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QMC GI creates odd light patterns on mildly complex objects

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Jareb CoupeQMC GI creates odd light patterns on mildly complex objects
by on May 10, 2015 at 12:56:18 pm
Last Edited By Jareb Coupe on May 10, 2015 at 1:13:47 pm

I had to bail on Irradiance Cache for a GI method (reasons described in different post), which of course leaves QMC.

I have noticed an issue in multiple scenes with QMC, and was wondering if anyone else experienced the same, or knew what the problem was.

Specifically, on objects with fine/sharp/deep angles, where the illumination is trying to reach a thin area, it does some odd shading. I can't tell if it's light that's not supposed to be there, or occlusion that's not supposed to be there.

Check out the pic:



I've also seen it occur with the default 'baseboards' with the new House Builder (NitroMan), as well as a the canned bed spread (Blanket 02) in the Visualize content.

I've tried:
- Removing Ambient Occlusion
- Removing all textures
- Reducing the scene to one light source (sun)
- Removing secondary GI method
- Increasing Accuracy of QMC to 90%
- Playing around with Discrete Area/Sky Sampling
- Simplifying extruded splines in hearth
- Other Phong options
- Other spline 'Type' and Intermediate Points settings

What am I missing?

Here's a version of the image with less compression.


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Jareb CoupeRe: QMC GI creates odd light patterns on mildly complex objects
by on May 10, 2015 at 1:11:51 pm

Something else worth mentioning: in lower light, the issue is accentuated. Also, I get the sense the pattern moves from render-to-render.



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Jareb CoupeRe: QMC GI creates odd light patterns on mildly complex objects
by on May 10, 2015 at 2:10:08 pm

And a shot of the baseboards I mentioned:



This may be a scale issue. I'm working in Inches, and a lot of these errors occur in the smaller/thin objects. Also, the pattern is a giveaway. Will investigate further.

Hobbyist level. Used C4D since R14. Now on R16.


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Adam TrachtenbergRe: QMC GI creates odd light patterns on mildly complex objects
by on May 10, 2015 at 3:53:08 pm

You'll probably need to increase the sample count. In the GI general tab, set samples to "custom sample count" and bump samples up until the artifacts start to clear up.


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