1README for libpng version 1.6.25 - September 1, 2016 (shared library 16.0) 2See the note about version numbers near the top of png.h 3 4See INSTALL for instructions on how to install libpng. 5 6Libpng comes in several distribution formats. Get libpng-*.tar.gz or 7libpng-*.tar.xz or if you want UNIX-style line endings in the text files, 8or lpng*.7z or lpng*.zip if you want DOS-style line endings. 9 10Version 0.89 was the first official release of libpng. Don't let the 11fact that it's the first release fool you. The libpng library has been in 12extensive use and testing since mid-1995. By late 1997 it had 13finally gotten to the stage where there hadn't been significant 14changes to the API in some time, and people have a bad feeling about 15libraries with versions < 1.0. Version 1.0.0 was released in 16March 1998. 17 18**** 19Note that some of the changes to the png_info structure render this 20version of the library binary incompatible with libpng-0.89 or 21earlier versions if you are using a shared library. The type of the 22"filler" parameter for png_set_filler() has changed from png_byte to 23png_uint_32, which will affect shared-library applications that use 24this function. 25 26To avoid problems with changes to the internals of png info_struct, 27new APIs have been made available in 0.95 to avoid direct application 28access to info_ptr. These functions are the png_set_<chunk> and 29png_get_<chunk> functions. These functions should be used when 30accessing/storing the info_struct data, rather than manipulating it 31directly, to avoid such problems in the future. 32 33It is important to note that the APIs did not make current programs 34that access the info struct directly incompatible with the new 35library, through libpng-1.2.x. In libpng-1.4.x, which was meant to 36be a transitional release, members of the png_struct and the 37info_struct can still be accessed, but the compiler will issue a 38warning about deprecated usage. Since libpng-1.5.0, direct access 39to these structs is not allowed, and the definitions of the structs 40reside in private pngstruct.h and pnginfo.h header files that are not 41accessible to applications. It is strongly suggested that new 42programs use the new APIs (as shown in example.c and pngtest.c), and 43older programs be converted to the new format, to facilitate upgrades 44in the future. 45**** 46 47Additions since 0.90 include the ability to compile libpng as a 48Windows DLL, and new APIs for accessing data in the info struct. 49Experimental functions include the ability to set weighting and cost 50factors for row filter selection, direct reads of integers from buffers 51on big-endian processors that support misaligned data access, faster 52methods of doing alpha composition, and more accurate 16->8 bit color 53conversion. 54 55The additions since 0.89 include the ability to read from a PNG stream 56which has had some (or all) of the signature bytes read by the calling 57application. This also allows the reading of embedded PNG streams that 58do not have the PNG file signature. As well, it is now possible to set 59the library action on the detection of chunk CRC errors. It is possible 60to set different actions based on whether the CRC error occurred in a 61critical or an ancillary chunk. 62 63The changes made to the library, and bugs fixed are based on discussions 64on the PNG-implement mailing list and not on material submitted 65privately to Guy, Andreas, or Glenn. They will forward any good 66suggestions to the list. 67 68For a detailed description on using libpng, read libpng-manual.txt. For 69examples of libpng in a program, see example.c and pngtest.c. For usage 70information and restrictions (what little they are) on libpng, see 71png.h. For a description on using zlib (the compression library used by 72libpng) and zlib's restrictions, see zlib.h 73 74I have included a general makefile, as well as several machine and 75compiler specific ones, but you may have to modify one for your own needs. 76 77You should use zlib 1.0.4 or later to run this, but it MAY work with 78versions as old as zlib 0.95. Even so, there are bugs in older zlib 79versions which can cause the output of invalid compression streams for 80some images. You will definitely need zlib 1.0.4 or later if you are 81taking advantage of the MS-DOS "far" structure allocation for the small 82and medium memory models. You should also note that zlib is a 83compression library that is useful for more things than just PNG files. 84You can use zlib as a drop-in replacement for fread() and fwrite() if 85you are so inclined. 86 87zlib should be available at the same place that libpng is, or at zlib.net. 88 89You may also want a copy of the PNG specification. It is available 90as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find 91these at http://www.libpng.org/pub/png/documents/ 92 93This code is currently being archived at libpng.sf.net in the 94[DOWNLOAD] area, and at ftp://ftp.simplesystems.org. If you can't find it 95in any of those places, e-mail me, and I'll help you find it. 96 97I am not a lawyer, but I believe that the Export Control Classification 98Number (ECCN) for libpng is EAR99, which means not subject to export 99controls or International Traffic in Arms Regulations (ITAR) because it 100is open source, publicly available software, that does not contain any 101encryption software. See the EAR, paragraphs 734.3(b)(3) and 734.7(b). 102 103If you have any code changes, requests, problems, etc., please e-mail 104them to me. Also, I'd appreciate any make files or project files, 105and any modifications you needed to make to get libpng to compile, 106along with a #define variable to tell what compiler/system you are on. 107If you needed to add transformations to libpng, or wish libpng would 108provide the image in a different way, drop me a note (and code, if 109possible), so I can consider supporting the transformation. 110Finally, if you get any warning messages when compiling libpng 111(note: not zlib), and they are easy to fix, I'd appreciate the 112fix. Please mention "libpng" somewhere in the subject line. Thanks. 113 114This release was created and will be supported by myself (of course 115based in a large way on Guy's and Andreas' earlier work), and the PNG 116development group. 117 118Send comments/corrections/commendations to png-mng-implement at 119lists.sourceforge.net (subscription required; visit 120https://lists.sourceforge.net/lists/listinfo/png-mng-implement 121to subscribe) or to glennrp at users.sourceforge.net 122 123You can't reach Guy, the original libpng author, at the addresses 124given in previous versions of this document. He and Andreas will 125read mail addressed to the png-implement list, however. 126 127Please do not send general questions about PNG. Send them to 128png-mng-misc at lists.sf.net (subscription required; visit 129https://lists.sourceforge.net/lists/listinfo/png-mng-misc to 130subscribe). If you have a question about something 131in the PNG specification that is related to using libpng, send it 132to me. Send me any questions that start with "I was using libpng, 133and ...". If in doubt, send questions to me. I'll bounce them 134to others, if necessary. 135 136Please do not send suggestions on how to change PNG. We have 137been discussing PNG for twenty years now, and it is official and 138finished. If you have suggestions for libpng, however, I'll 139gladly listen. Even if your suggestion is not used immediately, 140it may be used later. 141 142Files in this distribution: 143 144 ANNOUNCE => Announcement of this version, with recent changes 145 CHANGES => Description of changes between libpng versions 146 KNOWNBUG => List of known bugs and deficiencies 147 LICENSE => License to use and redistribute libpng 148 README => This file 149 TODO => Things not implemented in the current library 150 Y2KINFO => Statement of Y2K compliance 151 example.c => Example code for using libpng functions 152 libpng.3 => manual page for libpng (includes libpng-manual.txt) 153 libpng-manual.txt => Description of libpng and its functions 154 libpngpf.3 => manual page for libpng's private functions 155 png.5 => manual page for the PNG format 156 png.c => Basic interface functions common to library 157 png.h => Library function and interface declarations (public) 158 pngpriv.h => Library function and interface declarations (private) 159 pngconf.h => System specific library configuration (public) 160 pngstruct.h => png_struct declaration (private) 161 pnginfo.h => png_info struct declaration (private) 162 pngdebug.h => debugging macros (private) 163 pngerror.c => Error/warning message I/O functions 164 pngget.c => Functions for retrieving info from struct 165 pngmem.c => Memory handling functions 166 pngbar.png => PNG logo, 88x31 167 pngnow.png => PNG logo, 98x31 168 pngpread.c => Progressive reading functions 169 pngread.c => Read data/helper high-level functions 170 pngrio.c => Lowest-level data read I/O functions 171 pngrtran.c => Read data transformation functions 172 pngrutil.c => Read data utility functions 173 pngset.c => Functions for storing data into the info_struct 174 pngtest.c => Library test program 175 pngtest.png => Library test sample image 176 pngtrans.c => Common data transformation functions 177 pngwio.c => Lowest-level write I/O functions 178 pngwrite.c => High-level write functions 179 pngwtran.c => Write data transformations 180 pngwutil.c => Write utility functions 181 arm => Contains optimized code for the ARM platform 182 contrib => Contributions 183 arm-neon => Optimized code for ARM-NEON platform 184 examples => Example programs 185 gregbook => source code for PNG reading and writing, from 186 Greg Roelofs' "PNG: The Definitive Guide", 187 O'Reilly, 1999 188 intel => Optimized code for INTEL-SSE2 platform 189 libtests => Test programs 190 pngminim => Minimal decoder, encoder, and progressive decoder 191 programs demonstrating use of pngusr.dfa 192 pngminus => Simple pnm2png and png2pnm programs 193 pngsuite => Test images 194 testpngs 195 tools => Various tools 196 visupng => Contains a MSVC workspace for VisualPng 197 projects => Contains project files and workspaces for 198 building a DLL 199 owatcom => Contains a WATCOM project for building libpng 200 visualc71 => Contains a Microsoft Visual C++ (MSVC) 201 workspace for building libpng and zlib 202 vstudio => Contains a Microsoft Visual C++ (MSVC) 203 workspace for building libpng and zlib 204 scripts => Directory containing scripts for building libpng: 205 (see scripts/README.txt for the list of scripts) 206 207Good luck, and happy coding. 208 209-Glenn Randers-Pehrson (current maintainer, since 1998) 210 Internet: glennrp at users.sourceforge.net 211 212-Andreas Eric Dilger (former maintainer, 1996-1997) 213 Internet: adilger at enel.ucalgary.ca 214 Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/ 215 216-Guy Eric Schalnat (original author and former maintainer, 1995-1996) 217 (formerly of Group 42, Inc) 218 Internet: gschal at infinet.com 219
