1README for libpng version 1.6.37 - April 14, 2019 2================================================= 3 4See the note about version numbers near the top of png.h. 5See INSTALL for instructions on how to install libpng. 6 7Libpng comes in several distribution formats. Get libpng-*.tar.gz or 8libpng-*.tar.xz or if you want UNIX-style line endings in the text 9files, or lpng*.7z or lpng*.zip if you want DOS-style line endings. 10 11Version 0.89 was the first official release of libpng. Don't let the 12fact that it's the first release fool you. The libpng library has been 13in extensive use and testing since mid-1995. By late 1997 it had 14finally gotten to the stage where there hadn't been significant 15changes to the API in some time, and people have a bad feeling about 16libraries with versions < 1.0. Version 1.0.0 was released in 17March 1998. 18 19**** 20Note that some of the changes to the png_info structure render this 21version of the library binary incompatible with libpng-0.89 or 22earlier versions if you are using a shared library. The type of the 23"filler" parameter for png_set_filler() has changed from png_byte to 24png_uint_32, which will affect shared-library applications that use 25this function. 26 27To avoid problems with changes to the internals of the png info_struct, 28new APIs have been made available in 0.95 to avoid direct application 29access to info_ptr. These functions are the png_set_<chunk> and 30png_get_<chunk> functions. These functions should be used when 31accessing/storing the info_struct data, rather than manipulating it 32directly, to avoid such problems in the future. 33 34It is important to note that the APIs did not make current programs 35that access the info struct directly incompatible with the new 36library, through libpng-1.2.x. In libpng-1.4.x, which was meant to 37be a transitional release, members of the png_struct and the 38info_struct can still be accessed, but the compiler will issue a 39warning about deprecated usage. Since libpng-1.5.0, direct access 40to these structs is not allowed, and the definitions of the structs 41reside in private pngstruct.h and pnginfo.h header files that are not 42accessible to applications. It is strongly suggested that new 43programs use the new APIs (as shown in example.c and pngtest.c), and 44older programs be converted to the new format, to facilitate upgrades 45in the future. 46**** 47 48Additions since 0.90 include the ability to compile libpng as a 49Windows DLL, and new APIs for accessing data in the info struct. 50Experimental functions include the ability to set weighting and cost 51factors for row filter selection, direct reads of integers from buffers 52on big-endian processors that support misaligned data access, faster 53methods of doing alpha composition, and more accurate 16->8 bit color 54conversion. 55 56The additions since 0.89 include the ability to read from a PNG stream 57which has had some (or all) of the signature bytes read by the calling 58application. This also allows the reading of embedded PNG streams that 59do not have the PNG file signature. As well, it is now possible to set 60the library action on the detection of chunk CRC errors. It is possible 61to set different actions based on whether the CRC error occurred in a 62critical or an ancillary chunk. 63 64For a detailed description on using libpng, read libpng-manual.txt. 65For examples of libpng in a program, see example.c and pngtest.c. For 66usage information and restrictions (what little they are) on libpng, 67see png.h. For a description on using zlib (the compression library 68used by libpng) and zlib's restrictions, see zlib.h 69 70I have included a general makefile, as well as several machine and 71compiler specific ones, but you may have to modify one for your own 72needs. 73 74You should use zlib 1.0.4 or later to run this, but it MAY work with 75versions as old as zlib 0.95. Even so, there are bugs in older zlib 76versions which can cause the output of invalid compression streams for 77some images. 78 79You should also note that zlib is a compression library that is useful 80for more things than just PNG files. You can use zlib as a drop-in 81replacement for fread() and fwrite(), if you are so inclined. 82 83zlib should be available at the same place that libpng is, or at 84https://zlib.net. 85 86You may also want a copy of the PNG specification. It is available 87as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find 88these at http://www.libpng.org/pub/png/pngdocs.html . 89 90This code is currently being archived at libpng.sourceforge.io in the 91[DOWNLOAD] area, and at http://libpng.download/src . 92 93This release, based in a large way on Glenn's, Guy's and Andreas' 94earlier work, was created and will be supported by myself and the PNG 95development group. 96 97Send comments/corrections/commendations to png-mng-implement at 98lists.sourceforge.net (subscription required; visit 99https://lists.sourceforge.net/lists/listinfo/png-mng-implement 100to subscribe). 101 102Send general questions about the PNG specification to png-mng-misc 103at lists.sourceforge.net (subscription required; visit 104https://lists.sourceforge.net/lists/listinfo/png-mng-misc to 105subscribe). 106 107Files in this distribution: 108 109 ANNOUNCE => Announcement of this version, with recent changes 110 AUTHORS => List of contributing authors 111 CHANGES => Description of changes between libpng versions 112 KNOWNBUG => List of known bugs and deficiencies 113 LICENSE => License to use and redistribute libpng 114 README => This file 115 TODO => Things not implemented in the current library 116 TRADEMARK => Trademark information 117 example.c => Example code for using libpng functions 118 libpng.3 => manual page for libpng (includes libpng-manual.txt) 119 libpng-manual.txt => Description of libpng and its functions 120 libpngpf.3 => manual page for libpng's private functions 121 png.5 => manual page for the PNG format 122 png.c => Basic interface functions common to library 123 png.h => Library function and interface declarations (public) 124 pngpriv.h => Library function and interface declarations (private) 125 pngconf.h => System specific library configuration (public) 126 pngstruct.h => png_struct declaration (private) 127 pnginfo.h => png_info struct declaration (private) 128 pngdebug.h => debugging macros (private) 129 pngerror.c => Error/warning message I/O functions 130 pngget.c => Functions for retrieving info from struct 131 pngmem.c => Memory handling functions 132 pngbar.png => PNG logo, 88x31 133 pngnow.png => PNG logo, 98x31 134 pngpread.c => Progressive reading functions 135 pngread.c => Read data/helper high-level functions 136 pngrio.c => Lowest-level data read I/O functions 137 pngrtran.c => Read data transformation functions 138 pngrutil.c => Read data utility functions 139 pngset.c => Functions for storing data into the info_struct 140 pngtest.c => Library test program 141 pngtest.png => Library test sample image 142 pngtrans.c => Common data transformation functions 143 pngwio.c => Lowest-level write I/O functions 144 pngwrite.c => High-level write functions 145 pngwtran.c => Write data transformations 146 pngwutil.c => Write utility functions 147 arm => Contains optimized code for the ARM platform 148 powerpc => Contains optimized code for the PowerPC platform 149 contrib => Contributions 150 arm-neon => Optimized code for ARM-NEON platform 151 powerpc-vsx => Optimized code for POWERPC-VSX platform 152 examples => Example programs 153 gregbook => source code for PNG reading and writing, from 154 Greg Roelofs' "PNG: The Definitive Guide", 155 O'Reilly, 1999 156 libtests => Test programs 157 mips-msa => Optimized code for MIPS-MSA platform 158 pngminim => Minimal decoder, encoder, and progressive decoder 159 programs demonstrating use of pngusr.dfa 160 pngminus => Simple pnm2png and png2pnm programs 161 pngsuite => Test images 162 testpngs 163 tools => Various tools 164 visupng => Contains a MSVC workspace for VisualPng 165 intel => Optimized code for INTEL-SSE2 platform 166 mips => Optimized code for MIPS platform 167 projects => Contains project files and workspaces for 168 building a DLL 169 owatcom => Contains a WATCOM project for building libpng 170 visualc71 => Contains a Microsoft Visual C++ (MSVC) 171 workspace for building libpng and zlib 172 vstudio => Contains a Microsoft Visual C++ (MSVC) 173 workspace for building libpng and zlib 174 scripts => Directory containing scripts for building libpng: 175 (see scripts/README.txt for the list of scripts) 176 177Good luck, and happy coding! 178 179 * Cosmin Truta (current maintainer, since 2018) 180 * Glenn Randers-Pehrson (former maintainer, 1998-2018) 181 * Andreas Eric Dilger (former maintainer, 1996-1997) 182 * Guy Eric Schalnat (original author and former maintainer, 1995-1996) 183 (formerly of Group 42, Inc.) 184
