Negative Colors In Rendered Image

[TheScope]

Hi,
lately we seem to get negative colors in rendered images quite often. Rerendering that frame / area usually solves this.
What could be the cause of this?

Cheers, Florian

[kosso_olli]

Does the error occur in 3dsMax or Maya?
We had this before with scenes coming from 3dsMax.

[TheScope]

In Maya. To be more precise: vrscene exported from Maya.

[Svetlozar Draganov]

This is most likely a bug with the software.
Can we get the Maya and .vrscene file exported from it for investigation?

[TheScope]

I can try to set up a scene that replicates the error since I can't send out this specific scene. In this case, the error was caused by one shader that was producing invalid values. Changing the shader resolved the problem here but ti was not obvious to me why the shader should produce such values.

I am investigating another scene right now.

[kosso_olli]

There are some situations which can cause this behavior. Often it is a default material or map in a scene that is not supported by V-Ray. A good habit is to assign a V-Ray material to all the objects in the scene, and no default materials. But I am sure that it the case for you already.

Further, in 3dsMax this could be a Falloff map in a shader set to shadow/light mode, or textures in lights with extreme values, especially gradient ramps. I actually posted a thread with similar name some time ago, but I don't know if it was fixed. The problem didn't happen for a long time now, though. Please keep in mind that these scenarios might be specific to 3dsMax, I have no idea if something similar could happen in Maya.

https://forums.chaosgroup.com/forum/...ection-channel

If you find the culprit, please report back here. Stuff like this is always good to know.

[TheScope]

In this case it was only Vray shaders in the scene but the render error only seems to pop up in certain situations. I did not yet succeed in replicating the error with this shader in a more simple scene. Lighting was just a Vray sun and a Vray dome light with an HDRI.
I tested some other things to solve the problem, some of them produced less render errors but only replacing the shader did get rid of the warning message an all render errors.
Things I tried:

• clamp the black values of the HDRI ( I suspected some negative values from editing the HDRI)
• Use brute force only GI instead of BF / LC
• Higher LC settings
• Clamp output set to 10 (instead of off)

[vlado]

We will really need the scene to see what's going on.

Best regards,
Vlado