| 1 | README for libpng version 1.6.43
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| 2 | ================================
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| 3 |
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| 4 | See the note about version numbers near the top of `png.h`.
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| 5 | See `INSTALL` for instructions on how to install libpng.
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| 6 |
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| 7 | Libpng comes in several distribution formats. Get `libpng-*.tar.gz`
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| 8 | or `libpng-*.tar.xz` if you want UNIX-style line endings in the text
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| 9 | files, or `lpng*.7z` or `lpng*.zip` if you want DOS-style line endings.
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| 10 |
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| 11 | For a detailed description on using libpng, read `libpng-manual.txt`.
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| 12 | For examples of libpng in a program, see `example.c` and `pngtest.c`.
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| 13 | For usage information and restrictions (what little they are) on libpng,
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| 14 | see `png.h`. For a description on using zlib (the compression library
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| 15 | used by libpng) and zlib's restrictions, see `zlib.h`.
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| 16 |
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| 17 | You should use zlib 1.0.4 or later to run this, but it _may_ work with
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| 18 | versions as old as zlib 0.95. Even so, there are bugs in older zlib
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| 19 | versions which can cause the output of invalid compression streams for
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| 20 | some images.
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| 21 |
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| 22 | You should also note that zlib is a compression library that is useful
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| 23 | for more things than just PNG files. You can use zlib as a drop-in
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| 24 | replacement for `fread()` and `fwrite()`, if you are so inclined.
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| 25 |
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| 26 | zlib should be available at the same place that libpng is, or at
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| 27 | https://zlib.net .
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| 28 |
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| 29 | You may also want a copy of the PNG specification. It is available
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| 30 | as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find
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| 31 | these at http://www.libpng.org/pub/png/pngdocs.html .
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| 32 |
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| 33 | This code is currently being archived at https://libpng.sourceforge.io
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| 34 | in the download area, and at http://libpng.download/src .
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| 35 |
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| 36 | This release, based in a large way on Glenn's, Guy's and Andreas'
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| 37 | earlier work, was created and will be supported by myself and the PNG
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| 38 | development group.
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| 39 |
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| 40 | Send comments, corrections and commendations to `png-mng-implement`
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| 41 | at `lists.sourceforge.net`. (Subscription is required; visit
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| 42 | https://lists.sourceforge.net/lists/listinfo/png-mng-implement
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| 43 | to subscribe.)
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| 44 |
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| 45 | Send general questions about the PNG specification to `png-mng-misc`
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| 46 | at `lists.sourceforge.net`. (Subscription is required; visit
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| 47 | https://lists.sourceforge.net/lists/listinfo/png-mng-misc
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| 48 | to subscribe.)
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| 49 |
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| 50 | Historical notes
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| 51 | ----------------
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| 52 |
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| 53 | The libpng library has been in extensive use and testing since mid-1995.
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| 54 | Version 0.89, published a year later, was the first official release.
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| 55 | By late 1997, it had finally gotten to the stage where there hadn't
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| 56 | been significant changes to the API in some time, and people have a bad
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| 57 | feeling about libraries with versions below 1.0. Version 1.0.0 was
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| 58 | released in March 1998.
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| 59 |
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| 60 | Note that some of the changes to the `png_info` structure render this
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| 61 | version of the library binary incompatible with libpng-0.89 or
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| 62 | earlier versions if you are using a shared library. The type of the
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| 63 | `filler` parameter for `png_set_filler()` has changed from `png_byte`
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| 64 | to `png_uint_32`, which will affect shared-library applications that
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| 65 | use this function.
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| 66 |
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| 67 | To avoid problems with changes to the internals of the `info_struct`,
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| 68 | new APIs have been made available in 0.95 to avoid direct application
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| 69 | access to `info_ptr`. These functions are the `png_set_<chunk>` and
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| 70 | `png_get_<chunk>` functions. These functions should be used when
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| 71 | accessing/storing the `info_struct` data, rather than manipulating it
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| 72 | directly, to avoid such problems in the future.
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| 73 |
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| 74 | It is important to note that the APIs did not make current programs
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| 75 | that access the info struct directly incompatible with the new
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| 76 | library, through libpng-1.2.x. In libpng-1.4.x, which was meant to
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| 77 | be a transitional release, members of the `png_struct` and the
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| 78 | `info_struct` can still be accessed, but the compiler will issue a
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| 79 | warning about deprecated usage. Since libpng-1.5.0, direct access
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| 80 | to these structs is not allowed, and the definitions of the structs
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| 81 | reside in private `pngstruct.h` and `pnginfo.h` header files that are
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| 82 | not accessible to applications. It is strongly suggested that new
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| 83 | programs use the new APIs (as shown in `example.c` and `pngtest.c`),
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| 84 | and older programs be converted to the new format, to facilitate
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| 85 | upgrades in the future.
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| 86 |
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| 87 | The additions since 0.89 include the ability to read from a PNG stream
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| 88 | which has had some (or all) of the signature bytes read by the calling
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| 89 | application. This also allows the reading of embedded PNG streams that
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| 90 | do not have the PNG file signature. As well, it is now possible to set
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| 91 | the library action on the detection of chunk CRC errors. It is possible
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| 92 | to set different actions based on whether the CRC error occurred in a
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| 93 | critical or an ancillary chunk.
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| 94 |
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| 95 | The additions since 0.90 include the ability to compile libpng as a
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| 96 | Windows DLL, and new APIs for accessing data in the `info_struct`.
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| 97 | Experimental functions included the ability to set weighting and cost
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| 98 | factors for row filter selection, direct reads of integers from buffers
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| 99 | on big-endian processors that support misaligned data access, faster
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| 100 | methods of doing alpha composition, and more accurate 16-to-8 bit color
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| 101 | conversion. Some of these experimental functions, such as the weighted
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| 102 | filter heuristics, have since been removed.
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| 103 |
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| 104 | Files included in this distribution
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| 105 | -----------------------------------
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| 106 |
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| 107 | ANNOUNCE => Announcement of this version, with recent changes
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| 108 | AUTHORS => List of contributing authors
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| 109 | CHANGES => Description of changes between libpng versions
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| 110 | INSTALL => Instructions to install libpng
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| 111 | LICENSE => License to use and redistribute libpng
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| 112 | README => This file
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| 113 | TODO => Things not implemented in the current library
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| 114 | TRADEMARK => Trademark information
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| 115 | example.c => Example code for using libpng functions
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| 116 | libpng.3 => Manual page for libpng (includes libpng-manual.txt)
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| 117 | libpng-manual.txt => Description of libpng and its functions
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| 118 | libpngpf.3 => Manual page for libpng's private functions (deprecated)
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| 119 | png.5 => Manual page for the PNG format
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| 120 | png.c => Basic interface functions common to library
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| 121 | png.h => Library function and interface declarations (public)
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| 122 | pngpriv.h => Library function and interface declarations (private)
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| 123 | pngconf.h => System specific library configuration (public)
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| 124 | pngstruct.h => png_struct declaration (private)
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| 125 | pnginfo.h => png_info struct declaration (private)
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| 126 | pngdebug.h => debugging macros (private)
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| 127 | pngerror.c => Error/warning message I/O functions
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| 128 | pngget.c => Functions for retrieving info from struct
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| 129 | pngmem.c => Memory handling functions
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| 130 | pngbar.png => PNG logo, 88x31
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| 131 | pngnow.png => PNG logo, 98x31
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| 132 | pngpread.c => Progressive reading functions
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| 133 | pngread.c => Read data/helper high-level functions
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| 134 | pngrio.c => Lowest-level data read I/O functions
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| 135 | pngrtran.c => Read data transformation functions
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| 136 | pngrutil.c => Read data utility functions
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| 137 | pngset.c => Functions for storing data into the info_struct
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| 138 | pngtest.c => Library test program
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| 139 | pngtest.png => Library test sample image
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| 140 | pngtrans.c => Common data transformation functions
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| 141 | pngwio.c => Lowest-level write I/O functions
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| 142 | pngwrite.c => High-level write functions
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| 143 | pngwtran.c => Write data transformations
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| 144 | pngwutil.c => Write utility functions
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| 145 | arm/ => Optimized code for ARM Neon
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| 146 | intel/ => Optimized code for INTEL SSE2
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| 147 | loongarch/ => Optimized code for LoongArch LSX
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| 148 | mips/ => Optimized code for MIPS MSA and MIPS MMI
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| 149 | powerpc/ => Optimized code for PowerPC VSX
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| 150 | ci/ => Scripts for continuous integration
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| 151 | contrib/ => External contributions
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| 152 | arm-neon/ => Optimized code for the ARM-NEON platform
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| 153 | mips-msa/ => Optimized code for the MIPS-MSA platform
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| 154 | powerpc-vsx/ => Optimized code for the POWERPC-VSX platform
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| 155 | examples/ => Examples of libpng usage
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| 156 | gregbook/ => Source code for PNG reading and writing, from
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| 157 | "PNG: The Definitive Guide" by Greg Roelofs,
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| 158 | O'Reilly, 1999
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| 159 | libtests/ => Test programs
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| 160 | oss-fuzz/ => Files used by the OSS-Fuzz project for fuzz-testing
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| 161 | libpng
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| 162 | pngexif/ => Program to inspect the EXIF information in PNG files
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| 163 | pngminim/ => Minimal decoder, encoder, and progressive decoder
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| 164 | programs demonstrating the use of pngusr.dfa
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| 165 | pngminus/ => Simple pnm2png and png2pnm programs
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| 166 | pngsuite/ => Test images
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| 167 | testpngs/ => Test images
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| 168 | tools/ => Various tools
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| 169 | visupng/ => VisualPng, a Windows viewer for PNG images
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| 170 | projects/ => Project files and workspaces for various IDEs
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| 171 | owatcom/ => OpenWatcom project
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| 172 | visualc71/ => Microsoft Visual C++ 7.1 workspace
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| 173 | vstudio/ => Microsoft Visual Studio workspace
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| 174 | scripts/ => Scripts and makefiles for building libpng
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| 175 | (see scripts/README.txt for the complete list)
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| 176 | tests/ => Test scripts
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| 177 |
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| 178 | Good luck, and happy coding!
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| 179 |
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| 180 | * Cosmin Truta (current maintainer, since 2018)
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| 181 | * Glenn Randers-Pehrson (former maintainer, 1998-2018)
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| 182 | * Andreas Eric Dilger (former maintainer, 1996-1997)
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| 183 | * Guy Eric Schalnat (original author and former maintainer, 1995-1996)
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| 184 | (formerly of Group 42, Inc.)
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