Blue artifacts when motion blur is on

[renato_battaglia]

Hello guys,

I'm having some issues with my animations render, and I don't know how to solve them. 

I made an animation, and when I turn on the motion blur for final rendering, some weird blue artifacts appear on my rendered frames. These artifacts appear randomly during the animation.

Below some information:

Maya 2022

Arnold Render

23.976fps

I'm using an HDRI image on the skydome light (I've tried different HDRI as well)

Using some Arnold mesh lights and photometric lights for the headlights.

aiAtmosphereVolume for the fog

Basic Arnold shader applied to the truck

Default Arnold Sampling settings

EXR 32bit image format (tried different formats as well) 

Nvidia Denoiser

I've tried lots and lots of different things like adjusting the shader, increasing the render quality, increasing the lights samples, adjusting the render Sampling, etc., and nothing seems to work.

As this problem only appears when I turn on motion blur, I tried different motion blur settings, and nothing solves the problem either.

Other additional information: Other scenes with different truck models show the same behaviour.

If I was compositing on Nuke, I could just render the motion Vector and apply the motion Blur on the composition. But I'm compositing on After Effects, and I've never been able to get Arnold's motion vector to work properly in After Effects.

Does anyone have any tips on what may be happening, or maybe how to properly apply the Arnold motion Vector on After Effects?

Thank you,

Renato Battaglia

[Stephen.Blair]

Hi Renato

Blue is the NaN (not a number) error color.

I would check an Info-level Arnold log for errors.

Also, in what AOV do these blue pixel appear? Specular?

[renato_battaglia]

Hi Stephen,

Thank you for the information.

I enabled the info-level Arnold log, but I couldn't find any clues about the issue in the middle of so many information.

I ended up finding the problem by chance. It was some mesh lights that were creating the NaNs. After applying the cleanup and retopologize tools on those meshes and recreating the Mesh Light,  the issue is gone.

Best,

Renato Battaglia