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

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Tue, 29 Jun 2010 12:43:33 +0200
To: www-svg@w3.org
Message-Id: <201006291243.33346.Dr.O.Hoffmann@gmx.de>
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.'

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

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


Best wishes

Olaf
Received on Tuesday, 29 June 2010 10:46:12 GMT

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