Ambient occlusion dropping buckets

[cimprichjb]

Hello, I'm having a slight issue with rendering high resolution ambient occlusion passes in 3dStudio Max. I'm rendering 2700x1700 and when I render with occlusion, It will skip over spots and leave squares of black that did not get rendered. At a lower resolution, the render works fine. My material samples are at 256, distance at 1.0 and spread at 20. The rest are at defaults. It renders most of it just fine, leaving 5-10% of it unrendered. This doesn't sound like a material issue, but more like a hardware (memory) or render settings problem. If you have any ideas of how to resolve this it would be much appreciated.

Thank you.

 

Also can a mod please move this to the mental ray forum please?

Edited August 20, 2008 by cimprichjb

[LukeC]

Do you happen to have an example image? Just to help me understand a bit better

[cimprichjb]

can do! The original render is 2700x1700. I downsized it to 512 for the forums. Any ideas? keep in mind that it renders fine in lower resolutions

 

[SandmanNinja]

Send me the file - I'll see if it works on my machine.

 

Have you tried lower samples, different resolutions, different distance and spread?

 

What are your machine stats? i.e. ram, OS, etc?

[cimprichjb]

For a few reasons I can't send you the file, but I believe I tried tweaking the samples. The computer has a quad core processor (2.54 I think), and 4 gigs of ram in it. Seems random though as it rendered fine this morning, but then did it again when i tried to render an interior.

[mattclinch]

its your frame buffer running out of RAM. check here for solutions - http://www.cgarchitect.com/vb/30970-black-artifacts-when-using-final-gather-map.html

 

also.. 256 seems like a very high number for AO samples... 64 - 128 tops.

[cimprichjb]

Thanks Matt! I'll give those suggestions a shot