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Re: luminanceToAlpha values in FEColorMatrix

From: Erik Dahlstrom <ed@opera.com>
Date: Mon, 12 Sep 2011 13:52:55 +0200
To: "Dean Jackson" <dino@apple.com>, "Chris Lilley" <chris@w3.org>
Cc: public-fx@w3.org, www-svg <www-svg@w3.org>
Message-ID: <op.v1o1yhrkgeuyw5@localhost.localdomain>
Hi Dean,

On Mon, 05 Sep 2011 22:41:09 +0200, Chris Lilley <chris@w3.org> wrote:

> On Friday, September 2, 2011, 3:10:53 AM, Dean wrote:
> DJ> It turns out there are a
> DJ> few different specifications for this. The closest to what is
> DJ> specified is in Rec. ITU-R BT.709-5 [1], but it is slightly  
> different:
> DJ>   0.2126 red, 0.7152 green, 0.0722 blue

I see that the filter draft was updated[1] recently to use the higher  
precision values, 0.2127 red, 0.7152 green, 0.0722 blue. That however sums  
to 1.0001, and we'd be better off using the above values instead (for the  
red channel). But looking ahead a bit I think it would be even better if  
we used the below figures instead.

> Those are the correct values (to 4 figures). For higher precision, the  
> values are 0.212656 0.715158 0.072186

I've not yet made any attempts to fix this, but I have created an action  
to do so[2].

[1] http://dvcs.w3.org/hg/FXTF/rev/b31bb9367aef
[2] http://www.w3.org/Graphics/fx/track/actions/53

Erik Dahlstrom, Core Technology Developer, Opera Software
Co-Chair, W3C SVG Working Group
Personal blog: http://my.opera.com/macdev_ed
Received on Monday, 12 September 2011 11:53:30 UTC

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