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SirRender
12-17-2003, 10:35 AM
Using Maya 5.0.1 on XP

I have some glass objects that I need to comp into an animated background in After Effects. I render my objects with my transparent alpha channel (opacity matte). No problem.

When I import and comp in AE (which I have done many times with renderings from other 3d programs), the transparent alpha is recognized but the alpha is not completely clean. Its as though some of black default background from Maya is not getting knocked out by the alpha.

Has anybody run it this problem when compositing transparent objects like glass into After Effects from Maya?

Can any body tell me how to just render out the transparent alpha of my object so I can use it as a track matte in AE. I uncheck rgb in the render global and only leave alpha channel check on, but I still get both. I just want the alpha channel frames. Any ideas?

Thanks for your help. I really need to make this work asap!
augustus
12-17-2003, 03:22 PM
It seems your images are premultiplied (basically not antialiased against background). There should be a way to say AE images are premultiplied. If there is not :argh: , you should render again, with premultiply option checked off, on the render globals window.
playmesumch00ns
12-17-2003, 04:10 PM
Don't know if after effects can do this, but the easiest way to fix it is to divide the image by its alpha channel.
SirRender
12-17-2003, 04:44 PM
It does seem as though Maya is premultiplying the alpha with the solid background a little, not completely otherwise I wouldn't have any transparency at all, but how do you turn it off in the render globals window in Maya? I don't see premultiply option anywhere.

How about just rendering out the alpha with no rgb. I uncheck rgb color from the render globals but it still renders. Any ideas?
augustus
12-17-2003, 06:47 PM
Originally posted by SirRender
It does seem as though Maya is premultiplying the alpha with the solid background a little, not completely otherwise I wouldn't have any transparency at all, but how do you turn it off in the render globals window in Maya? I don't see premultiply option anywhere.

Maya software: Render global settings->render options->color/compositing

Mental ray: Render global settings->framebuffer attributes
LennO
12-17-2003, 08:38 PM
In AE in the Interpret Footage Dialog there's an option called "premultiplied with color" and a field to chose the color from. If you have rendered against a black background, you shouldn't get any problems with that, and you'll have a clean masked object.

But if you know you're going to do stuff with your pic in post production always render with the appropriate options, as augustus told you.
Mananetwork
03-22-2004, 10:42 AM
I'm having the same problem, but when I do that in mental ray. Nothing happends. No difference!
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