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Re: [fxtf-drafts] [filter-effects] Require image re-sampling for feDisplacement

From: Dirk Schulze via GitHub <sysbot+gh@w3.org>
Date: Wed, 03 Jan 2018 10:44:06 +0000
To: public-fxtf-archive@w3.org
Message-ID: <issue_comment.created-354982760-1514976245-sysbot+gh@w3.org>
@AmeliaBR The Filter Effects spec is very clear about what should happen for undefined pixels (which may be the case for pixels that are actually not set by displacing the source input pixels to those pixels for example.)

> Sometimes filter primitives result in undefined pixels. For example, filter primitive feOffset can shift an image down and to the right, leaving undefined pixels at the top and left. In these cases, the undefined pixels are set to transparent black.

What you suggest is more in line of what I was thinking of what `image-rendering` is good for. What you describe is actually an image filter. Currently supported filters are nearest neighbor and bilinear interpolation. Of course there are more but they are not as commonly implemented in graphic libraries.

`feDisplacementMap` currently does not include a post processing step which does this interpolation you ask for. With the exception of `feImage` there is no image interpolation in use with the exception of rendering the last filter primitive result to screen. Here there _could_ be differences between interpolations though. And maybe that is what you saw for Firefox?

IMO an interpolation filter is a nice thing to have in certain situations but since there is no implementation experimenting for it, I would be in favour for deferring this request and adding it to the second level of the specification. What do you think?

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Received on Wednesday, 3 January 2018 10:44:07 UTC

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