The quantization and dithering code in pngquant is lifted from Jef Poskanzer's
'ppmquant', part of his wonderful PBMPLUS tool suite.

Greg Roelofs hacked it into a (in his words) "slightly cheesy" 'pamquant' back
in 1997 (see http://pobox.com/~newt/greg_rgba.html) and finally he ripped out
the cheesy file-I/O parts and replaced them with nice PNG code in December
2000. The PNG reading and writing code is a merged and slightly simplified
version of readpng, readpng2, and writepng from his book:

   "PNG: The Definitive Guide."

Pngquant therefore inherits both licenses, one for each source file.

Note that both licenses are basically BSD-like; that is, use the code however
you like, as long as you acknowledge its origins.

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pngquant.c:

   Copyright (C) 1989, 1991 by Jef Poskanzer.
   Copyright (C) 1997, 2000, 2002 by Greg Roelofs; based on an idea by
                                  Stefan Schneider.
   Copyright 2009-2012 by Kornel Lesinski.

   Permission to use, copy, modify, and distribute this software and its
   documentation for any purpose and without fee is hereby granted, provided
   that the above copyright notice appear in all copies and that both that
   copyright notice and this permission notice appear in supporting
   documentation.  This software is provided "as is" without express or
   implied warranty.

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rwpng.c (and rwpng.h):

   Copyright (c) 1998-2002 Greg Roelofs.  All rights reserved.

   This software is provided "as is," without warranty of any kind,
   express or implied.  In no event shall the author or contributors
   be held liable for any damages arising in any way from the use of
   this software.

   Permission is granted to anyone to use this software for any purpose,
   including commercial applications, and to alter it and redistribute
   it freely, subject to the following restrictions:

   1. Redistributions of source code must retain the above copyright
      notice, disclaimer, and this list of conditions.
   2. Redistributions in binary form must reproduce the above copyright
      notice, disclaimer, and this list of conditions in the documenta-
      tion and/or other materials provided with the distribution.
   3. All advertising materials mentioning features or use of this
      software must display the following acknowledgment:

         This product includes software developed by Greg Roelofs
         and contributors for the book, "PNG: The Definitive Guide,"
         published by O'Reilly and Associates.

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