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Greg Roelofs - Subject: This is Register hype, nothing more [PNG Group] ( Nov 17, 2001, 05:35:38 )
The Register article is basically just their usual sensationalism (which, admittedly, is quite entertaining when it has to do with Microsoft). The PNG group (which includes at least one or two members of the W3C's SVG team, btw) did discuss the Apple patent several weeks ago, and we decided it was completely irrelevant to PNG itself, almost certainly irrelevant to the pnmtopng utility and to PNG's animated extension, MNG, and probably irrelevant to SVG, as well. And that's where the discussion--and the "perturbation"--ended, for the most part. In short, PNG alpha is identical to the version described in Porter and Duff's 1984 SIGGRAPH paper, which precedes Apple's filing by 8 years.
The web page referenced by The Register is part of Glenn Randers-Pehrson's "PNG and MNG Tools" site and is not in any sense "the group's." (If anything, the PNG home site, http://www.libpng.org/pub/png/ , is "the group's" official web site; I maintain that, with input from Glenn and many others.) Glenn happened to have more examples of prior art than anyone else and chose to set up a page listing them all, for which we can all be grateful. But The Register manages to infer more concern and more "officialness" than actually exists, in particular with respect to "the PNG effort" and a perceived need for a royalty-free license. PNG itself is completely clean. MNG and pnmtopng are probably clean, insofar as Apple's claims involve only mask images that are separate at the time of compositing. In any case, prior art for the grayscale-mask case almost certainly exists; it's only a matter of time before a definitive example is found and publicly revealed.
So I nominate this for the 2001 tempest-in-a-teapot award... But since the /. crowd lives for this stuff, I wouldn't presume to imagine that my comments will have any discernable effect on the (flame)festivities. :-)
Greg Roelofs
member, PNG Group; author, PNG: The Definitive Guide; maintainer, PNG and MNG home sites; hacker, lots of PNG-related tools
