Strange gamma issue with textures

[SonyBoy]

We are well into a project and have suddenly had the same strange problem with file textures on two separate sets of shots. Textures that previously rendered correctly without gamma correction suddenly started requiring that gamma correction was applied.

So far as I understand it Vray is now completely linear, with gamma correction automatically applied to any textures that are not in linear color space. Am I wrong about this? And, either way, why should textures that rendered correctly without gamma correction suddenly need it? We are using Vray 3.06.04 with Maya 2018.2.

[Zdravko.Keremidchiev]

You said you have that issue again, where did you discuss the problem before? What format is the texture and is it only one particular texture that is using different gamma? Do you render animation and if yes, does the issue persist if you render the problematic frame alone?
Furthermore, V-Ray has always worked in linear space underneath and gamma is applied to the texture automatically depending on its extension. Can you set a simple scene with that texture to show the problem?

[SonyBoy]

I don't mean again, I mean we have the same issue on two separate projects. File format is 8-bit JPG, and yes there are other JPGs texturing the same scene that don't display the issue. We are rendering animation, and the problem occurs both on our render farm and into local workstation VFBs. So far as Vray always being linear, what I meant by this question was that at some point recently I think it became unnecessary to explicitly apply gamma correction to non linear textures? Not sure about this, but in any case we were not applying 2.2 gamma correction to those file texture nodes explicity -- until they suddenly started rendering incorrectly. The we applied it and got the correct results. Two separate artists experienced this independently. This seems very strange indeed.

[Morbid Angel]

Check if your color management settings have the gamma disabled. If its enabled then it might be gamma correcting texture by default.

[SonyBoy]

Color management is on, and I'm now realizing that on startup of Maya I'm getting an error message:

// Error: line 0: Error has occurred while loading color management policy file "T:/LIB/CG/TOOLS/MAYA/MAYA_ENV/ColorPolicy.xml" . //

Could this be the issue?

[Morbid Angel]

Could be - is that your pipeline path?

[SonyBoy]

Yep. Turned out to be this color management lookup file that some of our render nodes were unable to access for some reason. We pointed them all to local versions of the file and the problem went away.