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RenegadeRocks
11-03-2008, 11:12 AM
Hi guys,

I am using Mental Ray to render charactes for a movie project and have run into a peculiar problem.

I am using ray trace shadows with spotlights for lighting our characters. Usually the shadows comeout fine but:

On some of the characters I get strange artifacts with ray trace shadows. The transition from the lit area to the shadow area doesn't come out soft, instead I get crooked edges on the transition.Here's a image of the issue:
http://i38.tinypic.com/23hav5h.jpg


It effects only some meshes and not all. The face of the character in the above image was perfectly fine, but his cloth was givng this problem with shadows.
Here are my basic settings of this particular scene:


Using Maya 8.5
Renderer: MR
preset: Prodction
Raytrace: Enabled

Shadow rays 2 (default)

Light type: Spot Light
Shadows: Ray trace

Shadow Attributes:
Light Angle: 0.00 (default)
Shadow rays: 1 (default)

Anybody encountered this problem before?
Any clues will be appreciated ;)!
jeremybirn
11-03-2008, 02:26 PM
Just some ideas:

Is the shader a factor? Try this test: Assign a new PhongE shader (no textures or anything) to the object and render again. I'd be interested to see if the artifacts are showing up in areas where the light would be beyond it's terminator if the material weren't translucent.

Is the geometry a factor? If it were single-sided or only casting shadows from its back-face that might be a problem.

-jeremy
RenegadeRocks
11-05-2008, 06:12 AM
Hi Jeremy,
I have tried applying Lambert on it to check for Shader discrepencies, earlier too. The artifacts reduce on applying lambert but they don't dissappear.
http://i37.tinypic.com/ounqex.jpg
http://i38.tinypic.com/2hg4mqd.jpg
Also, the shader has no translucency or Incandescence value in it. Those were the parameters I checked for initially as I was thinking the same that whether the light has seeped beyond the transition from light to dark, but the shader has no maps or values in such parameters(Translucene, Incandescence or Ambient).

I checked the normals on your recommendation, they seem to be fine.

Also, one more character mesh has started showing the same issue now. Its on particular meshes, not on the whole character in both the cases and on rounded surfaces where the transition from light to dark is mostly visible.

Also, all the meshes have thier history deleted.

What bugs me is that it happens in some meshes and not on others, which is complicating the isolation of the problem.
jeremybirn
11-05-2008, 01:49 PM
Have you tried mesh clean-up to check for problems like multiple polygons sharing the same edges?

Is there a raytrace bias setting or anything especially huge/tiny about the scene scale in Maya unit size?

Have you tried exporting the selected model to a file, new scene, import just the model, and adding a light and rendering with fresh settings?

-jeremy
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