libpng - free library for decoding PNG image format
README for libpng version 1.4.1 - February 25, 2010 (shared library 14.0) See the note about version numbers near the top of png.h
See INSTALL for instructions on how to install libpng.
Libpng comes in several distribution formats. Get libpng-*.tar.gz, libpng-*.tar.xz or libpng-*.tar.bz2 if you want UNIX-style line endings in the text files, or lpng*.zip if you want DOS-style line endings.
Version 0.89 was the first official release of libpng. Don't let the fact that it's the first release fool you. The libpng library has been in extensive use and testing since mid-1995. By late 1997 it had finally gotten to the stage where there hadn't been significant changes to the API in some time, and people have a bad feeling about libraries with versions < 1.0. Version 1.0.0 was released in March 1998.
Note that some of the changes to the png_info structure render this version of the library binary incompatible with libpng-0.89 or earlier versions if you are using a shared library. The type of the "filler" parameter for png_set_filler() has changed from png_byte to png_uint_32, which will affect shared-library applications that use this function.
To avoid problems with changes to the internals of png_info_struct, new APIs have been made available in 0.95 to avoid direct application access to info_ptr. These functions are the png_set_< chunk> and png_get_< chunk> functions. These functions should be used when accessing/storing the info_struct data, rather than manipulating it directly, to avoid such problems in the future.
It is important to note that the APIs do not make current programs that access the info struct directly incompatible with the new library. However, it is strongly suggested that new programs use the new APIs (as shown in example.c and pngtest.c), and older programs be converted to the new format, to facilitate upgrades in the future.
Additions since 0.90 include the ability to compile libpng as a Windows DLL, and new APIs for accessing data in the info struct. Experimental functions include the ability to set weighting and cost factors for row filter selection, direct reads of integers from buffers on big-endian processors that support misaligned data access, faster methods of doing alpha composition, and more accurate 16->8 bit color conversion.
The additions since 0.89 include the ability to read from a PNG stream which has had some (or all) of the signature bytes read by the calling application. This also allows the reading of embedded PNG streams that do not have the PNG file signature. As well, it is now possible to set the library action on the detection of chunk CRC errors. It is possible to set different actions based on whether the CRC error occurred in a critical or an ancillary chunk.
The changes made to the library, and bugs fixed are based on discussions on the PNG-implement mailing list and not on material submitted privately to Guy, Andreas, or Glenn. They will forward any good suggestions to the list.
For a detailed description on using libpng, read libpng.txt. For examples of libpng in a program, see example.c and pngtest.c. For usage information and restrictions (what little they are) on libpng, see png.h. For a description on using zlib (the compression library used by libpng) and zlib's restrictions, see zlib.h
I have included a general makefile, as well as several machine and compiler specific ones, but you may have to modify one for your own needs.
You should use zlib 1.0.4 or later to run this, but it MAY work with versions as old as zlib 0.95. Even so, there are bugs in older zlib versions which can cause the output of invalid compression streams for some images. You will definitely need zlib 1.0.4 or later if you are taking advantage of the MS-DOS "far" structure allocation for the small and medium memory models. You should also note that zlib is a compression library that is useful for more things than just PNG files. You can use zlib as a drop-in replacement for fread() and fwrite() if you are so inclined.
zlib should be available at the same place that libpng is, or at. ftp://ftp.info-zip.org/pub/infozip/zlib
You may also want a copy of the PNG specification. It is available as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find these at http://www.libpng.org/pub/png/documents/
This code is currently being archived at libpng.sf.net in the [DOWNLOAD] area, and on CompuServe, Lib 20 (PNG SUPPORT) at GO GRAPHSUP. If you can't find it in any of those places, e-mail me, and I'll help you find it.
If you have any code changes, requests, problems, etc., please e-mail them to me. Also, I'd appreciate any make files or project files, and any modifications you needed to make to get libpng to compile, along with a #define variable to tell what compiler/system you are on. If you needed to add transformations to libpng, or wish libpng would provide the image in a different way, drop me a note (and code, if possible), so I can consider supporting the transformation. Finally, if you get any warning messages when compiling libpng (note: not zlib), and they are easy to fix, I'd appreciate the fix. Please mention "libpng" somewhere in the subject line. Thanks.
This release was created and will be supported by myself (of course based in a large way on Guy's and Andreas' earlier work), and the PNG development group.
Send comments/corrections/commendations to png-mng-implement at lists.sourceforge.net (subscription required; visit these at https://lists.sourceforge.net/lists/listinfo/png-mng-implement to subscribe) or to glennrp at users.sourceforge.net
You can't reach Guy, the original libpng author, at the addresses given in previous versions of this document. He and Andreas will read mail addressed to the png-implement list, however.
Please do not send general questions about PNG. Send them to the (png-list at ccrc.wustl.edu, subscription required, write to majordomo at ccrc.wustl.edu with "subscribe png-list" in your message). On the other hand, please do not send libpng questions to that address, send them to me or to the png-implement list. I'll get them in the end anyway. If you have a question about something in the PNG specification that is related to using libpng, send it to me. Send me any questions that start with "I was using libpng, and ...". If in doubt, send questions to me. I'll bounce them to others, if necessary.
Please do not send suggestions on how to change PNG. We have been discussing PNG for nine years now, and it is official and finished. If you have suggestions for libpng, however, I'll gladly listen. Even if your suggestion is not used immediately, it may be used later.
Good luck, and happy coding.
-Glenn Randers-Pehrson (current maintainer, since 1998) Internet: glennrp at users.sourceforge.net
-Andreas Eric Dilger (former maintainer, 1996-1997) Internet: adilger at enel.ucalgary.ca Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
-Guy Eric Schalnat (original author and former maintainer, 1995-1996) (formerly of Group 42, Inc) Internet: gschal at infinet.com