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GI Shadow Flicker (AGAIN!)

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Pravin Chottera
GI Shadow Flicker (AGAIN!)
on Jul 24, 2014 at 5:13:10 pm
Last Edited By Pravin Chottera on Jul 24, 2014 at 6:17:45 pm

I know there has been talk about this before, and I tried the tips in this post, but to no avail. I've tried using both IC+LM and QMC+LM, which both give me flickering, as well as QMC+RM but I lost all my light bounce. I'm assuming the solution in the above post didn't work for me because my scene looks quite different from the original poster of that post.

I'm basically lighting an entire scene with GI using polygon lights. And AO.

There are discs with a luminous material in the hanging lights and the back triangle wall is a giant light as well.

This is a still of the shot I'm rendering:

The flickering is worst in the background objects. I had my samples set to 200, and that cleaned up the flicker on on the left shelf, but I was still getting flicker in the details of the background objects. Raising my samples past 200 would lead to ridiculous render times, so I'm hoping there is something I'm missing.

These are close-ups of the flickering:

GI flicker 1

GI flicker 2

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Pravin Chottera
Re: GI Shadow Flicker (AGAIN!)
on Jul 24, 2014 at 7:29:50 pm

In case anyone is interested, I think I've figured out what settings to tweak.

I started with the preset "Interior - High (High Diffusion Depth)" which uses IC+LM. And the physical renderer.

I found the most important parameter to be Path Count under LM. I doubled the default (from 10,000 to 20,000) and that cleaned it up a lot.

I also changed the Record Density under IC from "Med" to "High". I used a custom Sample Count of 200 (under General) because I don't really understand the % increments. I find it more intuitive to use custom sample counts.

I also enabled "Build Radiosity Maps" under LM to improve render time. At least I've read that this setting improves render time. I want to experiment with it and see how much of an effect it has and if my system can handle it.

Finally I upped my AA from Med to High (just for funsies).

A 1280x240 frame it took me just under 2mins to render, which I think is great. The image is 98% flicker free!

My machine has a Cinebench score of 690, so I can afford using higher settings, but you could probably use lower AA and Record Density settings and get away with it. I'm creating video for a giant theater, so I need very clean renders, but for web video, I think this is amazing.

I'll post my renders in a bit, but I'd love to hear other people's experience working with the new R15 GI.

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Adam Trachtenberg
Re: GI Shadow Flicker (AGAIN!)
on Jul 24, 2014 at 7:51:33 pm

What sampling method did you finally choose? You have both camera and object animation in the scene? For your GI area lights (luminous polygons), do you have a material on them with the "GI Area Light" option checked in the illumination tab?

Off the bat I would use Cinema lights in the tube fixtures instead of luminous polygons.

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Pravin Chottera
Re: GI Shadow Flicker (AGAIN!)
on Jul 24, 2014 at 8:10:40 pm

I ended up using Irradiance Cache for primary (with a custom sample count of 200) and Light Mapping for secondary.

I had a very subtle camera push and very subtle object animation, so I want to test my current settings with more extreme animations.

Yes, I did have GI Area Light selected for all polygon lights.

You are absolutely right about the light fixtures. At first I had polygon lights, so no amount of sampling would get rid of the spotchyness (even in when rendering stills). But I used Cinema lights and it worked great.

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