[Bf-committers] Color Unpremultiply

[gespertino at gmail.com]

2012/2/18 Troy Sobotka <troy.sobotka at gmail.com>

> I always feel like a low rent chess player speaking with a grandmaster when
> I am speaking with Brecht,
>

+1 :-)

I tried to find information about RGBA images matted with arbitrary colors,
and I can't find a good explanation about why or when they are necessary.
As far as I can tell, an image composited on white, gray, or any other
color is nothing but an unassociated alpha image, despite being called
"premultiplied with color" by some applications (like Adobe suite).
So why does "unpremultiplication" appy here? An unassociated alpha image
shouldn't have to be "unpremultiplied" because it's not a premultiplied
image.

If an unassociated alpha image requieres some sort of "key" value to revert
color contamination in semitransparent pixels it's a completely different
issue, and not related with the division needed to color correct linear
RGBA.

Kind regards.
Gez