cycles bake artifacts with transparent textures and no color option
Closed, ResolvedPublic

Description

System Information
Operating system and graphics card
Windows7, Nvidia GTX 1060

Blender Version
Broken: 2.78a e8299c8
Worked: (optional)

Short description of error

trying to bake mixed shader with transparency with no color option generates too bright area.
non-100% transparency mixing or not transparent materials never generate these issues.
I use these techique for texturing, as seen in the file.

Exact steps for others to reproduce the error
example file:

open the file, DON'T change selection, hit bake.
for illustration attaching screenshots from this file

takateru (terubozu) updated the task description. (Show Details)
Sergey Sharybin (sergey) triaged this task as Confirmed priority.Feb 23 2017, 11:27 AM

@Dalai Felinto (dfelinto), is it something simple for you to have a quick look at? :)

I will look at it shortly. That said, I heard people complaining about lack of color management and baking. So it may be related

Hm this happens only with Path Tracing. If you switch to Branched Path Tracing it doesn't happen.

Attached the same file with a 1x1 baked image for quicker testing:

The final pixel has 1200 rgb.

@Sergey Sharybin (sergey) nothing seems wrong in the baking side of it (kernel_bake.h), and since it doesn't happen with branched path I suspect the problem is in Cycles itself. Shall we look at it together any time soon?

More debugging in case that helps:

The problem has a direct relation with the background plane (the big one underneath the one we are baking). If both objects have any color in the same channel we see the issue.

For example: the background plane has diffuse rgb(1,0,0), and the baked plane rgb(1,0,0) we see the problem. If they have rgb(1,0,0) and rgb(0,1,1) respectively we don't.

Assigning to @Sergey Sharybin (sergey), though who knows, maybe @Brecht Van Lommel (brecht) (friendly poke) has some time to wander around that instead. Or at least some clues to where to look at.

Fixed now, path tracing was baking transparent bounces which should not happen. Branched path already disabled it since it's handled differently for camera rays there.