Changing the Alpha Mode of an Image in Cycles doesn't have expected effect. #53672

New Issue

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

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](https://archive.blender.org/developer/F1644642/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?

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:

create two image texture nodes, referencing both the same image (note: this is not the same as duplicating the texture node).
check 'Use Alpha' for the first, uncheck it for the second
use the first node to connect RGB, the second to connect alpha.

Didn't check, though, whether this will double memory usage.

Until this is fixed, there is a workaround: - create two image texture nodes, referencing both the same image (note: this is not the same as duplicating the texture node). - check 'Use Alpha' for the first, uncheck it for the second - use the first node to connect RGB, the second to connect alpha. 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.

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. ![Unity Tex Import 02.png](https://archive.blender.org/developer/F5735468/Unity_Tex_Import_02.png) ![Unity Tex Import 01.png](https://archive.blender.org/developer/F5735469/Unity_Tex_Import_01.png)

Added subscriber: @Mets

Added subscriber: @filibis

Added subscriber: @Interference

This issue was referenced by blender/cycles@f8b3f970d2

This issue was referenced by blender/cycles@f8b3f970d2b54c73a4e1e33585176ea66ccf7bff

This issue was referenced by 7aaa7aa9dd

This issue was referenced by 7aaa7aa9dd79b8c6e37f351fd67a93ba07fbb883

Changed status from 'Open' to: 'Resolved'

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Changing the Alpha Mode of an Image in Cycles doesn't have expected effect. #53672