Final gather swimming problem

[chagzuki]

I'm a novice when it comes to rendering, and new to these forums, so I'm hoping I can get some advice here.
I'm rendering a simple scene with 2 characters, a skydome, and not much else. Lighting is all from one HDRI, with just final gather, i.e. no light or photon emission. Whatever I do, whatever settings I tweak, I just can't get rid of a hideous amount of swimming in resulting images. I've set the antialiasing settings to 0 and 2, with contrast threshold at 0.025, and this is producing crisp outlines. However, even with final gather rays set to 4000 there's still so much variation from one frame to the next, it simply looks unnacceptable. Is there anything else I can tweak to resolve this, or is this a common issue with final gather and mental ray? The individual frames look fantastic, but once seen in sequence the anomalies are obvious. BTW, I'm only working at 768 x 576.

[chagzuki]

No replies. . .
Well, I've been demoing Turtle for the last 4 days, and it's a lot easier to get clean results with final gather, though it comes with it's own set of problems. I'm certainly getting better results overall with Turtle though.

[joojaa]

few quetions?

did you cache the fg solution? If you didnt then offcourse it will flicker. since it had no idea where the points for last frame ware taken from so it would generate new ones. Bacaus it didnt have the old ones it creates new ones that arent the same as proevious ones. NOt only that it will also make it faster.

Didi yoou attempt tho build future lookup caches, because it sure the hell will help. aling with making the solution faster to calc.

More isnt necceserily better here, what you shhould have done isnetad of turning the rays up is to adjust the sampling steps min max radius and filter size instead,

PS. turtle is a fg optimized renderer, so its faster on this accord but thenagain mr is so much more roboust on other fronts.

PPS and all this is explained in the mr manual (yes is ships with maya. ist jsut a bit hidden)

[chagzuki]

Thanks for your reply. Please excuse my ignorance regarding, well, a lot of things Maya and 3D. I'm doing a short college course at the moment and I've been trying to cram a whole load of information over the last 3 weeks, and there have been quite a few moments when I felt like my head was going to explode. But I'm eager to meet a deadline, so I'm prepared to suffer.
By cache you mean the part of render globals called 'Final Gather File'? I think this has always been left at the default setting, whatever that is.
When you say 'build future lookup caches', are you refering to the 'precompute photon lookup' option? I'm not using Global Illumination, so as far as I'm aware this won't have any effect.
Then there's 'final gather rebuild', which I think is to do with . . . now I'm getting mixed up with Turtle. Too much info!!!

Hang on, are you talking about the caching options for geometry, in the attribute editor? I've never had a clue what that's about.

[joojaa]

Yes i maen the cache file. One should realy realy use it!

Future lookup no i dont mean precompute foton, you need to do it manualy by rendering a few frames hhere and there in the timeline to generate a cache ofd points for even the points that are hidden in the first views render, Thisway whan mr buildts teh sample location it can opt to use the same sample point instead of a new one, even if its a sample point of the future (rays are still cast form that point but its still the same point, so one could expect the variance to be less)

[chagzuki]

It seems I had a final gather file specified as 'default.fgmap'
So you're saying that if I pre-render the frames that exhibit the most variation, and then re-render, the result will be much smoother?

Presumably, if any of the final gather settings are changed during this process, such as the number of final gather rays, then the whole thing is spoilt, unless one specifies a new final gather file?

What is object caching for (in node attributes)?

[chagzuki]

Also, will I disable the caching if I have 'final gather rebuild' enabled?

[chagzuki]

Isn't this technique for static objects only?

[joojaa]

Well static or no static the previous and fuure solution will help fg to optimize whether or notr to take a new sample point or not.

[chagzuki]

And would there be a great deal of difference between pre-rendering, say, every 20th frame and pre-rendering every 2nd? Is quality directly related to the amount of pre-rendered frames?
And is there away to compute the final gather points without actually rendering the whole frames?

[joojaa]

depends greatly on the animation. if thees much change then no amount of future lookup will help.

[chagzuki]

Wow, first tests show a world of difference using this technique. Most of the swimming has disappeared!

This is a massive step forward. Thank you.

There are still some odd artifacts, but I think they can be tuned out with the sample radius, or by increasing the FG rays. I hope so anyway, because besides those issues everything looks very nice indeed.

[joojaa]

your wellcome... its just that i not allways 100% free to do waht i want.