Changing the Alpha Mode of an Image in Cycles doesn't have expected effect.
Open, ConfirmedPublic


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.


Philipp Oeser (lichtwerk) triaged this task as Normal priority.

I can confirm this behaviour and would also expect 'straight' alpha mode to not affect color data.
Maybe @Sergey Sharybin (sergey) can have a look?

Brecht Van Lommel (brecht) raised the priority of this task from Normal to Confirmed.Jan 3 2018, 12:36 AM
Brecht Van Lommel (brecht) claimed this task.

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.