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Re: Algorithm for soft-light blend mode (ISSUE-2095)

From: Doug Schepers <schepers@w3.org>
Date: Wed, 08 Oct 2008 17:59:06 -0400
Message-ID: <48ED2D2A.7080609@w3.org>
To: Benjamin Otte <otte@gnome.org>
CC: www-svg@w3.org

Hi, Benjamin-

Thanks for bringing this to our attention.

Benjamin Otte wrote (on 10/8/08 2:02 PM):
> I'm in the process of implementing bend modes in the Cairo imaging
> library[1]. As Cairo is used as the renderer for a wide variety of
> formats, I wanted to have an as comprehensive list of blend modes as
> possible. 

Without looking too deeply into the issue, that seems like a reasonable

> And it turns out that the blend mode algorithms used are
> almost always equal. However, there is one exception: soft-light. The
> latest SVG draft specifies a different algorithm than PDF.
> So I was wondering if it was possible to change the algorithm in SVG
> to match the one of PDF, as that would solve a lot of problems.

Which SVG spec are you referencing (presumably the Filters module)?  Is
there a PDF spec you can point to, and how does it differ from SVG?

It's possible we could change it, though we'd have to look into the
reasons it's specified the way it is, and what the costs of changing it
would be.  Since SVG is a royalty-free language, that would also need to
be a consideration.

I've raised this as an issue for consideration [1], and any details you
could provide us would be helpful.

[1] http://www.w3.org/Graphics/SVG/WG/track/issues/2095

-Doug Schepers
W3C Team Contact, SVG and WebApps WGs
Received on Wednesday, 8 October 2008 21:59:44 UTC

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