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Re: [fxtf-drafts] [filter-effects] Browsers don't match spec for feDisplacementMap

From: Dirk Schulze via GitHub <sysbot+gh@w3.org>
Date: Sun, 31 Dec 2017 07:18:39 +0000
To: public-fxtf-archive@w3.org
Message-ID: <issue_comment.created-354589432-1514704718-sysbot+gh@w3.org>
@AmeliaBR Note: colors with 0 alpha is a special case. In your example, `feFlood` uses `flood-color="#888" flood-opacity="0"` so you know that you have a gray flooded area.

That is not what the implementations see. If we assume premultiplied colors, then all colors with opacity of 0 result in a color value of 0. There is no way to compute the original unpremuliply color anymore.

So your observation that for 0 alpha all implementations are operating on transparent black makes sense unless filter-effects would require to preserve the unpremultiplied color values of the input image which it currently doesn't. It just operates on un-premultiplied color values which means an implementation needs to convert premultiplied color values back to unpremultiplied color values.

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Received on Sunday, 31 December 2017 07:18:42 UTC

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