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The Register: Apple patents perturb PNG programmers

Nov 16, 2001, 19:38 (32 Talkback[s])
(Other stories by Tony Smith)
"Developers of the open source graphics format PNG and its derivative, MNG, have called on Apple to clarify whether its ownership of key PNG component technologies will be used to hinder their work.

At issue is patent number 5379129, filed by Apple in May 1992 and granted to the company in January 1995. The patent 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 process, known as 'alpha blending', is a common one in graphical manipulation. Games and multimedia applications use the technique to fade smoothly between one image and another. And Apple uses the technique to make Mac OS X's menus, dialog boxes and windows appear translucent."

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