screen_gamma = user_defined_screen_gamma;
1747 /* One way that applications can share the same
1748 screen gamma value */
1749 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1752 screen_gamma = (double)atof(gamma_str);
1754 /* If we don't have another value */
1757 screen_gamma = 2.2; /* A good guess for a
1758 PC monitor in a bright office or a dim room */
1759 screen_gamma = 2.0; /* A good guess for a
1760 PC monitor in a dark room */
1761 screen_gamma = 1.7 or 1.0; /* A good
1762 guess for Mac systems */
1765 The png_set_gamma() function handles gamma transformations of the data.
1766 Pass both the file gamma and the current screen_gamma. If the file does
1767 not have a gamma value, you can pass one anyway if you have an idea what
1768 it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1769 that file gammas are inverted from screen gammas. See the discussions
1770 on gamma in the PNG specification for an excellent description of what
1771 gamma is, and why all applications should support it. It is strongly
1772 recommended that PNG viewers support gamma correction.
1774 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1775 png_set_gamma(png_ptr, screen_gamma, gamma);
1777 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1779 If you need to reduce an RGB file to a paletted file, or if a paletted
1780 file has more entries then will fit on your screen, png_set_dither()
1781 will do that. Note that this is a simple match dither that merely
1782 finds the closest color available. This should work fairly well with
1783 optimized palettes, and fairly badly with linear color cubes. If you
1784 pass a palette that is larger then maximum_colors, the file will
1785 reduce the number of colors in the palette so it will fit into
1786 maximum_colors. If there is a histogram, it will use it to make
1787 more intelligent choices when reducing the palette. If there is no
1788 histogram, it may not do as good a job.
1790 if (color_type & PNG_COLOR_MASK_COLOR)
1792 if (png_get_valid(png_ptr, info_ptr,
1795 png_uint_16p histogram = NULL;
1797 png_get_hIST(png_ptr, info_ptr,
1799 png_set_dither(png_ptr, palette, num_palette,
1800 max_screen_colors, histogram, 1);
1804 png_color std_color_cube[MAX_SCREEN_COLORS] =
1807 png_set_dither(png_ptr, std_color_cube,
1808 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1813 PNG files describe monochrome as black being zero and white being one.
1814 The following code will reverse this (make black be one and white be
1817 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1818 png_set_invert_mono(png_ptr);
1820 This function can also be used to invert grayscale and gray-alpha images:
1822 if (color_type == PNG_COLOR_TYPE_GRAY ||
1823 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1824 png_set_invert_mono(png_ptr);
1826 PNG files store 16 bit pixels in network byte order (big-endian,
1827 ie. most significant bits first). This code changes the storage to the
1828 other way (little-endian, i.e. least significant bits first, the
1829 way PCs store them):
1831 if (bit_depth == 16)
1832 png_set_swap(png_ptr);
1834 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1835 need to change the order the pixels are packed into bytes, you can use:
1838 png_set_packswap(png_ptr);
1840 Finally, you can write your own transformation function if none of
1841 the existing ones meets your needs. This is done by setting a callback
1844 png_set_read_user_transform_fn(png_ptr,
1847 You must supply the function
1849 void read_transform_fn(png_ptr ptr, row_info_ptr
1850 row_info, png_bytep data)
1852 See pngtest.c for a working example. Your function will be called
1853 after all of the other transformations have been processed.
1855 You can also set up a pointer to a user structure for use by your
1856 callback function, and you can inform libpng that your transform
1857 function will change the number of channels or bit depth with the
1860 png_set_user_transform_info(png_ptr, user_ptr,
1861 user_depth, user_channels);
1863 The user's application, not libpng, is responsible for allocating and
1864 freeing any memory required for the user structure.
1866 You can retrieve the pointer via the function
1867 png_get_user_transform_ptr(). For example:
1869 voidp read_user_transform_ptr =
1870 png_get_user_transform_ptr(png_ptr);
1872 The last thing to handle is interlacing; this is covered in detail below,
1873 but you must call the function here if you want libpng to handle expansion
1874 of the interlaced image.
1876 number_of_passes = png_set_interlace_handling(png_ptr);
1878 After setting the transformations, libpng can update your png_info
1879 structure to reflect any transformations you've requested with this
1880 call. This is most useful to update the info structure's rowbytes
1881 field so you can use it to allocate your image memory. This function
1882 will also update your palette with the correct screen_gamma and
1883 background if these have been given with the calls above.
1885 png_read_update_info(png_ptr, info_ptr);
1887 After you call png_read_update_info(), you can allocate any
1888 memory you need to hold the image. The row data is simply
1889 raw byte data for all forms of images. As the actual allocation
1890 varies among applications, no example will be given. If you
1891 are allocating one large chunk, you will need to build an
1892 array of pointers to each row, as it will be needed for some
1893 of the functions below.
1895 .SS Reading image data
1897 After you've allocated memory, you can read the image data.
1898 The simplest way to do this is in one function call. If you are
1899 allocating enough memory to hold the whole image, you can just
1900 call png_read_image() and libpng will read in all the image data
1901 and put it in the memory area supplied. You will need to pass in
1902 an array of pointers to each row.
1904 This function automatically handles interlacing, so you don't need
1905 to call png_set_interlace_handling() or call this function multiple
1906 times, or any of that other stuff necessary with png_read_rows().
1908 png_read_image(png_ptr, row_pointers);
1910 where row_pointers is:
1912 png_bytep row_pointers[height];
1914 You can point to void or char or whatever you use for pixels.
1916 If you don't want to read in the whole image at once, you can
1917 use png_read_rows() instead. If there is no interlacing (check
1918 interlace_type == PNG_INTERLACE_NONE), this is simple:
1920 png_read_rows(png_ptr, row_pointers, NULL,
1923 where row_pointers is the same as in the png_read_image() call.
1925 If you are doing this just one row at a time, you can do this with
1926 a single row_pointer instead of an array of row_pointers:
1928 png_bytep row_pointer = row;
1929 png_read_row(png_ptr, row_pointer, NULL);
1931 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
1932 get somewhat harder. The only current (PNG Specification version 1.2)
1933 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
1934 is a somewhat complicated 2D interlace scheme, known as Adam7, that
1935 breaks down an image into seven smaller images of varying size, based
1938 libpng can fill out those images or it can give them to you "as is".
1939 If you want them filled out, there are two ways to do that. The one
1940 mentioned in the PNG specification is to expand each pixel to cover
1941 those pixels that have not been read yet (the "rectangle" method).
1942 This results in a blocky image for the first pass, which gradually
1943 smooths out as more pixels are read. The other method is the "sparkle"
1944 method, where pixels are drawn only in their final locations, with the
1945 rest of the image remaining whatever colors they were initialized to
1946 before the start of the read. The first method usually looks better,
1947 but tends to be slower, as there are more pixels to put in the rows.
1949 If you don't want libpng to handle the interlacing details, just call
1950 png_read_rows() seven times to read in all seven images. Each of the
1951 images is a valid image by itself, or they can all be combined on an
1952 8x8 grid to form a single image (although if you intend to combine them
1953 you would be far better off using the libpng interlace handling).
1955 The first pass will return an image 1/8 as wide as the entire image
1956 (every 8th column starting in column 0) and 1/8 as high as the original
1957 (every 8th row starting in row 0), the second will be 1/8 as wide
1958 (starting in column 4) and 1/8 as high (also starting in row 0). The
1959 third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
1960 1/8 as high (every 8th row starting in row 4), and the fourth pass will
1961 be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
1962 and every 4th row starting in row 0). The fifth pass will return an
1963 image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
1964 while the sixth pass will be 1/2 as wide and 1/2 as high as the original
1965 (starting in column 1 and row 0). The seventh and final pass will be as
1966 wide as the original, and 1/2 as high, containing all of the odd
1967 numbered scanlines. Phew!
1969 If you want libpng to expand the images, call this before calling
1970 png_start_read_image() or png_read_update_info():
1972 if (interlace_type == PNG_INTERLACE_ADAM7)
1974 = png_set_interlace_handling(png_ptr);
1976 This will return the number of passes needed. Currently, this
1977 is seven, but may change if another interlace type is added.
1978 This function can be called even if the file is not interlaced,
1979 where it will return one pass.
1981 If you are not going to display the image after each pass, but are
1982 going to wait until the entire image is read in, use the sparkle
1983 effect. This effect is faster and the end result of either method
1984 is exactly the same. If you are planning on displaying the image
1985 after each pass, the "rectangle" effect is generally considered the
1988 If you only want the "sparkle" effect, just call png_read_rows() as
1989 normal, with the third parameter NULL. Make sure you make pass over
1990 the image number_of_passes times, and you don't change the data in the
1991 rows between calls. You can change the locations of the data, just
1992 not the data. Each pass only writes the pixels appropriate for that
1993 pass, and assumes the data from previous passes is still valid.
1995 png_read_rows(png_ptr, row_pointers, NULL,
1998 If you only want the first effect (the rectangles), do the same as
1999 before except pass the row buffer in the third parameter, and leave
2000 the second parameter NULL.
2002 png_read_rows(png_ptr, NULL, row_pointers,
2005 .SS Finishing a sequential read
2007 After you are finished reading the image through either the high- or
2008 low-level interfaces, you can finish reading the file. If you are
2009 interested in comments or time, which may be stored either before or
2010 after the image data, you should pass the separate png_info struct if
2011 you want to keep the comments from before and after the image
2012 separate. If you are not interested, you can pass NULL.
2014 png_read_end(png_ptr, end_info);
2016 When you are done, you can free all memory allocated by libpng like this:
2018 png_destroy_read_struct(&png_ptr, &info_ptr,
2021 It is also possible to individually free the info_ptr members that
2022 point to libpng-allocated storage with the following function:
2024 png_free_data(png_ptr, info_ptr, mask, seq)
2025 mask - identifies data to be freed, a mask
2026 containing the logical OR of one or
2028 PNG_FREE_PLTE, PNG_FREE_TRNS,
2029 PNG_FREE_HIST, PNG_FREE_ICCP,
2030 PNG_FREE_PCAL, PNG_FREE_ROWS,
2031 PNG_FREE_SCAL, PNG_FREE_SPLT,
2032 PNG_FREE_TEXT, PNG_FREE_UNKN,
2033 or simply PNG_FREE_ALL
2034 seq - sequence number of item to be freed
2037 This function may be safely called when the relevant storage has
2038 already been freed, or has not yet been allocated, or was allocated
2039 by the user and not by libpng, and will in those
2040 cases do nothing. The "seq" parameter is ignored if only one item
2041 of the selected data type, such as PLTE, is allowed. If "seq" is not
2042 -1, and multiple items are allowed for the data type identified in
2043 the mask, such as text or sPLT, only the n'th item in the structure
2044 is freed, where n is "seq".
2046 The default behavior is only to free data that was allocated internally
2047 by libpng. This can be changed, so that libpng will not free the data,
2048 or so that it will free data that was allocated by the user with png_malloc()
2049 or png_zalloc() and passed in via a png_set_*() function, with
2051 png_data_freer(png_ptr, info_ptr, freer, mask)
2052 mask - which data elements are affected
2053 same choices as in png_free_data()
2055 PNG_DESTROY_WILL_FREE_DATA
2056 PNG_SET_WILL_FREE_DATA
2057 PNG_USER_WILL_FREE_DATA
2059 This function only affects data that has already been allocated.
2060 You can call this function after reading the PNG data but before calling
2061 any png_set_*() functions, to control whether the user or the png_set_*()
2062 function is responsible for freeing any existing data that might be present,
2063 and again after the png_set_*() functions to control whether the user
2064 or png_destroy_*() is supposed to free the data. When the user assumes
2065 responsibility for libpng-allocated data, the application must use
2066 png_free() to free it, and when the user transfers responsibility to libpng
2067 for data that the user has allocated, the user must have used png_malloc()
2068 or png_zalloc() to allocate it.
2070 If you allocated your row_pointers in a single block, as suggested above in
2071 the description of the high level read interface, you must not transfer
2072 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2073 because they would also try to free the individual row_pointers[i].
2075 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2076 separately, do not transfer responsibility for freeing text_ptr to libpng,
2077 because when libpng fills a png_text structure it combines these members with
2078 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2079 if you transfer responsibility for free'ing text_ptr from libpng to your
2080 application, your application must not separately free those members.
2082 The png_free_data() function will turn off the "valid" flag for anything
2083 it frees. If you need to turn the flag off for a chunk that was freed by your
2084 application instead of by libpng, you can use
2086 png_set_invalid(png_ptr, info_ptr, mask);
2087 mask - identifies the chunks to be made invalid,
2088 containing the logical OR of one or
2090 PNG_INFO_gAMA, PNG_INFO_sBIT,
2091 PNG_INFO_cHRM, PNG_INFO_PLTE,
2092 PNG_INFO_tRNS, PNG_INFO_bKGD,
2093 PNG_INFO_hIST, PNG_INFO_pHYs,
2094 PNG_INFO_oFFs, PNG_INFO_tIME,
2095 PNG_INFO_pCAL, PNG_INFO_sRGB,
2096 PNG_INFO_iCCP, PNG_INFO_sPLT,
2097 PNG_INFO_sCAL, PNG_INFO_IDAT
2099 For a more compact example of reading a PNG image, see the file example.c.
2101 .SS Reading PNG files progressively
2103 The progressive reader is slightly different then the non-progressive
2104 reader. Instead of calling png_read_info(), png_read_rows(), and
2105 png_read_end(), you make one call to png_process_data(), which calls
2106 callbacks when it has the info, a row, or the end of the image. You
2107 set up these callbacks with png_set_progressive_read_fn(). You don't
2108 have to worry about the input/output functions of libpng, as you are
2109 giving the library the data directly in png_process_data(). I will
2110 assume that you have read the section on reading PNG files above,
2111 so I will only highlight the differences (although I will show
2114 png_structp png_ptr;
2117 /* An example code fragment of how you would
2118 initialize the progressive reader in your
2121 initialize_png_reader()
2123 png_ptr = png_create_read_struct
2124 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2125 user_error_fn, user_warning_fn);
2128 info_ptr = png_create_info_struct(png_ptr);
2131 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2136 if (setjmp(png_jmpbuf(png_ptr)))
2138 png_destroy_read_struct(&png_ptr, &info_ptr,
2143 /* This one's new. You can provide functions
2144 to be called when the header info is valid,
2145 when each row is completed, and when the image
2146 is finished. If you aren't using all functions,
2147 you can specify NULL parameters. Even when all
2148 three functions are NULL, you need to call
2149 png_set_progressive_read_fn(). You can use
2150 any struct as the user_ptr (cast to a void pointer
2151 for the function call), and retrieve the pointer
2152 from inside the callbacks using the function
2154 png_get_progressive_ptr(png_ptr);
2156 which will return a void pointer, which you have
2157 to cast appropriately.
2159 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2160 info_callback, row_callback, end_callback);
2165 /* A code fragment that you call as you receive blocks
2168 process_data(png_bytep buffer, png_uint_32 length)
2170 if (setjmp(png_jmpbuf(png_ptr)))
2172 png_destroy_read_struct(&png_ptr, &info_ptr,
2177 /* This one's new also. Simply give it a chunk
2178 of data from the file stream (in order, of
2179 course). On machines with segmented memory
2180 models machines, don't give it any more than
2181 64K. The library seems to run fine with sizes
2182 of 4K. Although you can give it much less if
2183 necessary (I assume you can give it chunks of
2184 1 byte, I haven't tried less then 256 bytes
2185 yet). When this function returns, you may
2186 want to display any rows that were generated
2187 in the row callback if you don't already do
2190 png_process_data(png_ptr, info_ptr, buffer, length);
2194 /* This function is called (as set by
2195 png_set_progressive_read_fn() above) when enough data
2196 has been supplied so all of the header has been
2200 info_callback(png_structp png_ptr, png_infop info)
2202 /* Do any setup here, including setting any of
2203 the transformations mentioned in the Reading
2204 PNG files section. For now, you _must_ call
2205 either png_start_read_image() or
2206 png_read_update_info() after all the
2207 transformations are set (even if you don't set
2208 any). You may start getting rows before
2209 png_process_data() returns, so this is your
2210 last chance to prepare for that.
2214 /* This function is called when each row of image
2217 row_callback(png_structp png_ptr, png_bytep new_row,
2218 png_uint_32 row_num, int pass)
2220 /* If the image is interlaced, and you turned
2221 on the interlace handler, this function will
2222 be called for every row in every pass. Some
2223 of these rows will not be changed from the
2224 previous pass. When the row is not changed,
2225 the new_row variable will be NULL. The rows
2226 and passes are called in order, so you don't
2227 really need the row_num and pass, but I'm
2228 supplying them because it may make your life
2231 For the non-NULL rows of interlaced images,
2232 you must call png_progressive_combine_row()
2233 passing in the row and the old row. You can
2234 call this function for NULL rows (it will just
2235 return) and for non-interlaced images (it just
2236 does the memcpy for you) if it will make the
2237 code easier. Thus, you can just do this for
2241 png_progressive_combine_row(png_ptr, old_row,
2244 /* where old_row is what was displayed for
2245 previously for the row. Note that the first
2246 pass (pass == 0, really) will completely cover
2247 the old row, so the rows do not have to be
2248 initialized. After the first pass (and only
2249 for interlaced images), you will have to pass
2250 the current row, and the function will combine
2251 the old row and the new row.
2256 end_callback(png_structp png_ptr, png_infop info)
2258 /* This function is called after the whole image
2259 has been read, including any chunks after the
2260 image (up to and including the IEND). You
2261 will usually have the same info chunk as you
2262 had in the header, although some data may have
2263 been added to the comments and time fields.
2265 Most people won't do much here, perhaps setting
2266 a flag that marks the image as finished.
2274 Much of this is very similar to reading. However, everything of
2275 importance is repeated here, so you won't have to constantly look
2276 back up in the reading section to understand writing.
2280 You will want to do the I/O initialization before you get into libpng,
2281 so if it doesn't work, you don't have anything to undo. If you are not
2282 using the standard I/O functions, you will need to replace them with
2283 custom writing functions. See the discussion under Customizing libpng.
2285 FILE *fp = fopen(file_name, "wb");
2291 Next, png_struct and png_info need to be allocated and initialized.
2292 As these can be both relatively large, you may not want to store these
2293 on the stack, unless you have stack space to spare. Of course, you
2294 will want to check if they return NULL. If you are also reading,
2295 you won't want to name your read structure and your write structure
2296 both "png_ptr"; you can call them anything you like, such as
2297 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
2299 png_structp png_ptr = png_create_write_struct
2300 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2301 user_error_fn, user_warning_fn);
2305 png_infop info_ptr = png_create_info_struct(png_ptr);
2308 png_destroy_write_struct(&png_ptr,
2313 If you want to use your own memory allocation routines,
2314 define PNG_USER_MEM_SUPPORTED and use
2315 png_create_write_struct_2() instead of png_create_write_struct():
2317 png_structp png_ptr = png_create_write_struct_2
2318 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2319 user_error_fn, user_warning_fn, (png_voidp)
2320 user_mem_ptr, user_malloc_fn, user_free_fn);
2322 After you have these structures, you will need to set up the
2323 error handling. When libpng encounters an error, it expects to
2324 longjmp() back to your routine. Therefore, you will need to call
2325 setjmp() and pass the png_jmpbuf(png_ptr). If you
2326 write the file from different routines, you will need to update
2327 the png_jmpbuf(png_ptr) every time you enter a new routine that will
2328 call a png_*() function. See your documentation of setjmp/longjmp
2329 for your compiler for more information on setjmp/longjmp. See
2330 the discussion on libpng error handling in the Customizing Libpng
2331 section below for more information on the libpng error handling.
2333 if (setjmp(png_jmpbuf(png_ptr)))
2335 png_destroy_write_struct(&png_ptr, &info_ptr);
2342 If you would rather avoid the complexity of setjmp/longjmp issues,
2343 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2344 errors will result in a call to PNG_ABORT() which defaults to abort().
2346 Now you need to set up the output code. The default for libpng is to
2347 use the C function fwrite(). If you use this, you will need to pass a
2348 valid FILE * in the function png_init_io(). Be sure that the file is
2349 opened in binary mode. Again, if you wish to handle writing data in
2350 another way, see the discussion on libpng I/O handling in the Customizing
2351 Libpng section below.
2353 png_init_io(png_ptr, fp);
2357 At this point, you can set up a callback function that will be
2358 called after each row has been written, which you can use to control
2359 a progress meter or the like. It's demonstrated in pngtest.c.
2360 You must supply a function
2362 void write_row_callback(png_ptr, png_uint_32 row,
2365 /* put your code here */
2368 (You can give it another name that you like instead of "write_row_callback")
2370 To inform libpng about your function, use
2372 png_set_write_status_fn(png_ptr, write_row_callback);
2374 You now have the option of modifying how the compression library will
2375 run. The following functions are mainly for testing, but may be useful
2376 in some cases, like if you need to write PNG files extremely fast and
2377 are willing to give up some compression, or if you want to get the
2378 maximum possible compression at the expense of slower writing. If you
2379 have no special needs in this area, let the library do what it wants by
2380 not calling this function at all, as it has been tuned to deliver a good
2381 speed/compression ratio. The second parameter to png_set_filter() is
2382 the filter method, for which the only valid values are 0 (as of the
2383 July 1999 PNG specification, version 1.2) or 64 (if you are writing
2384 a PNG datastream that is to be embedded in a MNG datastream). The third
2385 parameter is a flag that indicates which filter type(s) are to be tested
2386 for each scanline. See the PNG specification for details on the specific filter
2390 /* turn on or off filtering, and/or choose
2391 specific filters. You can use either a single
2392 PNG_FILTER_VALUE_NAME or the logical OR of one
2393 or more PNG_FILTER_NAME masks. */
2394 png_set_filter(png_ptr, 0,
2395 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2396 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2397 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2398 PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2399 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2403 wants to start and stop using particular filters during compression,
2404 it should start out with all of the filters (to ensure that the previous
2405 row of pixels will be stored in case it's needed later), and then add
2406 and remove them after the start of compression.
2408 If you are writing a PNG datastream that is to be embedded in a MNG
2409 datastream, the second parameter can be either 0 or 64.
2411 The png_set_compression_*() functions interface to the zlib compression
2412 library, and should mostly be ignored unless you really know what you are
2413 doing. The only generally useful call is png_set_compression_level()
2414 which changes how much time zlib spends on trying to compress the image
2415 data. See the Compression Library (zlib.h and algorithm.txt, distributed
2416 with zlib) for details on the compression levels.
2418 /* set the zlib compression level */
2419 png_set_compression_level(png_ptr,
2420 Z_BEST_COMPRESSION);
2422 /* set other zlib parameters */
2423 png_set_compression_mem_level(png_ptr, 8);
2424 png_set_compression_strategy(png_ptr,
2425 Z_DEFAULT_STRATEGY);
2426 png_set_compression_window_bits(png_ptr, 15);
2427 png_set_compression_method(png_ptr, 8);
2428 png_set_compression_buffer_size(png_ptr, 8192)
2430 extern PNG_EXPORT(void,png_set_zbuf_size)
2432 .SS Setting the contents of info for output
2434 You now need to fill in the png_info structure with all the data you
2435 wish to write before the actual image. Note that the only thing you
2436 are allowed to write after the image is the text chunks and the time
2437 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2438 the latest PNG specification for more information on that. If you
2439 wish to write them before the image, fill them in now, and flag that
2440 data as being valid. If you want to wait until after the data, don't
2441 fill them until png_write_end(). For all the fields in png_info and
2442 their data types, see png.h. For explanations of what the fields
2443 contain, see the PNG specification.
2445 Some of the more important parts of the png_info are:
2447 png_set_IHDR(png_ptr, info_ptr, width, height,
2448 bit_depth, color_type, interlace_type,
2449 compression_type, filter_method)
2450 width - holds the width of the image
2451 in pixels (up to 2^31).
2452 height - holds the height of the image
2453 in pixels (up to 2^31).
2454 bit_depth - holds the bit depth of one of the
2456 (valid values are 1, 2, 4, 8, 16
2457 and depend also on the
2458 color_type. See also significant
2460 color_type - describes which color/alpha
2461 channels are present.
2463 (bit depths 1, 2, 4, 8, 16)
2464 PNG_COLOR_TYPE_GRAY_ALPHA
2466 PNG_COLOR_TYPE_PALETTE
2467 (bit depths 1, 2, 4, 8)
2470 PNG_COLOR_TYPE_RGB_ALPHA
2473 PNG_COLOR_MASK_PALETTE
2474 PNG_COLOR_MASK_COLOR
2475 PNG_COLOR_MASK_ALPHA
2477 interlace_type - PNG_INTERLACE_NONE or
2479 compression_type - (must be
2480 PNG_COMPRESSION_TYPE_DEFAULT)
2481 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2482 or, if you are writing a PNG to
2483 be embedded in a MNG datastream,
2485 PNG_INTRAPIXEL_DIFFERENCING)
2487 png_set_PLTE(png_ptr, info_ptr, palette,
2489 palette - the palette for the file
2490 (array of png_color)
2491 num_palette - number of entries in the palette
2493 png_set_gAMA(png_ptr, info_ptr, gamma);
2494 gamma - the gamma the image was created
2497 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2498 srgb_intent - the rendering intent
2499 (PNG_INFO_sRGB) The presence of
2500 the sRGB chunk means that the pixel
2501 data is in the sRGB color space.
2502 This chunk also implies specific
2503 values of gAMA and cHRM. Rendering
2504 intent is the CSS-1 property that
2505 has been defined by the International
2507 (http://www.color.org).
2509 PNG_sRGB_INTENT_SATURATION,
2510 PNG_sRGB_INTENT_PERCEPTUAL,
2511 PNG_sRGB_INTENT_ABSOLUTE, or
2512 PNG_sRGB_INTENT_RELATIVE.
2515 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2517 srgb_intent - the rendering intent
2518 (PNG_INFO_sRGB) The presence of the
2519 sRGB chunk means that the pixel
2520 data is in the sRGB color space.
2521 This function also causes gAMA and
2522 cHRM chunks with the specific values
2523 that are consistent with sRGB to be
2526 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2528 name - The profile name.
2529 compression - The compression type; always
2530 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2531 You may give NULL to this argument to
2533 profile - International Color Consortium color
2534 profile data. May contain NULs.
2535 proflen - length of profile data in bytes.
2537 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2538 sig_bit - the number of significant bits for
2539 (PNG_INFO_sBIT) each of the gray, red,
2540 green, and blue channels, whichever are
2541 appropriate for the given color type
2544 png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2546 trans - array of transparent entries for
2547 palette (PNG_INFO_tRNS)
2548 trans_values - graylevel or color sample values of
2549 the single transparent color for
2550 non-paletted images (PNG_INFO_tRNS)
2551 num_trans - number of transparent entries
2554 png_set_hIST(png_ptr, info_ptr, hist);
2556 hist - histogram of palette (array of
2559 png_set_tIME(png_ptr, info_ptr, mod_time);
2560 mod_time - time image was last modified
2563 png_set_bKGD(png_ptr, info_ptr, background);
2564 background - background color (PNG_VALID_bKGD)
2566 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2567 text_ptr - array of png_text holding image
2569 text_ptr[i].compression - type of compression used
2570 on "text" PNG_TEXT_COMPRESSION_NONE
2571 PNG_TEXT_COMPRESSION_zTXt
2572 PNG_ITXT_COMPRESSION_NONE
2573 PNG_ITXT_COMPRESSION_zTXt
2574 text_ptr[i].key - keyword for comment. Must contain
2576 text_ptr[i].text - text comments for current
2577 keyword. Can be NULL or empty.
2578 text_ptr[i].text_length - length of text string,
2579 after decompression, 0 for iTXt
2580 text_ptr[i].itxt_length - length of itxt string,
2581 after decompression, 0 for tEXt/zTXt
2582 text_ptr[i].lang - language of comment (NULL or
2584 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2585 or empty for unknown).
2586 num_text - number of comments
2588 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2590 palette_ptr - array of png_sPLT_struct structures
2591 to be added to the list of palettes
2592 in the info structure.
2593 num_spalettes - number of palette structures to be
2596 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2598 offset_x - positive offset from the left
2600 offset_y - positive offset from the top
2602 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2604 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2606 res_x - pixels/unit physical resolution
2608 res_y - pixels/unit physical resolution
2610 unit_type - PNG_RESOLUTION_UNKNOWN,
2611 PNG_RESOLUTION_METER
2613 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2614 unit - physical scale units (an integer)
2615 width - width of a pixel in physical scale units
2616 height - height of a pixel in physical scale units
2617 (width and height are doubles)
2619 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2620 unit - physical scale units (an integer)
2621 width - width of a pixel in physical scale units
2622 height - height of a pixel in physical scale units
2623 (width and height are strings like "2.54")
2625 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2627 unknowns - array of png_unknown_chunk
2628 structures holding unknown chunks
2629 unknowns[i].name - name of unknown chunk
2630 unknowns[i].data - data of unknown chunk
2631 unknowns[i].size - size of unknown chunk's data
2632 unknowns[i].location - position to write chunk in file
2633 0: do not write chunk
2634 PNG_HAVE_IHDR: before PLTE
2635 PNG_HAVE_PLTE: before IDAT
2636 PNG_AFTER_IDAT: after IDAT
2638 The "location" member is set automatically according to
2639 what part of the output file has already been written.
2640 You can change its value after calling png_set_unknown_chunks()
2641 as demonstrated in pngtest.c. Within each of the "locations",
2642 the chunks are sequenced according to their position in the
2643 structure (that is, the value of "i", which is the order in which
2644 the chunk was either read from the input file or defined with
2645 png_set_unknown_chunks).
2647 A quick word about text and num_text. text is an array of png_text
2648 structures. num_text is the number of valid structures in the array.
2649 Each png_text structure holds a language code, a keyword, a text value,
2650 and a compression type.
2652 The compression types have the same valid numbers as the compression
2653 types of the image data. Currently, the only valid number is zero.
2654 However, you can store text either compressed or uncompressed, unlike
2655 images, which always have to be compressed. So if you don't want the
2656 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2657 Because tEXt and zTXt chunks don't have a language field, if you
2658 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2659 any language code or translated keyword will not be written out.
2661 Until text gets around 1000 bytes, it is not worth compressing it.
2662 After the text has been written out to the file, the compression type
2663 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2664 so that it isn't written out again at the end (in case you are calling
2665 png_write_end() with the same struct.
2667 The keywords that are given in the PNG Specification are:
2669 Title Short (one line) title or
2671 Author Name of image's creator
2672 Description Description of image (possibly long)
2673 Copyright Copyright notice
2674 Creation Time Time of original image creation
2675 (usually RFC 1123 format, see below)
2676 Software Software used to create the image
2677 Disclaimer Legal disclaimer
2678 Warning Warning of nature of content
2679 Source Device used to create the image
2680 Comment Miscellaneous comment; conversion
2681 from other image format
2683 The keyword-text pairs work like this. Keywords should be short
2684 simple descriptions of what the comment is about. Some typical
2685 keywords are found in the PNG specification, as is some recommendations
2686 on keywords. You can repeat keywords in a file. You can even write
2687 some text before the image and some after. For example, you may want
2688 to put a description of the image before the image, but leave the
2689 disclaimer until after, so viewers working over modem connections
2690 don't have to wait for the disclaimer to go over the modem before
2691 they start seeing the image. Finally, keywords should be full
2692 words, not abbreviations. Keywords and text are in the ISO 8859-1
2693 (Latin-1) character set (a superset of regular ASCII) and can not
2694 contain NUL characters, and should not contain control or other
2695 unprintable characters. To make the comments widely readable, stick
2696 with basic ASCII, and avoid machine specific character set extensions
2697 like the IBM-PC character set. The keyword must be present, but
2698 you can leave off the text string on non-compressed pairs.
2699 Compressed pairs must have a text string, as only the text string
2700 is compressed anyway, so the compression would be meaningless.
2702 PNG supports modification time via the png_time structure. Two
2703 conversion routines are provided, png_convert_from_time_t() for
2704 time_t and png_convert_from_struct_tm() for struct tm. The
2705 time_t routine uses gmtime(). You don't have to use either of
2706 these, but if you wish to fill in the png_time structure directly,
2707 you should provide the time in universal time (GMT) if possible
2708 instead of your local time. Note that the year number is the full
2709 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2710 that months start with 1.
2712 If you want to store the time of the original image creation, you should
2713 use a plain tEXt chunk with the "Creation Time" keyword. This is
2714 necessary because the "creation time" of a PNG image is somewhat vague,
2715 depending on whether you mean the PNG file, the time the image was
2716 created in a non-PNG format, a still photo from which the image was
2717 scanned, or possibly the subject matter itself. In order to facilitate
2718 machine-readable dates, it is recommended that the "Creation Time"
2719 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2720 although this isn't a requirement. Unlike the tIME chunk, the
2721 "Creation Time" tEXt chunk is not expected to be automatically changed
2722 by the software. To facilitate the use of RFC 1123 dates, a function
2723 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2724 time to an RFC 1123 format string.
2726 .SS Writing unknown chunks
2728 You can use the png_set_unknown_chunks function to queue up chunks
2729 for writing. You give it a chunk name, raw data, and a size; that's
2730 all there is to it. The chunks will be written by the next following
2731 png_write_info_before_PLTE, png_write_info, or png_write_end function.
2732 Any chunks previously read into the info structure's unknown-chunk
2733 list will also be written out in a sequence that satisfies the PNG
2734 specification's ordering rules.
2736 .SS The high-level write interface
2738 At this point there are two ways to proceed; through the high-level
2739 write interface, or through a sequence of low-level write operations.
2740 You can use the high-level interface if your image data is present
2741 in the info structure. All defined output
2742 transformations are permitted, enabled by the following masks.
2744 PNG_TRANSFORM_IDENTITY No transformation
2745 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2746 PNG_TRANSFORM_PACKSWAP Change order of packed
2748 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2749 PNG_TRANSFORM_SHIFT Normalize pixels to the
2751 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2753 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2755 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2757 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2758 PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2760 If you have valid image data in the info structure (you can use
2761 png_set_rows() to put image data in the info structure), simply do this:
2763 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2765 where png_transforms is an integer containing the logical OR of some set of
2766 transformation flags. This call is equivalent to png_write_info(),
2767 followed the set of transformations indicated by the transform mask,
2768 then png_write_image(), and finally png_write_end().
2770 (The final parameter of this call is not yet used. Someday it might point
2771 to transformation parameters required by some future output transform.)
2773 .SS The low-level write interface
2775 If you are going the low-level route instead, you are now ready to
2776 write all the file information up to the actual image data. You do
2777 this with a call to png_write_info().
2779 png_write_info(png_ptr, info_ptr);
2781 Note that there is one transformation you may need to do before
2782 png_write_info(). In PNG files, the alpha channel in an image is the
2783 level of opacity. If your data is supplied as a level of
2784 transparency, you can invert the alpha channel before you write it, so
2785 that 0 is fully transparent and 255 (in 8-bit or paletted images) or
2786 65535 (in 16-bit images) is fully opaque, with
2788 png_set_invert_alpha(png_ptr);
2790 This must appear before png_write_info() instead of later with the
2791 other transformations because in the case of paletted images the tRNS
2792 chunk data has to be inverted before the tRNS chunk is written. If
2793 your image is not a paletted image, the tRNS data (which in such cases
2794 represents a single color to be rendered as transparent) won't need to
2795 be changed, and you can safely do this transformation after your
2796 png_write_info() call.
2798 If you need to write a private chunk that you want to appear before
2799 the PLTE chunk when PLTE is present, you can write the PNG info in
2800 two steps, and insert code to write your own chunk between them:
2802 png_write_info_before_PLTE(png_ptr, info_ptr);
2803 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2804 png_write_info(png_ptr, info_ptr);
2806 After you've written the file information, you can set up the library
2807 to handle any special transformations of the image data. The various
2808 ways to transform the data will be described in the order that they
2809 should occur. This is important, as some of these change the color
2810 type and/or bit depth of the data, and some others only work on
2811 certain color types and bit depths. Even though each transformation
2812 checks to see if it has data that it can do something with, you should
2813 make sure to only enable a transformation if it will be valid for the
2814 data. For example, don't swap red and blue on grayscale data.
2816 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2817 the library to strip input data that has 4 or 8 bytes per pixel down
2818 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2821 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2823 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2824 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2825 is stored XRGB or RGBX.
2827 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2828 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2829 If the data is supplied at 1 pixel per byte, use this code, which will
2830 correctly pack the pixels into a single byte:
2832 png_set_packing(png_ptr);
2834 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2835 data is of another bit depth, you can write an sBIT chunk into the
2836 file so that decoders can recover the original data if desired.
2838 /* Set the true bit depth of the image data */
2839 if (color_type & PNG_COLOR_MASK_COLOR)
2841 sig_bit.red = true_bit_depth;
2842 sig_bit.green = true_bit_depth;
2843 sig_bit.blue = true_bit_depth;
2847 sig_bit.gray = true_bit_depth;
2849 if (color_type & PNG_COLOR_MASK_ALPHA)
2851 sig_bit.alpha = true_bit_depth;
2854 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2856 If the data is stored in the row buffer in a bit depth other than
2857 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2858 this will scale the values to appear to be the correct bit depth as
2861 png_set_shift(png_ptr, &sig_bit);
2863 PNG files store 16 bit pixels in network byte order (big-endian,
2864 ie. most significant bits first). This code would be used if they are
2865 supplied the other way (little-endian, i.e. least significant bits
2866 first, the way PCs store them):
2869 png_set_swap(png_ptr);
2871 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2872 need to change the order the pixels are packed into bytes, you can use:
2875 png_set_packswap(png_ptr);
2877 PNG files store 3 color pixels in red, green, blue order. This code
2878 would be used if they are supplied as blue, green, red:
2880 png_set_bgr(png_ptr);
2882 PNG files describe monochrome as black being zero and white being
2883 one. This code would be used if the pixels are supplied with this reversed
2884 (black being one and white being zero):
2886 png_set_invert_mono(png_ptr);
2888 Finally, you can write your own transformation function if none of
2889 the existing ones meets your needs. This is done by setting a callback
2892 png_set_write_user_transform_fn(png_ptr,
2893 write_transform_fn);
2895 You must supply the function
2897 void write_transform_fn(png_ptr ptr, row_info_ptr
2898 row_info, png_bytep data)
2900 See pngtest.c for a working example. Your function will be called
2901 before any of the other transformations are processed.
2903 You can also set up a pointer to a user structure for use by your
2906 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
2908 The user_channels and user_depth parameters of this function are ignored
2909 when writing; you can set them to zero as shown.
2911 You can retrieve the pointer via the function png_get_user_transform_ptr().
2914 voidp write_user_transform_ptr =
2915 png_get_user_transform_ptr(png_ptr);
2917 It is possible to have libpng flush any pending output, either manually,
2918 or automatically after a certain number of lines have been written. To
2919 flush the output stream a single time call:
2921 png_write_flush(png_ptr);
2923 and to have libpng flush the output stream periodically after a certain
2924 number of scanlines have been written, call:
2926 png_set_flush(png_ptr, nrows);
2928 Note that the distance between rows is from the last time png_write_flush()
2929 was called, or the first row of the image if it has never been called.
2930 So if you write 50 lines, and then png_set_flush 25, it will flush the
2931 output on the next scanline, and every 25 lines thereafter, unless
2932 png_write_flush() is called before 25 more lines have been written.
2933 If nrows is too small (less than about 10 lines for a 640 pixel wide
2934 RGB image) the image compression may decrease noticeably (although this
2935 may be acceptable for real-time applications). Infrequent flushing will
2936 only degrade the compression performance by a few percent over images
2937 that do not use flushing.
2939 .SS Writing the image data
2941 That's it for the transformations. Now you can write the image data.
2942 The simplest way to do this is in one function call. If you have the
2943 whole image in memory, you can just call png_write_image() and libpng
2944 will write the image. You will need to pass in an array of pointers to
2945 each row. This function automatically handles interlacing, so you don't
2946 need to call png_set_interlace_handling() or call this function multiple
2947 times, or any of that other stuff necessary with png_write_rows().
2949 png_write_image(png_ptr, row_pointers);
2951 where row_pointers is:
2953 png_byte *row_pointers[height];
2955 You can point to void or char or whatever you use for pixels.
2957 If you don't want to write the whole image at once, you can
2958 use png_write_rows() instead. If the file is not interlaced,
2961 png_write_rows(png_ptr, row_pointers,
2964 row_pointers is the same as in the png_write_image() call.
2966 If you are just writing one row at a time, you can do this with
2967 a single row_pointer instead of an array of row_pointers:
2969 png_bytep row_pointer = row;
2971 png_write_row(png_ptr, row_pointer);
2973 When the file is interlaced, things can get a good deal more
2974 complicated. The only currently (as of the PNG Specification
2975 version 1.2, dated July 1999) defined interlacing scheme for PNG files
2976 is the "Adam7" interlace scheme, that breaks down an
2977 image into seven smaller images of varying size. libpng will build
2978 these images for you, or you can do them yourself. If you want to
2979 build them yourself, see the PNG specification for details of which
2980 pixels to write when.
2982 If you don't want libpng to handle the interlacing details, just
2983 use png_set_interlace_handling() and call png_write_rows() the
2984 correct number of times to write all seven sub-images.
2986 If you want libpng to build the sub-images, call this before you start
2990 png_set_interlace_handling(png_ptr);
2992 This will return the number of passes needed. Currently, this
2993 is seven, but may change if another interlace type is added.
2995 Then write the complete image number_of_passes times.
2997 png_write_rows(png_ptr, row_pointers,
3000 As some of these rows are not used, and thus return immediately,
3001 you may want to read about interlacing in the PNG specification,
3002 and only update the rows that are actually used.
3004 .SS Finishing a sequential write
3006 After you are finished writing the image, you should finish writing
3007 the file. If you are interested in writing comments or time, you should
3008 pass an appropriately filled png_info pointer. If you are not interested,
3011 png_write_end(png_ptr, info_ptr);
3013 When you are done, you can free all memory used by libpng like this:
3015 png_destroy_write_struct(&png_ptr, &info_ptr);
3017 It is also possible to individually free the info_ptr members that
3018 point to libpng-allocated storage with the following function:
3020 png_free_data(png_ptr, info_ptr, mask, seq)
3021 mask - identifies data to be freed, a mask
3022 containing the logical OR of one or
3024 PNG_FREE_PLTE, PNG_FREE_TRNS,
3025 PNG_FREE_HIST, PNG_FREE_ICCP,
3026 PNG_FREE_PCAL, PNG_FREE_ROWS,
3027 PNG_FREE_SCAL, PNG_FREE_SPLT,
3028 PNG_FREE_TEXT, PNG_FREE_UNKN,
3029 or simply PNG_FREE_ALL
3030 seq - sequence number of item to be freed
3033 This function may be safely called when the relevant storage has
3034 already been freed, or has not yet been allocated, or was allocated
3035 by the user and not by libpng, and will in those
3036 cases do nothing. The "seq" parameter is ignored if only one item
3037 of the selected data type, such as PLTE, is allowed. If "seq" is not
3038 -1, and multiple items are allowed for the data type identified in
3039 the mask, such as text or sPLT, only the n'th item in the structure
3040 is freed, where n is "seq".
3042 If you allocated data such as a palette that you passed
3043 in to libpng with png_set_*, you must not free it until just before the call to
3044 png_destroy_write_struct().
3046 The default behavior is only to free data that was allocated internally
3047 by libpng. This can be changed, so that libpng will not free the data,
3048 or so that it will free data that was allocated by the user with png_malloc()
3049 or png_zalloc() and passed in via a png_set_*() function, with
3051 png_data_freer(png_ptr, info_ptr, freer, mask)
3052 mask - which data elements are affected
3053 same choices as in png_free_data()
3055 PNG_DESTROY_WILL_FREE_DATA
3056 PNG_SET_WILL_FREE_DATA
3057 PNG_USER_WILL_FREE_DATA
3059 For example, to transfer responsibility for some data from a read structure
3060 to a write structure, you could use
3062 png_data_freer(read_ptr, read_info_ptr,
3063 PNG_USER_WILL_FREE_DATA,
3064 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3065 png_data_freer(write_ptr, write_info_ptr,
3066 PNG_DESTROY_WILL_FREE_DATA,
3067 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3069 thereby briefly reassigning responsibility for freeing to the user but
3070 immediately afterwards reassigning it once more to the write_destroy
3071 function. Having done this, it would then be safe to destroy the read
3072 structure and continue to use the PLTE, tRNS, and hIST data in the write
3075 This function only affects data that has already been allocated.
3076 You can call this function before calling after the png_set_*() functions
3077 to control whether the user or png_destroy_*() is supposed to free the data.
3078 When the user assumes responsibility for libpng-allocated data, the
3079 application must use
3080 png_free() to free it, and when the user transfers responsibility to libpng
3081 for data that the user has allocated, the user must have used png_malloc()
3082 or png_zalloc() to allocate it.
3084 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3085 separately, do not transfer responsibility for freeing text_ptr to libpng,
3086 because when libpng fills a png_text structure it combines these members with
3087 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3088 if you transfer responsibility for free'ing text_ptr from libpng to your
3089 application, your application must not separately free those members.
3090 For a more compact example of writing a PNG image, see the file example.c.
3092 .SH V. Modifying/Customizing libpng:
3094 There are three issues here. The first is changing how libpng does
3095 standard things like memory allocation, input/output, and error handling.
3096 The second deals with more complicated things like adding new chunks,
3097 adding new transformations, and generally changing how libpng works.
3098 Both of those are compile-time issues; that is, they are generally
3099 determined at the time the code is written, and there is rarely a need
3100 to provide the user with a means of changing them. The third is a
3101 run-time issue: choosing between and/or tuning one or more alternate
3102 versions of computationally intensive routines; specifically, optimized
3103 assembly-language (and therefore compiler- and platform-dependent)
3106 Memory allocation, input/output, and error handling
3108 All of the memory allocation, input/output, and error handling in libpng
3109 goes through callbacks that are user-settable. The default routines are
3110 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3111 these functions, call the appropriate png_set_*_fn() function.
3113 Memory allocation is done through the functions png_malloc()
3114 and png_free(). These currently just call the standard C functions. If
3115 your pointers can't access more then 64K at a time, you will want to set
3116 MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
3117 memory allocation on a platform will change between applications, these
3118 functions must be modified in the library at compile time. If you prefer
3119 to use a different method of allocating and freeing data, you can use
3120 png_create_read_struct_2() or png_create_write_struct_2() to register
3121 your own functions as described above.
3122 These functions also provide a void pointer that can be retrieved via
3124 mem_ptr=png_get_mem_ptr(png_ptr);
3126 Your replacement memory functions must have prototypes as follows:
3128 png_voidp malloc_fn(png_structp png_ptr,
3130 void free_fn(png_structp png_ptr, png_voidp ptr);
3132 Your malloc_fn() must return NULL in case of failure. The png_malloc()
3133 function will normally call png_error() if it receives a NULL from the
3134 system memory allocator or from your replacement malloc_fn().
3136 Input/Output in libpng is done through png_read() and png_write(),
3137 which currently just call fread() and fwrite(). The FILE * is stored in
3138 png_struct and is initialized via png_init_io(). If you wish to change
3139 the method of I/O, the library supplies callbacks that you can set
3140 through the function png_set_read_fn() and png_set_write_fn() at run
3141 time, instead of calling the png_init_io() function. These functions
3142 also provide a void pointer that can be retrieved via the function
3143 png_get_io_ptr(). For example:
3145 png_set_read_fn(png_structp read_ptr,
3146 voidp read_io_ptr, png_rw_ptr read_data_fn)
3148 png_set_write_fn(png_structp write_ptr,
3149 voidp write_io_ptr, png_rw_ptr write_data_fn,
3150 png_flush_ptr output_flush_fn);
3152 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3153 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3155 The replacement I/O functions must have prototypes as follows:
3157 void user_read_data(png_structp png_ptr,
3158 png_bytep data, png_size_t length);
3159 void user_write_data(png_structp png_ptr,
3160 png_bytep data, png_size_t length);
3161 void user_flush_data(png_structp png_ptr);
3163 Supplying NULL for the read, write, or flush functions sets them back
3164 to using the default C stream functions. It is an error to read from
3165 a write stream, and vice versa.
3167 Error handling in libpng is done through png_error() and png_warning().
3168 Errors handled through png_error() are fatal, meaning that png_error()
3169 should never return to its caller. Currently, this is handled via
3170 setjmp() and longjmp() (unless you have compiled libpng with
3171 PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3172 but you could change this to do things like exit() if you should wish.
3174 On non-fatal errors, png_warning() is called
3175 to print a warning message, and then control returns to the calling code.
3176 By default png_error() and png_warning() print a message on stderr via
3177 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3178 (because you don't want the messages) or PNG_NO_STDIO defined (because
3179 fprintf() isn't available). If you wish to change the behavior of the error
3180 functions, you will need to set up your own message callbacks. These
3181 functions are normally supplied at the time that the png_struct is created.
3182 It is also possible to redirect errors and warnings to your own replacement
3183 functions after png_create_*_struct() has been called by calling:
3185 png_set_error_fn(png_structp png_ptr,
3186 png_voidp error_ptr, png_error_ptr error_fn,
3187 png_error_ptr warning_fn);
3189 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3191 If NULL is supplied for either error_fn or warning_fn, then the libpng
3192 default function will be used, calling fprintf() and/or longjmp() if a
3193 problem is encountered. The replacement error functions should have
3194 parameters as follows:
3196 void user_error_fn(png_structp png_ptr,
3197 png_const_charp error_msg);
3198 void user_warning_fn(png_structp png_ptr,
3199 png_const_charp warning_msg);
3201 The motivation behind using setjmp() and longjmp() is the C++ throw and
3202 catch exception handling methods. This makes the code much easier to write,
3203 as there is no need to check every return code of every function call.
3204 However, there are some uncertainties about the status of local variables
3205 after a longjmp, so the user may want to be careful about doing anything after
3206 setjmp returns non-zero besides returning itself. Consult your compiler
3207 documentation for more details. For an alternative approach, you may wish
3208 to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3212 If you need to read or write custom chunks, you may need to get deeper
3213 into the libpng code. The library now has mechanisms for storing
3214 and writing chunks of unknown type; you can even declare callbacks
3215 for custom chunks. Hoewver, this may not be good enough if the
3216 library code itself needs to know about interactions between your
3217 chunk and existing `intrinsic' chunks.
3219 If you need to write a new intrinsic chunk, first read the PNG
3220 specification. Acquire a first level of
3221 understanding of how it works. Pay particular attention to the
3222 sections that describe chunk names, and look at how other chunks were
3223 designed, so you can do things similarly. Second, check out the
3224 sections of libpng that read and write chunks. Try to find a chunk
3225 that is similar to yours and use it as a template. More details can
3226 be found in the comments inside the code. It is best to handle unknown
3227 chunks in a generic method, via callback functions, instead of by
3228 modifying libpng functions.
3230 If you wish to write your own transformation for the data, look through
3231 the part of the code that does the transformations, and check out some of
3232 the simpler ones to get an idea of how they work. Try to find a similar
3233 transformation to the one you want to add and copy off of it. More details
3234 can be found in the comments inside the code itself.
3236 .SS Configuring for 16 bit platforms
3238 You will want to look into zconf.h to tell zlib (and thus libpng) that
3239 it cannot allocate more then 64K at a time. Even if you can, the memory
3240 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3242 .SS Configuring for DOS
3244 For DOS users who only have access to the lower 640K, you will
3245 have to limit zlib's memory usage via a png_set_compression_mem_level()
3246 call. See zlib.h or zconf.h in the zlib library for more information.
3248 .SS Configuring for Medium Model
3250 Libpng's support for medium model has been tested on most of the popular
3251 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3252 defined, and FAR gets defined to far in pngconf.h, and you should be
3253 all set. Everything in the library (except for zlib's structure) is
3254 expecting far data. You must use the typedefs with the p or pp on
3255 the end for pointers (or at least look at them and be careful). Make
3256 note that the rows of data are defined as png_bytepp, which is an
3257 unsigned char far * far *.
3259 .SS Configuring for gui/windowing platforms:
3261 You will need to write new error and warning functions that use the GUI
3262 interface, as described previously, and set them to be the error and
3263 warning functions at the time that png_create_*_struct() is called,
3264 in order to have them available during the structure initialization.
3265 They can be changed later via png_set_error_fn(). On some compilers,
3266 you may also have to change the memory allocators (png_malloc, etc.).
3268 .SS Configuring for compiler xxx:
3270 All includes for libpng are in pngconf.h. If you need to add/change/delete
3271 an include, this is the place to do it. The includes that are not
3272 needed outside libpng are protected by the PNG_INTERNAL definition,
3273 which is only defined for those routines inside libpng itself. The
3274 files in libpng proper only include png.h, which includes pngconf.h.
3276 .SS Configuring zlib:
3278 There are special functions to configure the compression. Perhaps the
3279 most useful one changes the compression level, which currently uses
3280 input compression values in the range 0 - 9. The library normally
3281 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3282 have shown that for a large majority of images, compression values in
3283 the range 3-6 compress nearly as well as higher levels, and do so much
3284 faster. For online applications it may be desirable to have maximum speed
3285 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3286 specify no compression (Z_NO_COMPRESSION = 0), but this would create
3287 files larger than just storing the raw bitmap. You can specify the
3288 compression level by calling:
3290 png_set_compression_level(png_ptr, level);
3292 Another useful one is to reduce the memory level used by the library.
3293 The memory level defaults to 8, but it can be lowered if you are
3294 short on memory (running DOS, for example, where you only have 640K).
3295 Note that the memory level does have an effect on compression; among
3296 other things, lower levels will result in sections of incompressible
3297 data being emitted in smaller stored blocks, with a correspondingly
3298 larger relative overhead of up to 15% in the worst case.
3300 png_set_compression_mem_level(png_ptr, level);
3302 The other functions are for configuring zlib. They are not recommended
3303 for normal use and may result in writing an invalid PNG file. See
3304 zlib.h for more information on what these mean.
3306 png_set_compression_strategy(png_ptr,
3308 png_set_compression_window_bits(png_ptr,
3310 png_set_compression_method(png_ptr, method);
3311 png_set_compression_buffer_size(png_ptr, size);
3313 .SS Controlling row filtering
3315 If you want to control whether libpng uses filtering or not, which
3316 filters are used, and how it goes about picking row filters, you
3317 can call one of these functions. The selection and configuration
3318 of row filters can have a significant impact on the size and
3319 encoding speed and a somewhat lesser impact on the decoding speed
3320 of an image. Filtering is enabled by default for RGB and grayscale
3321 images (with and without alpha), but not for paletted images nor
3322 for any images with bit depths less than 8 bits/pixel.
3324 The 'method' parameter sets the main filtering method, which is
3325 currently only '0' in the PNG 1.2 specification. The 'filters'
3326 parameter sets which filter(s), if any, should be used for each
3327 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3328 to turn filtering on and off, respectively.
3330 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3331 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3332 ORed together with '|' to specify one or more filters to use.
3333 These filters are described in more detail in the PNG specification.
3334 If you intend to change the filter type during the course of writing
3335 the image, you should start with flags set for all of the filters
3336 you intend to use so that libpng can initialize its internal
3337 structures appropriately for all of the filter types. (Note that this
3338 means the first row must always be adaptively filtered, because libpng
3339 currently does not allocate the filter buffers until png_write_row()
3340 is called for the first time.)
3342 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3343 PNG_FILTER_UP | PNG_FILTER_AVE |
3344 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3346 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3348 The second parameter can also be
3349 PNG_INTRAPIXEL_DIFFERENCING if you are
3350 writing a PNG to be embedded in a MNG
3351 datastream. This parameter must be the
3352 same as the value of filter_method used
3355 It is also possible to influence how libpng chooses from among the
3356 available filters. This is done in one or both of two ways - by
3357 telling it how important it is to keep the same filter for successive
3358 rows, and by telling it the relative computational costs of the filters.
3360 double weights[3] = {1.5, 1.3, 1.1},
3361 costs[PNG_FILTER_VALUE_LAST] =
3362 {1.0, 1.3, 1.3, 1.5, 1.7};
3364 png_set_filter_heuristics(png_ptr,
3365 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3368 The weights are multiplying factors that indicate to libpng that the
3369 row filter should be the same for successive rows unless another row filter
3370 is that many times better than the previous filter. In the above example,
3371 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3372 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
3373 and still be chosen, while the NONE filter could have a sum 1.1 times
3374 higher than other filters and still be chosen. Unspecified weights are
3375 taken to be 1.0, and the specified weights should probably be declining
3376 like those above in order to emphasize recent filters over older filters.
3378 The filter costs specify for each filter type a relative decoding cost
3379 to be considered when selecting row filters. This means that filters
3380 with higher costs are less likely to be chosen over filters with lower
3381 costs, unless their "sum of absolute differences" is that much smaller.
3382 The costs do not necessarily reflect the exact computational speeds of
3383 the various filters, since this would unduly influence the final image
3386 Note that the numbers above were invented purely for this example and
3387 are given only to help explain the function usage. Little testing has
3388 been done to find optimum values for either the costs or the weights.
3390 .SS Removing unwanted object code
3392 There are a bunch of #define's in pngconf.h that control what parts of
3393 libpng are compiled. All the defines end in _SUPPORTED. If you are
3394 never going to use a capability, you can change the #define to #undef
3395 before recompiling libpng and save yourself code and data space, or
3396 you can turn off individual capabilities with defines that begin with
3399 You can also turn all of the transforms and ancillary chunk capabilities
3400 off en masse with compiler directives that define
3401 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3403 along with directives to turn on any of the capabilities that you do
3404 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3405 the extra transformations but still leave the library fully capable of reading
3406 and writing PNG files with all known public chunks
3407 Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3408 produces a library that is incapable of reading or writing ancillary chunks.
3409 If you are not using the progressive reading capability, you can
3410 turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3411 this with the INTERLACING capability, which you'll still have).
3413 All the reading and writing specific code are in separate files, so the
3414 linker should only grab the files it needs. However, if you want to
3415 make sure, or if you are building a stand alone library, all the
3416 reading files start with pngr and all the writing files start with
3417 pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3418 are used for both reading and writing, and always need to be included.
3419 The progressive reader is in pngpread.c
3421 If you are creating or distributing a dynamically linked library (a .so
3422 or DLL file), you should not remove or disable any parts of the library,
3423 as this will cause applications linked with different versions of the
3424 library to fail if they call functions not available in your library.
3425 The size of the library itself should not be an issue, because only
3426 those sections that are actually used will be loaded into memory.
3428 .SS Requesting debug printout
3430 The macro definition PNG_DEBUG can be used to request debugging
3431 printout. Set it to an integer value in the range 0 to 3. Higher
3432 numbers result in increasing amounts of debugging information. The
3433 information is printed to the "stderr" file, unless another file
3434 name is specified in the PNG_DEBUG_FILE macro definition.
3436 When PNG_DEBUG > 0, the following functions (macros) become available:
3438 png_debug(level, message)
3439 png_debug1(level, message, p1)
3440 png_debug2(level, message, p1, p2)
3442 in which "level" is compared to PNG_DEBUG to decide whether to print
3443 the message, "message" is the formatted string to be printed,
3444 and p1 and p2 are parameters that are to be embedded in the string
3445 according to printf-style formatting directives. For example,
3447 png_debug1(2, "foo=%d\n", foo);
3452 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3454 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3455 can still use PNG_DEBUG to control your own debugging:
3461 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3462 having level = 0 will be printed. There aren't any such statements in
3463 this version of libpng, but if you insert some they will be printed.
3465 %-%.SH VI. Runtime optimization
3467 %-%A new feature in libpng 1.2.0 is the ability to dynamically switch between
3468 %-%standard and optimized versions of some routines. Currently these are
3469 %-%limited to three computationally intensive tasks when reading PNG files:
3470 %-%decoding row filters, expanding interlacing, and combining interlaced or
3471 %-%transparent row data with previous row data. Currently the optimized
3472 %-%versions are available only for x86 (Intel, AMD, etc.) platforms with
3473 %-%MMX support, though this may change in future versions. (For example,
3474 %-%the non-MMX assembler optimizations for zlib might become similarly
3475 %-%runtime-selectable in future releases, in which case libpng could be
3476 %-%extended to support them. Alternatively, the compile-time choice of
3477 %-%floating-point versus integer routines for gamma correction might become
3478 %-%runtime-selectable.)
3480 %-%Because such optimizations tend to be very platform- and compiler-dependent,
3481 %-%both in how they are written and in how they perform, the new runtime code
3482 %-%in libpng has been written to allow programs to query, enable, and disable
3483 %-%either specific optimizations or all such optimizations. For example, to
3484 %-%enable all possible optimizations (bearing in mind that some "optimizations"
3485 %-%may actually run more slowly in rare cases):
3487 %-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3488 %-% png_uint_32 mask, flags;
3490 %-% flags = png_get_asm_flags(png_ptr);
3491 %-% mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3492 %-% png_set_asm_flags(png_ptr, flags | mask);
3495 %-%To enable only optimizations relevant to reading PNGs, use PNG_SELECT_READ
3496 %-%by itself when calling png_get_asm_flagmask(); similarly for optimizing
3497 %-%only writing. To disable all optimizations:
3499 %-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3500 %-% flags = png_get_asm_flags(png_ptr);
3501 %-% mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3502 %-% png_set_asm_flags(png_ptr, flags & ~mask);
3505 %-%To enable or disable only MMX-related features, use png_get_mmx_flagmask()
3506 %-%in place of png_get_asm_flagmask(). The mmx version takes one additional
3509 %-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3510 %-% int selection = PNG_SELECT_READ | PNG_SELECT_WRITE;
3513 %-% mask = png_get_mmx_flagmask(selection, &compilerID);
3516 %-%On return, compilerID will indicate which version of the MMX assembler
3517 %-%optimizations was compiled. Currently two flavors exist: Microsoft
3518 %-%Visual C++ (compilerID == 1) and GNU C (a.k.a. gcc/gas, compilerID == 2).
3519 %-%On non-x86 platforms or on systems compiled without MMX optimizations, a
3520 %-%value of -1 is used.
3522 %-%Note that both png_get_asm_flagmask() and png_get_mmx_flagmask() return
3523 %-%all valid, settable optimization bits for the version of the library that's
3524 %-%currently in use. In the case of shared (dynamically linked) libraries,
3525 %-%this may include optimizations that did not exist at the time the code was
3526 %-%written and compiled. It is also possible, of course, to enable only known,
3527 %-%specific optimizations; for example:
3529 %-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3530 %-% flags = PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3531 %-% | PNG_ASM_FLAG_MMX_READ_INTERLACE \
3532 %-% | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3533 %-% | PNG_ASM_FLAG_MMX_READ_FILTER_UP \
3534 %-% | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3535 %-% | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH ;
3536 %-% png_set_asm_flags(png_ptr, flags);
3539 %-%This method would enable only the MMX read-optimizations available at the
3540 %-%time of libpng 1.2.0's release, regardless of whether a later version of
3541 %-%the DLL were actually being used. (Also note that these functions did not
3542 %-%exist in versions older than 1.2.0, so any attempt to run a dynamically
3543 %-%linked app on such an older version would fail.)
3545 %-%To determine whether the processor supports MMX instructions at all, use
3546 %-%the png_mmx_support() function:
3548 %-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3549 %-% mmxsupport = png_mmx_support();
3552 %-%It returns -1 if MMX support is not compiled into libpng, 0 if MMX code
3553 %-%is compiled but MMX is not supported by the processor, or 1 if MMX support
3554 %-%is fully available. Note that png_mmx_support(), png_get_mmx_flagmask(),
3555 %-%and png_get_asm_flagmask() all may be called without allocating and ini-
3556 %-%tializing any PNG structures (for example, as part of a usage screen or
3559 %-%The following code can be used to prevent an application from using the
3560 %-%thread_unsafe features, even if libpng was built with PNG_THREAD_UNSAFE_OK
3563 %-%#if defined(PNG_USE_PNGGCCRD) && defined(PNG_ASSEMBLER_CODE_SUPPORTED) \
3564 %-% && defined(PNG_THREAD_UNSAFE_OK)
3565 %-% /* Disable thread-unsafe features of pnggccrd */
3566 %-% if (png_access_version() >= 10200)
3568 %-% png_uint_32 mmx_disable_mask = 0;
3569 %-% png_uint_32 asm_flags;
3571 %-% mmx_disable_mask |= ( PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3572 %-% | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3573 %-% | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3574 %-% | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH );
3575 %-% asm_flags = png_get_asm_flags(png_ptr);
3576 %-% png_set_asm_flags(png_ptr, asm_flags & ~mmx_disable_mask);
3580 %-%For more extensive examples of runtime querying, enabling and disabling
3581 %-%of optimized features, see contrib/gregbook/readpng2.c in the libpng
3582 %-%source-code distribution.
3586 The MNG specification (available at http://www.libpng.org/pub/mng) allows
3587 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3588 Libpng can support some of these extensions. To enable them, use the
3589 png_permit_mng_features() function:
3591 feature_set = png_permit_mng_features(png_ptr, mask)
3592 mask is a png_uint_32 containing the logical OR of the
3593 features you want to enable. These include
3594 PNG_FLAG_MNG_EMPTY_PLTE
3595 PNG_FLAG_MNG_FILTER_64
3596 PNG_ALL_MNG_FEATURES
3597 feature_set is a png_uint_32 that is the logical AND of
3598 your mask with the set of MNG features that is
3599 supported by the version of libpng that you are using.
3601 It is an error to use this function when reading or writing a standalone
3602 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3603 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3604 and the MHDR and MEND chunks. Libpng does not provide support for these
3605 or any other MNG chunks; your application must provide its own support for
3606 them. You may wish to consider using libmng (available at
3607 http://www.libmng.com) instead.
3609 .SH VII. Changes to Libpng from version 0.88
3611 It should be noted that versions of libpng later than 0.96 are not
3612 distributed by the original libpng author, Guy Schalnat, nor by
3613 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3614 distributed versions 0.89 through 0.96, but rather by another member
3615 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3616 still alive and well, but they have moved on to other things.
3618 The old libpng functions png_read_init(), png_write_init(),
3619 png_info_init(), png_read_destroy(), and png_write_destroy() have been
3620 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3621 functions will be removed from libpng version 2.0.0.
3623 The preferred method of creating and initializing the libpng structures is
3624 via the png_create_read_struct(), png_create_write_struct(), and
3625 png_create_info_struct() because they isolate the size of the structures
3626 from the application, allow version error checking, and also allow the
3627 use of custom error handling routines during the initialization, which
3628 the old functions do not. The functions png_read_destroy() and
3629 png_write_destroy() do not actually free the memory that libpng
3630 allocated for these structs, but just reset the data structures, so they
3631 can be used instead of png_destroy_read_struct() and
3632 png_destroy_write_struct() if you feel there is too much system overhead
3633 allocating and freeing the png_struct for each image read.
3635 Setting the error callbacks via png_set_message_fn() before
3636 png_read_init() as was suggested in libpng-0.88 is no longer supported
3637 because this caused applications that do not use custom error functions
3638 to fail if the png_ptr was not initialized to zero. It is still possible
3639 to set the error callbacks AFTER png_read_init(), or to change them with
3640 png_set_error_fn(), which is essentially the same function, but with a new
3641 name to force compilation errors with applications that try to use the old
3644 Starting with version 1.0.7, you can find out which version of the library
3645 you are using at run-time:
3647 png_uint_32 libpng_vn = png_access_version_number();
3649 The number libpng_vn is constructed from the major version, minor
3650 version with leading zero, and release number with leading zero,
3651 (e.g., libpng_vn for version 1.0.7 is 10007).
3653 You can also check which version of png.h you used when compiling your
3656 png_uint_32 application_vn = PNG_LIBPNG_VER;
3658 .SH VII. Y2K Compliance in libpng
3662 Since the PNG Development group is an ad-hoc body, we can't make
3663 an official declaration.
3665 This is your unofficial assurance that libpng from version 0.71 and
3666 upward through 1.2.6 are Y2K compliant. It is my belief that earlier
3667 versions were also Y2K compliant.
3669 Libpng only has three year fields. One is a 2-byte unsigned integer that
3670 will hold years up to 65535. The other two hold the date in text
3671 format, and will hold years up to 9999.
3674 "png_uint_16 year" in png_time_struct.
3677 "png_charp time_buffer" in png_struct and
3678 "near_time_buffer", which is a local character string in png.c.
3680 There are seven time-related functions:
3682 png_convert_to_rfc_1123() in png.c
3683 (formerly png_convert_to_rfc_1152() in error)
3684 png_convert_from_struct_tm() in pngwrite.c, called
3686 png_convert_from_time_t() in pngwrite.c
3687 png_get_tIME() in pngget.c
3688 png_handle_tIME() in pngrutil.c, called in pngread.c
3689 png_set_tIME() in pngset.c
3690 png_write_tIME() in pngwutil.c, called in pngwrite.c
3692 All appear to handle dates properly in a Y2K environment. The
3693 png_convert_from_time_t() function calls gmtime() to convert from system
3694 clock time, which returns (year - 1900), which we properly convert to
3695 the full 4-digit year. There is a possibility that applications using
3696 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
3697 function, or that they are incorrectly passing only a 2-digit year
3698 instead of "year - 1900" into the png_convert_from_struct_tm() function,
3699 but this is not under our control. The libpng documentation has always
3700 stated that it works with 4-digit years, and the APIs have been
3703 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3704 integer to hold the year, and can hold years as large as 65535.
3706 zlib, upon which libpng depends, is also Y2K compliant. It contains
3707 no date-related code.
3710 Glenn Randers-Pehrson
3712 PNG Development Group
3716 Note about libpng version numbers:
3718 Due to various miscommunications, unforeseen code incompatibilities
3719 and occasional factors outside the authors' control, version numbering
3720 on the library has not always been consistent and straightforward.
3721 The following table summarizes matters since version 0.89c, which was
3722 the first widely used release:
3724 source png.h png.h shared-lib
3725 version string int version
3726 ------- ------ ----- ----------
3727 0.89c ("beta 3") 0.89 89 1.0.89
3728 0.90 ("beta 4") 0.90 90 0.90
3729 0.95 ("beta 5") 0.95 95 0.95
3730 0.96 ("beta 6") 0.96 96 0.96
3731 0.97b ("beta 7") 1.00.97 97 1.0.1
3732 0.97c 0.97 97 2.0.97
3735 0.99a-m 0.99 99 2.0.99
3737 1.0.0 1.0.0 100 2.1.0
3738 1.0.0 (from here on, the 100 2.1.0
3739 1.0.1 png.h string is 10001 2.1.0
3740 1.0.1a-e identical to the 10002 from here on, the
3741 1.0.2 source version) 10002 shared library is 2.V
3742 1.0.2a-b 10003 where V is the source
3743 1.0.1 10001 code version except as
3744 1.0.1a-e 10002 2.1.0.1a-e noted.
3746 1.0.2a-b 10003 2.1.0.2a-b
3748 1.0.3a-d 10004 2.1.0.3a-d
3750 1.0.4a-f 10005 2.1.0.4a-f
3751 1.0.5 (+ 2 patches) 10005 2.1.0.5
3752 1.0.5a-d 10006 2.1.0.5a-d
3753 1.0.5e-r 10100 2.1.0.5e-r
3754 1.0.5s-v 10006 2.1.0.5s-v
3755 1.0.6 (+ 3 patches) 10006 2.1.0.6
3756 1.0.6d-g 10007 2.1.0.6d-g
3759 1.0.6j 10007 2.1.0.6j
3760 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3761 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3762 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3763 1.0.7 1 10007 2.1.0.7
3764 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3765 1.0.8rc1 1 10008 2.1.0.8rc1
3766 1.0.8 1 10008 2.1.0.8
3767 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3768 1.0.9rc1 1 10009 2.1.0.9rc1
3769 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3770 1.0.9rc2 1 10009 2.1.0.9rc2
3771 1.0.9 1 10009 2.1.0.9
3772 1.0.10beta1 1 10010 2.1.0.10beta1
3773 1.0.10rc1 1 10010 2.1.0.10rc1
3774 1.0.10 1 10010 2.1.0.10
3775 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3776 1.0.11rc1 1 10011 2.1.0.11rc1
3777 1.0.11 1 10011 2.1.0.11
3778 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3779 1.0.12rc1 2 10012 2.1.0.12rc1
3780 1.0.12 2 10012 2.1.0.12
3781 1.1.0a-f - 10100 2.1.1.0a-f abandoned
3782 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3783 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
3784 1.2.0rc1 3 10200 3.1.2.0rc1
3785 1.2.0 3 10200 3.1.2.0
3786 1.2.1beta-4 3 10201 3.1.2.1beta1-4
3787 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
3788 1.2.1 3 10201 3.1.2.1
3789 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
3790 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
3791 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
3792 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
3793 1.0.13 10 10013 10.so.0.1.0.13
3794 1.2.2 12 10202 12.so.0.1.2.2
3795 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
3796 1.2.3 12 10203 12.so.0.1.2.3
3797 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
3798 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
3799 1.0.14 10 10014 10.so.0.1.0.14
3800 1.2.4 13 10204 12.so.0.1.2.4
3801 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
3802 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
3803 1.0.15 10 10015 10.so.0.1.0.15
3804 1.2.5 13 10205 12.so.0.1.2.5
3805 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
3806 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
3807 1.0.16 10 10016 10.so.0.1.0.16
3808 1.2.6 13 10206 12.so.0.1.2.6
3810 Henceforth the source version will match the shared-library minor
3811 and patch numbers; the shared-library major version number will be
3812 used for changes in backward compatibility, as it is intended. The
3813 PNG_PNGLIB_VER macro, which is not used within libpng but is available
3814 for applications, is an unsigned integer of the form xyyzz corresponding
3815 to the source version x.y.z (leading zeros in y and z). Beta versions
3816 were given the previous public release number plus a letter, until
3817 version 1.0.6j; from then on they were given the upcoming public
3818 release number plus "betaNN" or "rcN".
3825 ftp://ftp.uu.net/graphics/png
3826 http://www.libpng.org/pub/png
3831 (generally) at the same location as
3835 ftp://ftp.uu.net/pub/archiving/zip/zlib
3837 ftp://ftp.info-zip.org/pub/infozip/zlib
3840 .IR PNG specification: RFC 2083
3842 (generally) at the same location as
3846 ftp://ds.internic.net/rfc/rfc2083.txt
3848 or (as a W3C Recommendation) at
3850 http://www.w3.org/TR/REC-png.html
3853 In the case of any inconsistency between the PNG specification
3854 and this library, the specification takes precedence.
3857 This man page: Glenn Randers-Pehrson
3858 <glennrp@users.sourceforge.net>
3860 The contributing authors would like to thank all those who helped
3861 with testing, bug fixes, and patience. This wouldn't have been
3862 possible without all of you.
3864 Thanks to Frank J. T. Wojcik for helping with the documentation.
3866 Libpng version 1.2.6 - August 15, 2004:
3867 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
3868 Currently maintained by Glenn Randers-Pehrson (glennrp@users.sourceforge.net).
3870 Supported by the PNG development group
3872 (png-implement@ccrc.wustl.edu).
3874 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
3876 (This copy of the libpng notices is provided for your convenience. In case of
3877 any discrepancy between this copy and the notices in the file png.h that is
3878 included in the libpng distribution, the latter shall prevail.)
3880 If you modify libpng you may insert additional notices immediately following
3883 libpng version 1.2.6, August 15, 2004, is
3884 Copyright (c) 2004 Glenn Randers-Pehrson, and is
3885 distributed according to the same disclaimer and license as libpng-1.2.5
3886 with the following individual added to the list of Contributing Authors
3890 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
3891 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
3892 distributed according to the same disclaimer and license as libpng-1.0.6
3893 with the following individuals added to the list of Contributing Authors
3895 Simon-Pierre Cadieux
3899 and with the following additions to the disclaimer:
3901 There is no warranty against interference with your
3902 enjoyment of the library or against infringement.
3903 There is no warranty that our efforts or the library
3904 will fulfill any of your particular purposes or needs.
3905 This library is provided with all faults, and the entire
3906 risk of satisfactory quality, performance, accuracy, and
3907 effort is with the user.
3909 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
3910 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
3911 Distributed according to the same disclaimer and license as libpng-0.96,
3912 with the following individuals added to the list of Contributing Authors:
3915 Glenn Randers-Pehrson
3918 libpng versions 0.89, June 1996, through 0.96, May 1997, are
3919 Copyright (c) 1996, 1997 Andreas Dilger
3920 Distributed according to the same disclaimer and license as libpng-0.88,
3921 with the following individuals added to the list of Contributing Authors:
3930 libpng versions 0.5, May 1995, through 0.88, January 1996, are
3931 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
3933 For the purposes of this copyright and license, "Contributing Authors"
3934 is defined as the following set of individuals:
3942 The PNG Reference Library is supplied "AS IS". The Contributing Authors
3943 and Group 42, Inc. disclaim all warranties, expressed or implied,
3944 including, without limitation, the warranties of merchantability and of
3945 fitness for any purpose. The Contributing Authors and Group 42, Inc.
3946 assume no liability for direct, indirect, incidental, special, exemplary,
3947 or consequential damages, which may result from the use of the PNG
3948 Reference Library, even if advised of the possibility of such damage.
3950 Permission is hereby granted to use, copy, modify, and distribute this
3951 source code, or portions hereof, for any purpose, without fee, subject
3952 to the following restrictions:
3954 1. The origin of this source code must not be misrepresented.
3956 2. Altered versions must be plainly marked as such and
3957 must not be misrepresented as being the original source.
3959 3. This Copyright notice may not be removed or altered from
3960 any source or altered source distribution.
3962 The Contributing Authors and Group 42, Inc. specifically permit, without
3963 fee, and encourage the use of this source code as a component to
3964 supporting the PNG file format in commercial products. If you use this
3965 source code in a product, acknowledgment is not required but would be
3969 A "png_get_copyright" function is available, for convenient use in "about"
3972 printf("%s",png_get_copyright(NULL));
3974 Also, the PNG logo (in PNG format, of course) is supplied in the
3975 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
3977 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
3978 certification mark of the Open Source Initiative.
3980 Glenn Randers-Pehrson
3981 glennrp@users.sourceforge.net
projects / wxWidgets.git / blob