Rendering Issues with Mental Ray

ksternschein · Apr 2013

Recently while I've been trying to render a scene with Mental Ray, I've noticed that whenever I stop the render, then continue from that point a little later on, the lighting seems to be different. While I haven't changed anything in the file, it still changes from the last rendered frame to the most recent. At first I thought it may be a result of a cache in 3DS max or something, but I later disabled that under the final gather render options. In addition to the lights changing, it seems like one light that is linked to a moving part isn't actually moving with the rest of the object, and so the glow from it stays behind. Below are two rendered frames, the first was done on one pass, then I paused the render, and continued later on (without changing the file), and there are significant differences in the shadows/lighting. Any ideas as to what this could be? I'm at a loss.

engelmanna · Apr 2013

I would guess it has to do with your Final Gather settings. You'll need to jack your FG quality up a bit to remove that flickering.

JohnnyRaptor · Apr 2013

Im thinking above poster is right and it could be your rays but you dont necessarily need to jack it up. I'm not too familiar with mr in max but look for the fg filter (default 0) and set it to 1 or at most 2.. This should clean up your splotchy ray hits.

ksternschein · Apr 2013

It isn't actually flickering. The problem is when I stop the render, then start it up again to continue from that spot. I was able to render about 20 something frames over one session. Then when I had it start rendering again, it looked as if the lights had moved. The lighting was consistent within the two sessions, but when played all the way through you could see the change

Fingus · Apr 2013

There's probably a random seed involved with the distribution of rays or samples.
Are you using Global Illumination? I'm not sure if it's the same in Max as Maya, but they look like the sorts of splotches you get from having a low number of photons.

ksternschein · Apr 2013

I had considered using global illumination to see if it would make a difference, perhaps keeping it more consistent. I'll give that a shot. Thanks!

Fingus · Apr 2013

I meant more that GI might be the source of the problem. I suppose it could also be a low amount of FG rays as well, I haven't touched MR in a while.

ksternschein · Apr 2013

I had a feeling it was a cache issue initially, but had already unchecked geometry cache. Low and behold, your mention of GI had me scroll down to that area and I found another area where it caches the FG rays. I'm running the render now and that may be it, looks good so far. I'll let everyone know if that's it.

ksternschein · Apr 2013

After sifting through more of the settings for final gather, I uncovered several more areas where there are options for various caches. The very last tab under the Indirect Illumination Tab is called Reuse (FG and GI Disk Caching). In this area there was an option to chose a mode that is suited for Walkthroughs/Stills and a mode for Animated Objects. My lights now seem to all render properly and don't change if I stop a render and pick it up again later. Thanks for the help everyone, definitely led me into the right settings!

Rendering Issues with Mental Ray

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