[Bf-cycles] Cycles loads RGBA textures "premultiplied"?

Troy Sobotka troy.sobotka at gmail.com
Tue Mar 10 22:40:38 CET 2015

On Mar 10, 2015 1:44 PM, "Jason Clarke" <jason.clarke0 at gmail.com> wrote:
> Why does it do this? Is there a way to disable it? It makes it impossible
to store anything in a texture's alpha channel except actual transparency.
Trying to store something like bump or roughness data in the alpha channel
will ruin whatever is being stored in the RGB side.

Technically I believe it assumes associated alpha. This is because
associated alpha is the only correct method to represent light, and as
such, OIIO relies on this implementation.

That said, associated alpha doesn't prevent you from storing values in the
RGB data with zero transparency. A set such as 13.5,0.0,0.0 with an alpha
of 0.0 is perfectly valid, representing pixel with no occlusion and
emitting light.

I would think this has more to do with your chosen file format perhaps?
Have you tried with EXRs?

With respect,
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