Changing the Alpha Mode of an Image in Cycles doesn't have expected effect. #53672
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Reference: blender/blender#53672
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Images with non-color data such as normal maps that also have an alpha channel containing other data such as a bump map have the color data affected by the alpha channel, even when the Alpha Mode is set to Straight.
When the alpha channel on the image is disabled or when the image file has the alpha channel removed the texture behaves as expected, but this prevents using the data in the alpha channel.
Using Blender 2.79 Cycles renderer.
alphapremult.blend
Added subscriber: @isalegend
#58083 was marked as duplicate of this issue
#55259 was marked as duplicate of this issue
Added subscribers: @Sergey, @lichtwerk
I can confirm this behaviour and would also expect 'straight' alpha mode to not affect color data.
Maybe @Sergey can have a look?
Added subscriber: @brecht
I'll fix it so we don't premultiply alpha for non-color data. For the OSL / OIIO texture cache case this might be complicated.
Added subscriber: @omgold
Until this is fixed, there is a workaround:
Didn't check, though, whether this will double memory usage.
Added subscribers: @AlmaTalp, @StephenSwaney, @moisessalvador
If I could have a note: it would be great to make it work properly both for 'Color' and 'Non-Color' data as very specific usage could happen sometimes. Thanks.
It can only work for Non-Color, as alpha must be premultiplied for correct texture filtering of colors and alpha.
In Unity an RGBA image could be imported with some extra settings; on of it that 'how to use the alpha'. When transparency needed, it acts like alpha, when it is an additional data channel, it acts as a greyscale channel.
Sorry for citing Unity; it is because of the flawless workflow in the pipeline.
BTW Marmoset works similarly.
Added subscriber: @Mets
Added subscriber: @filibis
Added subscriber: @Interference
This issue was referenced by blender/cycles@f8b3f970d2
This issue was referenced by
7aaa7aa9dd
Changed status from 'Open' to: 'Resolved'