If you are interested in learning more about the PNG format, definitely check out PNG: The Definitive Guide (O'Reilly, 1999) by Greg Roelofs. Many thanks to go Greg for his generous contributions to this chapter.
There are also a few good resources available online:
http://www.libpng.org/pub/png/
This site is written and maintained by Greg Roelofs. It contains a complete history of PNG's birth, descriptions of its features, and up-to-date lists of applications that support the new format. It also includes a copy of the PNG Specification and the official PNG extensions documents (as well as the draft MNG Spec). All of it is written with so much enthusiasm that you can't help but become a PNG fan! It is the source of much of the information in this chapter.
This is the complete PNG specification (Version 1.0) as published by the W3C. For a technical document, it is very user-friendly to nonprogrammers and offers detailed information on how PNGs work, as well as some useful background information and tutorials. The updated Version 1.2 of the specification is available at the PNG web site at http://www.libpng.org/pub/png/spec/.
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