[Bf-committers] Color space and alpha issues

[gespertino at gmail.com]

2011/12/22 Tobias Oelgarte <tobias.oelgarte at googlemail.com>:

> If that is the case then RGB+A should be always sufficient. I may not be
> 100% up to date, but could you construct a case in which this wouldn't
> be sufficient to do anything in non premultiplied alpha?

It's easy to see. Just render anything using straight alpha (which
afaik does exactly what you described) and try adding a 100px gaussian
blur.
Also remember that you won't be using only 3D renders in the
compositor. If you have chroma-keyed or rotoscoped live footage you'll
have background contaminating foreground in every convolution
operation. That has to be done with associated alpha.
Oh, and the candle example. With associated alpha the storage and
compositing of glowing objects is more effective (and you simply can't
store luminescent transparencies using an alpha mask).