Artifacts in shadow pass

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  11 November 2005
Artifacts in shadow pass

I've had a search about, there seem to be a lot of threads about shadow passes, but none with the problem I'm having.

A seam is appearing along the threshold between the faces on the sphere that are and arent facing the light. Since a picture is worth a thousand words:

Beauty /\

Shadow \/

The best workaround I have found is to use depth map shadows and increase the bias a little, but this isnt ideal and doesnt work with raytraced shadows. Since it can render shadows fine in the beauty pass, where is it getting all this new information from, and more importantly how can I stop it?
  11 November 2005

What kind of light do u use for it? Do you use MR or Software?
  11 November 2005
Good points, I should have mentioned before.

I'm getting the same results with maya software, mental ray, depth maps, raytraced shadows, directional/spot lights, and any combination thereof. This leads me to think that the problems are with how I'm setting up the shadow pass, rather than incompatibility with anything else. Also, this is with Maya 7s new render pass features.
  11 November 2005
I've come across this problem a few times and it's been really annoying. Unfortunately I don't know what causes it but if anyone knows the answer I'd be interested to find out.
  11 November 2005
For the layer that's rendering the shadow pass, use a layer override to turn off primary visibility of the sphere, or at least turn off receive shadows. That way you just get the shadow on the ground.

Alternately, use another approach to setting up shadow passes, see this tutorial (pardon the pre-Maya 7 screenshot at the top, the rest still works.)

Jeremy Birn
Author, Digital Lighting & Rendering, 3rd Edition
  11 November 2005
Hereís my shadow pass technique. Iíve found that if I use a useBackground shader, with a matte opacity of .5 I get good results.
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File Type: jpg shadow_pass.jpg (72.6 KB, 48 views)

  11 November 2005
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