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Re: luminanceToAlpha values in FEColorMatrix

From: Dean Jackson <dino@apple.com>
Date: Tue, 13 Sep 2011 05:36:05 +1000
Cc: Chris Lilley <chris@w3.org>, public-fx@w3.org, www-svg <www-svg@w3.org>
Message-id: <70746D49-E89D-4969-B13E-986DD25DD4BB@apple.com>
To: Erik Dahlstrom <ed@opera.com>

On 12/09/2011, at 9:52 PM, Erik Dahlstrom wrote:

> 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,

My fault! I'll fix it if you don't get to it soon. I'd like to keep it at 4 digits if possible.

BTW - I found some internal Apple code that used the old values so I did some digging. Peter Graffagnino (ex-Apple, the father of filters) sent them in his filters proposal on 17th June 1999 [1]

Dean

[1] http://lists.w3.org/Archives/Member/w3c-svg-wg/1999AprJun/0362.html

> 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 19:36:49 GMT

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