GNU bug report logs - #59242
29.0.50; Poor quality for WebP images

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Message #13 received at control <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Po Lu <luangruo <at> yahoo.com>
Cc: 59242 <at> debbugs.gnu.org, Evgeny Zajcev <lg.zevlg <at> gmail.com>
Subject: Re: bug#59242: 29.0.50; Poor quality for WebP images
Date: Mon, 14 Aug 2023 02:11:56 +0200

[Message part 1 (text/plain, inline)]

tags 59242 + patch
thanks

Po Lu <luangruo <at> yahoo.com> writes:

> > Evgeny Zajcev <lg.zevlg <at> gmail.com> writes:
>
> > Looks like partial transparency is incorrectly applied for webp images.

Thanks for the bug report.

> Stefan, I see the following code in image.c:
[...]
> So if the webp library does not blend itself, I think we will have to do
> that for it.  Am I missing anything here?

Yes, the old code was not right.  The attached patch should add proper
alpha blending for webp images.  I have tested it with the example
images here: https://developers.google.com/speed/webp/gallery2

Evgeny, could you please test this patch and report back?  It should
apply cleanly both against master and emacs-29.

[0001-Fix-alpha-blending-for-webp-images.patch (application/x-patch, attachment)]

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