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Re: [SVG1.1F2 LC] 15.12 Filter primitive ‘feComposite’ formula

From: Erik Dahlstrom <ed@opera.com>
Date: Tue, 29 Jun 2010 13:18:01 +0200
To: www-svg@w3.org
Message-ID: <op.ve16z800geuyw5@localhost>
On Tue, 29 Jun 2010 12:43:33 +0200, Dr. Olaf Hoffmann  
<Dr.O.Hoffmann@gmx.de> wrote:

> Hello www-svg,
>
> about arithmetic operation of feComposite is mentioned:
>
> 'If the arithmetic operation is chosen, each result pixel is computed  
> using
> the following formula:
> result = k1*i1*i2 + k2*i1 + k3*i2 + k4'
>
> What is especially i1 and i2?
> My assumption is, that it is the value of the corresponding channel of
> the input indicated by the attributes in for i1 and in2 for i2?
> If this is correct, my suggestion is to add something like:
>
> ',where i1 and i2 indicate the corresponding pixel channel values of
> the input images, indicated by the attributes in for i1 and in2 for i2,
> and k1, k2, k3, k4 indicate the values of the attributes with the
> same name.'

Yes, the above is correct.

> Another suggestion to improve the understanding of the
> other operations is to add formulas for the other operations
> as well. This can help authors a lot, because the original
> article from Porter and Duff is not trivial to find for all readers,
> for example currently here an online version:
> http://keithp.com/~keithp/porterduff/p253-porter.pdf

What other operations? Where in the spec?

Are you suggesting adding all the porter-duff equations for 'over', 'xor'  
etc to the feComposite section?

> Additional suggestion for the related example:
> Add a generic font-family -
> Instead of font-family="Verdana" use for example
> font-family="Verdana, sans-serif"

Cosmetic change, but yes I agree, it is better practice.

Cheers
/Erik

-- 
Erik Dahlstrom, Core Technology Developer, Opera Software
Co-Chair, W3C SVG Working Group
Personal blog: http://my.opera.com/macdev_ed
Received on Tuesday, 29 June 2010 11:18:35 GMT

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