[Bf-committers] Compositing - We are doing it wrong (partially)

Troy Sobotka troy.sobotka at gmail.com
Mon May 14 15:28:24 CEST 2012

On May 14, 2012 4:37 AM, "Tobias Oelgarte"
<tobias.oelgarte<tobias.oelgarte at googlemail.com>
@ <tobias.oelgarte at googlemail.com>googlemail.com<tobias.oelgarte at googlemail.com>>
> This is partially wrong, since for masking you need sRGB values within
> the range of 0-1.

There are two assumptions here.

Alphas are strictly linear and should not be bound to any color space such
as sRGB.

The 0..1 clamp is required for both associated and unassociated alpha
compositing operation however.

Your point stands regarding the need to avoid linearization procedures.
There are currently three methods around this IIRC:

1) Use a proper linear file format that would avoid linearization. EXR.
2) Brecht provided a manual override to force a linear interpretation for
Cycles if memory serves for certain textures.
3) Saving into the correct alpha file channel in all formats will avoid the
sRGB linearization. Once inside Blender, that channel can be used as

With respect,

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