View Full Version : Renderman for Maya alpha edges problem

07 July 2009, 06:35 AM
We're using Renderman for Maya 2.0 and are getting some serious edge mismatch problem.

there are 2 problems here:

1) Please refer to image A, (a composite in Photoshop). The cliff and the ground are 2 separate passes.
There is a thin line between the Mountain and ground, where the alpha is missing - its like a 1 pixel wide gap. I've tried premultiplied interpretation with black in After Effects, also tried the 'black matting' option in photoshop, etc. but with no results.

2) Please refer to image B, (a still jpeg conversion of the Maya IFF output) - its a simple RGB matte. You can see some strange dark outlines around objects where the red intersects the green. It seems the intersections are taking the median color between red and green.

How do I get the alphas to match? is there some kind of render setting? And how do I get rid of this intersection color problem?

thanks in advance!

07 July 2009, 10:05 AM
In fusion I was able to solve these kinds of problems before. I am not sure about how to do that in AE though.

07 July 2009, 03:24 PM
At first glance I thought it was a problem with the alpha as well, but if you're saying you've already tried pre-multiplying the alpha in post, then I'm not sure what's wrong.

I haven't experienced this with RMS, so it might not be software related.

Can you reproduce this in a simple test scene and upload it?

Have you tried posting this in the pixar forums?

07 July 2009, 03:25 PM
Hey guys,
I forgot to post the other image:

I'll post to the pixar forums. And I'll send a sample maya file as well.... Thanks :)

07 July 2009, 03:28 PM
We've tried Nuke, AE, Fusion, Photoshop, but the problem still persists. It's only when we use a matte object that we get these lines. (tried with both matte object and black hole).
For example, the rocks were rendered separately at first, with the ground as a matte object. there were lines around the rocks.
could it be something to do with the matte shader? or something in the render settings? we are using separable catmull-rom for AA. Perhaps we should adjust the settings for AA?

As for the red and green overlapping, cant figure it out. green and blue adjacent to each other is fine, just not red...

CGTalk Moderation
07 July 2009, 03:28 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.