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Re: [ISSUE-2335] feConvolveMatrix bias property in SVG 1.1 SE

From: Jasper van de Gronde <th.v.d.gronde@hccnet.nl>
Date: Wed, 10 Nov 2010 11:15:23 +0100
Message-ID: <4CDA70BB.1080207@hccnet.nl>
To: Anthony Grasso <Anthony.Grasso@cisra.canon.com.au>
CC: "www-svg@w3.org" <www-svg@w3.org>, W3C SVG Public List <public-svg-wg@w3.org>
Hi,

I see the divisor as being nothing more or less than a convenient way of 
scaling the kernel, so not as a separate entity. So in the options I 
listed I assumed:
   cF = cO (*) (kernel/divisor)
   aF = aO (*) (kernel/divisor)
With (*) standing for convolution, and cO/aO for the original color and 
alpha channels. (With the F standing for filtered.)

Regards, Jasper

On 2010-11-10 02:06, Anthony Grasso wrote:
> Hi Jasper,
>
> I was given ACTION-2900 [1] to investigate the bias attribute.
>
> As you're aware the specification currently says when preserveAlpha="false" to apply the convolution to all channels. Currently in the specification, the formula to do the convolution for that case is:
>
> cR = (cF * kernel)/divisor + bias
> aR = (aF * kernal)/divisor + bias
>
> I agree that the definition of 'bias' is not clear at all and should be changed.
>
> Regarding how it is used in a filter mathematically, your options listed below do not take into account the filter 'divisor' that the current formula does. I would like to know where you think the 'divisor' value fits in with your options that you have specified.
>
> Cheers,
> Anthony
>
> [1] http://www.w3.org/Graphics/SVG/WG/track/actions/2900
> ...
 >> <quote>
 >> For reference, the pseudo-code in the SVG  specification suggests the
 >> following (preserveAlpha=false):
 >> -------------------------------------
 >> Option 1:
 >>     aF = filtered alpha without bias
 >>     cF = filtered (premultiplied) color without bias
 >>     aR = aF + bias
 >>     cR = cF + bias
 >> -------------------------------------
 >> ...
Received on Wednesday, 10 November 2010 10:15:54 GMT

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