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@@ -1,56 +1,88 @@ -README for libpng version 1.6.34 - September 29, 2017 (shared library 16.0) -See the note about version numbers near the top of png.h +README for libpng version 1.6.40 +================================ -See INSTALL for instructions on how to install libpng. +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. +Libpng comes in several distribution formats. Get `libpng-*.tar.gz` +or `libpng-*.tar.xz` 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. +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`. -**** -Note that some of the changes to the png_info structure render this +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 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 +https://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/pngdocs.html . + +This code is currently being archived at https://libpng.sourceforge.io +in the download area, and at http://libpng.download/src . + +This release, based in a large way on Glenn's, Guy's and Andreas' +earlier work, was created and will be supported by myself and the PNG +development group. + +Send comments, corrections and commendations to `png-mng-implement` +at `lists.sourceforge.net`. (Subscription is required; visit +https://lists.sourceforge.net/lists/listinfo/png-mng-implement +to subscribe.) + +Send general questions about the PNG specification to `png-mng-misc` +at `lists.sourceforge.net`. (Subscription is required; visit +https://lists.sourceforge.net/lists/listinfo/png-mng-misc +to subscribe.) + +Historical notes +---------------- + +The libpng library has been in extensive use and testing since mid-1995. +Version 0.89, published a year later, was the first official release. +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 below 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. +`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 the png info_struct, +To avoid problems with changes to the internals of the `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 +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 +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. +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. 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 @@ -60,163 +92,91 @@ 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/pngdocs.html . - -This code is currently being archived at libpng.sourceforge.io in the -[DOWNLOAD] area, and at http://libpng.download/src . 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 - powerpc => Contains optimized code for the PowerPC platform - contrib => Contributions - arm-neon => Optimized code for ARM-NEON platform - powerpc-vsx => Optimized code for POWERPC-VSX platform - examples => Example programs - gregbook => source code for PNG reading and writing, from - Greg Roelofs' "PNG: The Definitive Guide", - O'Reilly, 1999 - libtests => Test programs - mips-msa => Optimized code for MIPS-MSA platform - pngminim => Minimal decoder, encoder, and progressive decoder - programs demonstrating use of pngusr.dfa - pngminus => Simple pnm2png and png2pnm programs - pngsuite => Test images - testpngs - tools => Various tools - visupng => Contains a MSVC workspace for VisualPng - intel => Optimized code for INTEL-SSE2 platform - mips => Optimized code for MIPS platform - 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 +The 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 included 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-to-8 bit color +conversion. Some of these experimental functions, such as the weighted +filter heuristics, have since been removed. + +Files included in this distribution +----------------------------------- + + ANNOUNCE => Announcement of this version, with recent changes + AUTHORS => List of contributing authors + CHANGES => Description of changes between libpng versions + INSTALL => Instructions to install libpng + LICENSE => License to use and redistribute libpng + README => This file + TODO => Things not implemented in the current library + TRADEMARK => Trademark information + 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 (deprecated) + 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/ => Optimized code for the ARM platform + intel/ => Optimized code for the INTEL-SSE2 platform + mips/ => Optimized code for the MIPS platform + powerpc/ => Optimized code for the PowerPC platform + ci/ => Scripts for continuous integration + contrib/ => External contributions + arm-neon/ => Optimized code for the ARM-NEON platform + mips-msa/ => Optimized code for the MIPS-MSA platform + powerpc-vsx/ => Optimized code for the POWERPC-VSX platform + examples/ => Examples of libpng usage + gregbook/ => Source code for PNG reading and writing, from + "PNG: The Definitive Guide" by Greg Roelofs, + O'Reilly, 1999 + libtests/ => Test programs + oss-fuzz/ => Files used by the OSS-Fuzz project for fuzz-testing + libpng + pngminim/ => Minimal decoder, encoder, and progressive decoder + programs demonstrating the use of pngusr.dfa + pngminus/ => Simple pnm2png and png2pnm programs + pngsuite/ => Test images + testpngs/ => Test images + tools/ => Various tools + visupng/ => VisualPng, a Windows viewer for PNG images + projects/ => Project files and workspaces for various IDEs + owatcom/ => OpenWatcom project + visualc71/ => Microsoft Visual C++ 7.1 workspace + vstudio/ => Microsoft Visual Studio workspace + scripts/ => Scripts and makefiles for building libpng + (see scripts/README.txt for the complete list) + tests/ => Test scripts + +Good luck, and happy coding! + + * Cosmin Truta (current maintainer, since 2018) + * Glenn Randers-Pehrson (former maintainer, 1998-2018) + * Andreas Eric Dilger (former maintainer, 1996-1997) + * Guy Eric Schalnat (original author and former maintainer, 1995-1996) + (formerly of Group 42, Inc.) |