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render error (flicker) in highlights when rendering with mental ray

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David Matthies
render error (flicker) in highlights when rendering with mental ray
on Oct 26, 2010 at 3:57:39 am

I am somewhat new to MAYA, there is a flicker in the highlights when I render with mental ray. Here is the render:

http://cowboymustache.com/texttest1comp.mov

Does anybody have any suggestions? All of the text objects are rigid bodies. The word "TRUTH" has gravity applied which I applied by setting the rigidsolver start time to frame 150. After the collision occurs, I keyframed the magnitude of another instance of a gravity field on the rest of the text objects so they did not fly off into space. When I watch the simulation in Maya, the text objects fall the same way every time. When I render it out, the fall and collisions are different every time. I am also getting error messages in Maya that there are rigid body interpenetrations, but I have quadruple checked that there are no interpenetrations before the collapse starts and the error messages don't start until I play through the collapse in Maya. All of the objects are shaded with a basic blinn material with the diffuse set to 100. Please let me know if there is any other pertinent information that might be causing the problem.

I rendered out one version with the maya software render with no shadows, and the flicker was not there. I am rendering out one right now with shadows, which is taking about 5 times as long as the mental ray render did, but from the still frames, it doesnt seem to be there.

Thanks in advance for the help..

Dave Matthies
Cowboy Mustache


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Michael Frank
Re: render error (flicker) in highlights when rendering with mental ray
on Oct 26, 2010 at 7:51:12 pm

Are you working with Final Gathering? Without really high sample rates FG will flicker across animation frames.

Mike Frank
Cave House Studios


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David Matthies
Re: render error (flicker) in highlights when rendering with mental ray
on Oct 26, 2010 at 8:05:34 pm

Thanks, I researched the issue and found out it had to do with Final Gather on another site. Do you have any good resources to recommend about the particulars of Final Gather (in addition to the excellent MAYA documentation)?

I noticed that final gather also adds quite a bit of light to the scene, is there a way to counteract this in the FG settings, or do I have to lower the intensity of the lights?

Thanks!

Dave Matthies
Cowboy Mustache


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Michael Frank
Re: render error (flicker) in highlights when rendering with mental ray
on Oct 27, 2010 at 2:16:49 pm

Final Gather is still kind of experimental to me. The reason why the light is increasing is because the light is bouncing off of neighboring surfaces. That radiosity look is what makes it feel so natural and "real". There is a slider in the FG settings called FG Diffuse Scale - I believe that influences the strength of the bounced light. You may still need to tweak the light intensities.

Recently worked on a project which involved FG.. we really didn't have a lot of render time to spend, but we wanted to get that realistic look to the lighting. My render guy came up with a really nice solution which saved us - we used a Motion Vector 2d pass and did a mo-blur in post over top of the final render. As long as we had kind of a moving camera the FG quality settings could remain really low, as the noisy areas would typically have the motion blur smooth it all out.

From what I've heard though - If you're working on an animated sequence the best way to go is to learn your way around using Global Illumination instead of FG. Unless you want to throw down and get a render farm so you can increase the FG samples.

One other idea I've had would be to render your Final Gathering results as a separate pass and run noise filters to clean up the noisy areas. Haven't had the chance to test that yet.

Mike Frank
Cave House Studios


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