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PNG programmers poo-poo Apple patent

Alpha blending IP 'irrelevant' to PNG, says community leading light

The PNG development community should not fear Apple's recently revealed alpha blending patent, a leading member of that band of coders has said.

Greg Roelofs, author of PNG: The Definitive Guide and a member of the PNG development team, this weekend said Apple's patent, number 5,379,129, was "irrelevant" to the ongoing evolution of PNG (Portable Network Graphics) format.

Writing in a LinuxToday discussion forum, Roelofs said: "The PNG group (which includes at least one or two members of the W3C's SVG team) 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."

It was Apple's revelation of pertinent intellectual property to the W3C-sponsored SVG development team that brought the patent to the attention of the PNG community. Apple reported its ownership of the technology - but declined to offer it to the SVG team on a royalty-free basis.

Patent number 5379129, filed by Apple in May 1992 and granted to the company in January 1995, describes a "method for compositing a source and destination image using a mask image". Essentially, it covers how computer software may blend two images using a third, the mask, to determine how the two are melded together.

The mask is usually a greyscale image, but Apple's patent extends to the use of full-colour masks.

Some member of the PNG community - including Glenn Randers-Pehrson, who also helps maintain the official PNG site, according to Roelofs - were sufficiently concerned about the Apple patent - and, in particular, the prospect of the Mac maker demanding royalties for PNG's alpha-blending support - that they posted online a list of prior art that "may be useful in overturning Apple's patent" and called on "Apple, Inc., to disclaim [the patent]" or grant the PNG team a royalty-free licence.

They needn't have bothered, Roelofs reckons. "PNG itself is completely clean," he writes. "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 greyscale-mask case almost certainly exists; it's only a matter of time before a definitive example is found and publicly revealed."

That's certainly the message we've heard from informed Register readers after we reported on the controversy last week. However, the ball's in Apple's court, and so far the company has been remarkably silent on the issue. It declined our invitation to comment. ®

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Related Links

Greg Roelofs on the Apple patent
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The official PNG site
W3C: SVG 1.0 Patent Statements

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