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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 06:56:10 +0000
To: public-fxtf-archive@w3.org
Message-ID: <issue_comment.created-354588738-1514703369-sysbot+gh@w3.org>
@AmeliaBR To summarize your confusion with the spec text: You are asking if implementations should use premultiplied colors or non-premultiplied colors when selecting the channels R, G or B?

The introduction (https://drafts.fxtf.org/filter-effects/#FilterPrimitivesOverviewIntro) states that all primitives operate with premultiplied colors unless stated differently. 

`feDisplacementMap` actually defines it pretty clear:

> The input image in is to remain premultiplied for this filter primitive. The calculations using the pixel values from in2 are performed using non-premultiplied color values.

So no scaling by alpha from in2, the displacement map, for R, G or B channel. If implementations do so, then they are in mistake. Quite frankly, I personally would not think that we should change the specification text here. Using premultiplied colors from the displacement map is logically incorrect.

What we should do is writing tests (which you did) and report issues to browser vendors.

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Received on Sunday, 31 December 2017 06:56:15 UTC

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