PngSuite - Zlib compression / GIF-files
z00n2c08 - color, no interlacing, compression level 0 (none)
z03n2c08 - color, no interlacing, compression level 3
z06n2c08 - color, no interlacing, compression level 6 (default)
z09n2c08 - color, no interlacing, compression level 9 (maximum)
Willem van Schaik, Calgary, April 2011
http://www.schaik.com/wwwillem.html