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README for libpng version 1.6.20 - December 3, 2015 (shared library 16.0) 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 or libpng-*.tar.xz or if you want UNIX-style line endings in the text files, or lpng*.7z 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 did not make current programs that access the info struct directly incompatible with the new library, through libpng-1.2.x. In libpng-1.4.x, which was meant to be a transitional release, members of the png_struct and the info_struct can still be accessed, but the compiler will issue a warning about deprecated usage. Since libpng-1.5.0, direct access to these structs is not allowed, and the definitions of the structs reside in private pngstruct.h and pnginfo.h header files that are not accessible to applications. 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-manual.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 zlib.net. 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 at ftp://ftp.simplesystems.org. If you can't find it in any of those places, e-mail me, and I'll help you find it. I am not a lawyer, but I believe that the Export Control Classification Number (ECCN) for libpng is EAR99, which means not subject to export controls or International Traffic in Arms Regulations (ITAR) because it is open source, publicly available software, that does not contain any encryption software. See the EAR, paragraphs 734.3(b)(3) and 734.7(b). 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 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 png-mng-misc at lists.sf.net (subscription required; visit https://lists.sourceforge.net/lists/listinfo/png-mng-misc to subscribe). 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 twenty 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. Files in this distribution: ANNOUNCE => Announcement of this version, with recent changes CHANGES => Description of changes between libpng versions KNOWNBUG => List of known bugs and deficiencies LICENSE => License to use and redistribute libpng README => This file TODO => Things not implemented in the current library Y2KINFO => Statement of Y2K compliance example.c => Example code for using libpng functions libpng.3 => manual page for libpng (includes libpng-manual.txt) libpng-manual.txt => Description of libpng and its functions libpngpf.3 => manual page for libpng's private functions png.5 => manual page for the PNG format png.c => Basic interface functions common to library png.h => Library function and interface declarations (public) pngpriv.h => Library function and interface declarations (private) pngconf.h => System specific library configuration (public) pngstruct.h => png_struct declaration (private) pnginfo.h => png_info struct declaration (private) pngdebug.h => debugging macros (private) pngerror.c => Error/warning message I/O functions pngget.c => Functions for retrieving info from struct pngmem.c => Memory handling functions pngbar.png => PNG logo, 88x31 pngnow.png => PNG logo, 98x31 pngpread.c => Progressive reading functions pngread.c => Read data/helper high-level functions pngrio.c => Lowest-level data read I/O functions pngrtran.c => Read data transformation functions pngrutil.c => Read data utility functions pngset.c => Functions for storing data into the info_struct pngtest.c => Library test program pngtest.png => Library test sample image pngtrans.c => Common data transformation functions pngwio.c => Lowest-level write I/O functions pngwrite.c => High-level write functions pngwtran.c => Write data transformations pngwutil.c => Write utility functions arm => Contains optimized code for the ARM platform contrib => Contributions examples => Example programs gregbook => source code for PNG reading and writing, from Greg Roelofs' "PNG: The Definitive Guide", O'Reilly, 1999 libtests => Test programs pngminim => Minimal decoder, encoder, and progressive decoder programs demonstrating use of pngusr.dfa pngminus => Simple pnm2png and png2pnm programs pngsuite => Test images tools => Various tools visupng => Contains a MSVC workspace for VisualPng projects => Contains project files and workspaces for building a DLL owatcom => Contains a WATCOM project for building libpng visualc71 => Contains a Microsoft Visual C++ (MSVC) workspace for building libpng and zlib vstudio => Contains a Microsoft Visual C++ (MSVC) workspace for building libpng and zlib scripts => Directory containing scripts for building libpng: (see scripts/README.txt for the list of scripts) 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