README (9476B)
1 README for libpng version 1.6.53 2 ================================ 3 4 See the note about version numbers near the top of `png.h`. 5 See `INSTALL` for instructions on how to install libpng. 6 7 Libpng comes in several distribution formats. Get `libpng-*.tar.gz` 8 or `libpng-*.tar.xz` if you want UNIX-style line endings in the text 9 files, or `lpng*.7z` or `lpng*.zip` if you want DOS-style line endings. 10 11 For a detailed description on using libpng, read `libpng-manual.txt`. 12 For examples of libpng in a program, see `example.c` and `pngtest.c`. 13 For usage information and restrictions (what little they are) on libpng, 14 see `png.h`. For a description on using zlib (the compression library 15 used by libpng) and zlib's restrictions, see `zlib.h`. 16 17 You should use zlib 1.0.4 or later to run this, but it _may_ work with 18 versions as old as zlib 0.95. Even so, there are bugs in older zlib 19 versions which can cause the output of invalid compression streams for 20 some images. 21 22 You should also note that zlib is a compression library that is useful 23 for more things than just PNG files. You can use zlib as a drop-in 24 replacement for `fread()` and `fwrite()`, if you are so inclined. 25 26 zlib should be available at the same place that libpng is, or at 27 https://zlib.net . 28 29 You may also want a copy of the PNG specification. It is available 30 as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find 31 these at http://www.libpng.org/pub/png/pngdocs.html . 32 33 This code is currently being archived at https://libpng.sourceforge.io 34 in the download area, and at http://libpng.download/src . 35 36 This release, based in a large way on Glenn's, Guy's and Andreas' 37 earlier work, was created and will be supported by myself and the PNG 38 development group. 39 40 Send comments, corrections and commendations to `png-mng-implement` 41 at `lists.sourceforge.net`. (Subscription is required; visit 42 https://lists.sourceforge.net/lists/listinfo/png-mng-implement 43 to subscribe.) 44 45 Send general questions about the PNG specification to `png-mng-misc` 46 at `lists.sourceforge.net`. (Subscription is required; visit 47 https://lists.sourceforge.net/lists/listinfo/png-mng-misc 48 to subscribe.) 49 50 Historical notes 51 ---------------- 52 53 The libpng library has been in extensive use and testing since mid-1995. 54 Version 0.89, published a year later, was the first official release. 55 By late 1997, it had finally gotten to the stage where there hadn't 56 been significant changes to the API in some time, and people have a bad 57 feeling about libraries with versions below 1.0. Version 1.0.0 was 58 released in March 1998. 59 60 Note that some of the changes to the `png_info` structure render this 61 version of the library binary incompatible with libpng-0.89 or 62 earlier versions if you are using a shared library. The type of the 63 `filler` parameter for `png_set_filler()` has changed from `png_byte` 64 to `png_uint_32`, which will affect shared-library applications that 65 use this function. 66 67 To avoid problems with changes to the internals of the `info_struct`, 68 new APIs have been made available in 0.95 to avoid direct application 69 access to `info_ptr`. These functions are the `png_set_<chunk>` and 70 `png_get_<chunk>` functions. These functions should be used when 71 accessing/storing the `info_struct` data, rather than manipulating it 72 directly, to avoid such problems in the future. 73 74 It is important to note that the APIs did not make current programs 75 that access the info struct directly incompatible with the new 76 library, through libpng-1.2.x. In libpng-1.4.x, which was meant to 77 be a transitional release, members of the `png_struct` and the 78 `info_struct` can still be accessed, but the compiler will issue a 79 warning about deprecated usage. Since libpng-1.5.0, direct access 80 to these structs is not allowed, and the definitions of the structs 81 reside in private `pngstruct.h` and `pnginfo.h` header files that are 82 not accessible to applications. It is strongly suggested that new 83 programs use the new APIs (as shown in `example.c` and `pngtest.c`), 84 and older programs be converted to the new format, to facilitate 85 upgrades in the future. 86 87 The additions since 0.89 include the ability to read from a PNG stream 88 which has had some (or all) of the signature bytes read by the calling 89 application. This also allows the reading of embedded PNG streams that 90 do not have the PNG file signature. As well, it is now possible to set 91 the library action on the detection of chunk CRC errors. It is possible 92 to set different actions based on whether the CRC error occurred in a 93 critical or an ancillary chunk. 94 95 The additions since 0.90 include the ability to compile libpng as a 96 Windows DLL, and new APIs for accessing data in the `info_struct`. 97 Experimental functions included the ability to set weighting and cost 98 factors for row filter selection, direct reads of integers from buffers 99 on big-endian processors that support misaligned data access, faster 100 methods of doing alpha composition, and more accurate 16-to-8 bit color 101 conversion. Some of these experimental functions, such as the weighted 102 filter heuristics, have since been removed. 103 104 Files included in this distribution 105 ----------------------------------- 106 107 ANNOUNCE => Announcement of this version, with recent changes 108 AUTHORS => List of contributing authors 109 CHANGES => Description of changes between libpng versions 110 INSTALL => Instructions to install libpng 111 LICENSE => License to use and redistribute libpng 112 README => This file 113 TODO => Things not implemented in the current library 114 TRADEMARK => Trademark information 115 example.c => Example code for using libpng functions 116 libpng.3 => Manual page for libpng (includes libpng-manual.txt) 117 libpng-manual.txt => Description of libpng and its functions 118 libpngpf.3 => Manual page for libpng's private functions (deprecated) 119 png.5 => Manual page for the PNG format 120 png.c => Basic interface functions common to library 121 png.h => Library function and interface declarations (public) 122 pngpriv.h => Library function and interface declarations (private) 123 pngconf.h => System specific library configuration (public) 124 pngstruct.h => png_struct declaration (private) 125 pnginfo.h => png_info struct declaration (private) 126 pngdebug.h => debugging macros (private) 127 pngerror.c => Error/warning message I/O functions 128 pngget.c => Functions for retrieving info from struct 129 pngmem.c => Memory handling functions 130 pngbar.png => PNG logo, 88x31 131 pngnow.png => PNG logo, 98x31 132 pngpread.c => Progressive reading functions 133 pngread.c => Read data/helper high-level functions 134 pngrio.c => Lowest-level data read I/O functions 135 pngrtran.c => Read data transformation functions 136 pngrutil.c => Read data utility functions 137 pngset.c => Functions for storing data into the info_struct 138 pngtest.c => Library test program 139 pngtest.png => Library test sample image 140 pngtrans.c => Common data transformation functions 141 pngwio.c => Lowest-level write I/O functions 142 pngwrite.c => High-level write functions 143 pngwtran.c => Write data transformations 144 pngwutil.c => Write utility functions 145 arm/ => Optimized code for ARM Neon 146 intel/ => Optimized code for INTEL SSE2 147 loongarch/ => Optimized code for LoongArch LSX 148 mips/ => Optimized code for MIPS MSA and MIPS MMI 149 powerpc/ => Optimized code for PowerPC VSX 150 riscv/ => Optimized code for the RISC-V platform 151 ci/ => Scripts for continuous integration 152 contrib/ => External contributions 153 arm-neon/ => Optimized code for the ARM-NEON platform 154 mips-msa/ => Optimized code for the MIPS-MSA platform 155 powerpc-vsx/ => Optimized code for the POWERPC-VSX platform 156 examples/ => Examples of libpng usage 157 gregbook/ => Source code for PNG reading and writing, from 158 "PNG: The Definitive Guide" by Greg Roelofs, 159 O'Reilly, 1999 160 libtests/ => Test programs 161 pngexif/ => Program to inspect the EXIF information in PNG files 162 pngminim/ => Minimal decoder, encoder, and progressive decoder 163 programs demonstrating the use of pngusr.dfa 164 pngminus/ => Simple pnm2png and png2pnm programs 165 pngsuite/ => Test images 166 riscv-rvv/ => Optimized code for the RISC-V Vector platform 167 testpngs/ => Test images 168 tools/ => Various tools 169 visupng/ => VisualPng, a Windows viewer for PNG images 170 projects/ => Project files and workspaces for various IDEs 171 owatcom/ => OpenWatcom project 172 visualc71/ => Microsoft Visual C++ 7.1 workspace 173 vstudio/ => Microsoft Visual Studio workspace 174 scripts/ => Scripts and makefiles for building libpng 175 (see scripts/README.txt for the complete list) 176 tests/ => Test scripts 177 178 Good luck, and happy coding! 179 180 * Cosmin Truta (current maintainer, since 2018) 181 * Glenn Randers-Pehrson (former maintainer, 1998-2018) 182 * Andreas Eric Dilger (former maintainer, 1996-1997) 183 * Guy Eric Schalnat (original author and former maintainer, 1995-1996) 184 (formerly of Group 42, Inc.)