Premultiplied colors and alpha=0
glynn at gclements.plus.com
Wed Aug 13 20:27:36 PDT 2008
Soeren Sandmann wrote:
> Generally to recover the "real" pixel from a premultiplied one, you
> have to divide by the alpha channel, but this leads to a problem when
> the alpha channel is 0. How should a render implementation treat such
> Suppose it is compositing a source pixel with alpha 0 and color
> channels non-zero
How is that supposed to happen?
If the colour channels have been pre-multiplied by the alpha, and the
alpha is zero, the colour channels will also be zero, no?
AIUI, the notion of pre-multiplication implies that none of the colour
channels can have a value which exceeds the alpha value.
Glynn Clements <glynn at gclements.plus.com>
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