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

Carlo Andreacchio carlorules at gmail.com
Tue Mar 10 22:27:55 CET 2015

Zauber, There is a "Use Alpha" option in the image texture settings which
disregards the alpha channel entirely.

>Well, that explains one problem of mine.  I use InsaneBump to generate
>some of the normal maps I use, and sometimes it generates them with an
>alpha channel (50% alpha on all pixels).  When it does this, the normal
>map becomes unusable with Cycles.

Jason, I actually wrote a patch which allowed this sort of operations --
https://developer.blender.org/D486 , From memory... The reason why it was
changed to the current function was that it was a hacky workaround, and
those sorts of workarounds should not be included in cycles.

> I've noticed Cycles always loads RGBA textures with black in the
transparent areas, as though the file was premultiplied. (Even if blender
itself is loading the file with straight alpha).
>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.
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