CGTalk - Radiosity questions

Pate

03-19-2003, 04:59 AM

Hi!

I'm working on an animation, and I would very much like to use radiosity with it, but since I have moving lights and objects I can not use Single Radiosity Solution. Thus, I've been trying various tricks to speed up the rendering and get rid of the flicker. A couple of questions:

1) What is the effect of setting Prepass Size to None? The manual does not explain this, it just says to use Prepass Size 1/1 always for final rendering. As far as I have been able to determine, setting it to None has the effect of reducing the render time to half while not affecting the end result. Can this be correct?

2) Why is Stochastic Mode so horribly slow? I tried to render my scene with Stochastic mode. At first I set Accuracy to 10% and Stochastic Samples to 16, but after 2 hours C4D R8.1 had rendered only about 5% of the first frame. I stopped it, and set Stochastic Samples to 4, and after about 7 hours(!!) I got the first frame, which looked absolutely horrible. Is stochastic mode ever usable?

I have been getting reasonably good results with normal radiosity, Accuracy=70%, Stochastic Samples=400, Min=30 Max=150. Without antialiasing, rendering the scene takes about 15 minutes, and with 9xSMB I get a frame in every 2 hours with practically unnoticeable flicker. I still have ways to go with optimizing the material settings and render tags, but this looks like the way to go. (In case you are wondering, no, I have no deadlines :) )

Thanks!

Pate

STRAT

03-19-2003, 08:53 AM

1) a 0 prepass size will drastically lower image quality. try again and look closer. i usually use a prepass size for final images of 2 or 3.

2) Stoch mode rendering is horribly slow because it's full on proper gi. 100% accurate. even with the new addaptive gi rendering in 8.1 you still need a shit hot pc to make it usable.

3) those settings you mention are fine for stills, but to get the best non flicker animations you really need accuracy set to 100%, or use stoch mode rendering. I've used 99% (and even 98%) before now for animations, but even this noticably flickers. 70% for animation is absolutely hopeless.

ThirdEye

03-19-2003, 01:11 PM

Don't forget to switch on the 2 checkboxes at the end of the GI panel. "save solution" obviously, and "single animation solution" too, it reduces flickering dramatically.

Pate

03-19-2003, 03:02 PM

To ThirdEye_01: I was under the impression that Single Animation Solution is only usable when camera is the only element of the scene moving.. I have a stationary camera, practically everything else is moving, including most of the light sources.

To STRAT: Ok, I'll retry the prepass. Should the prepass image be full white except for the pixels that have a material that does not receive radiosity? I think it should be more like the images on MJV's radiosity tutorial page, with white dots scattered around the scene. Perhaps I have something wrong with my scene..

Also, have you used Scene Motion Blur? I think this reduces the flicker considerably. If I turn SMB off, I do get unacceptable flicker with accuracy at 70%.

I could try with accuracy at 98%, I just fear this would make the rendering too slow. My scene has about a million polygons and a dozen lights together with various transparent (with refraction) objects. Takes about 700MB of memory to render to 640x360 image. The problem is that I haven't even finished modeling the scene yet, I'm just doing some test renders to see if I need to remodel something before continuing. :)

Well, I guess I'll keep on testing various settings, thanks for the pointers guys!

Pate

ThirdEye

03-19-2003, 03:06 PM

Ooops sorry, if you have moving objects the only way to completely avoid flickerings is stochastic mode :hmm:

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