Black spots and "swimming" artifacts in animation with "Animation (prepass)" mode

[Alex_M]

I'm trying to render a simple 600 frame animation with one moving object (sliding roof) and a slowly rotating camera. The roof opens slowly throughout this animation. Because of the moving object, according to the help files I need to use the "Animation (prepass)" method, correct? I read the whole tutorial and tried it in my scene but the results are very bad - there are flickering black spots and swimming artifacts everywhere. Why is this? Is it because I've rendered the irradiance maps through Backburner on multiple machines (I've used 4 machines)? All Vray and Max versions are the same across all machines (check my signature for version info) and there are no special plug-ins used in the scene. Just simple light setup (sun + dome) and clay material on all objects.

Below you can find a rendered frame from the animation with the "animation (prepass)" mode. Attached is also a part from the rendered animation. This is a bit urgent so any help is appreciated.

[piotrus3333]

I go with brute force nowadays for interior animations. and light cache in fly through mode, 4000 samples should be enough for 600 frames but check that on small animation sample.

[super gnu]

yes, animation (prepass) imap is rather hard to get working right, and by the time youve done all the imap calcs, and set the interpolation frames high enough to stabilise it ( each extra frame blended bumps up the rendertime) you are close to the time needed for a lovely clean BF/LC solution.

if you re on 3.3, just stick vray on default, switch to adaptive aa, turn LC retrace up to 6 or 8 and set the lc subdivs a bit higher (say 2k) and you should be good to go for an animation with moving geometry.

id not use LC in flythrough mode.. that is for static scenes.

[Syclone1]

Im wondering if it could also be overlapping faces, I would change your "Secondary rays bias" under global switches to something like 0.001 Sometimes for me that helps black spots like that.

[Alex_M]

Thanks for the replies. No overlapping geometry. I might give BF+LC a go. Indeed I could have rendered that thing by now instead of wasting my time trying to make prepass work.

[Alex_M]

Hmm... That won't go very smooth. It takes 5 minutes to compute 1 frame with all 4 machines if I use BF + precalculated LC. That would be 50 hours of render time. Any other suggestions? Maybe there's something I'm missing with the prepass method to make it work properly?

[piotrus3333]

turning off retrace for LC will speed things up. or set it to 1.

[super gnu]

turning down or off retrace can lead to blotchiness in the gi that changes every frame. you may get away with it..

to be honest interior scenes with animated GI always take ages to render. the new 3.3 settings and improvements to BF have taken it from " impractical if you are not pixar" to "fine for a medium sized studio if used sparingly" 20 mins on one machine is pretty fast for what you are asking.. if you plan to do stuff that is compute intensive you need to plan for it and have the horsepower available. 4 machines wont cut it. (having said that, a 50 hour rendertime for a 600 frame sequence is what i would call "expected" its a weekend and a bit. or a fistful of dollars on a renderfarm.

you will either have to work on getting the imap solution to work (but its not much faster in the end) or go old school and use lights instead of GI. you can also go halfway here by getting as much direct lighting in there as possible, meaning the gi has to do less work. this will speed things up.

[super gnu]

you should also not be using precalculated lightcache.. calculate a fresh one with each frame, otherwise your secondary bounces will be static and your first bounce not. which is... not right.

[Alex_M]

Sorry, I didn't articulate right. I meant to say that LC was computed when I rendered the irradiance map in prepass mode. After that I turned off the secondary GI engine as suggested in the official tutorial. So that shouldn't be the issue I think.

you should also not be using precalculated lightcache.. calculate a fresh one with each frame, otherwise your secondary bounces will be static and your first bounce not. which is... not right.

[super gnu]

i was referring to when you said "all 4 machines if I use BF + precalculated LC."

in this case you should not use a precalculted LC. however if you just mean it was calculated before rendering starts.. then.. end of misunderstanding

[Alex_M]

I tried to complete the official tutorial on the prepass method (I also modified it a bit by animating the sun position too). The results are not good. Below are 2 identical frames. The better looking one is calculated in single frame mode and the other one (the worse) is done with the prepass method. Why is the result with prepass so bad? And this scene isn't even a complex one. Changing interp. frames from 2 to 5 but didn't help.



Here's also a screenshot of the irradiance map viewer tool. These are two identical frames side by side. Same irradiance map settings. Only difference is that one was rendered in prepass mode and the other in single frame mode. Why is there more definition (especially in the shadowed area under the ball) in the single frame mode? Could this be the problem? What should I do to make the prepass mode produce the same quality as single frame mode?

[Zdravko.Keremidchiev]

I tested this same scene and I get very similar result with both Single and Animation (rendering) modes. Could you please check again how did you render the single pass node? Could you attach a screenshot with the settings that you used?
In here even the Irradiance maps look the same.

[Alex_M]

I'll check this and let you know. Did you also animate the sun in the test scene? I did in mine. Can this animated light cause the issue? By the way, I spent some time yesterday and created a new light setup for the interior animation such as that it fakes GI and I sent it to BB for rendering. Looks as good as real GI but faster and without any splotches or artifacts (see snapshot below). I couldn't be more happy with the result.