CGTalk - how to define part of object as matte?

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gargle

11-07-2006, 06:06 PM

i have a plane with a set selection in the center that i would want to define as matte. It's basically a framed painting of which the center-part should be matte, in order to be able to put in videoclips later on. I know one can use the compositing tag to create a matte object but this makes the whole plane transparent, and not just the center part. Is it somehow possible to define the compositing tag to a selection, or even better would be if one could somehow create a matte material? because the plane at the moment has two materials assigned to it, it would be nice if one could just replace the old material with somekind of matte-material? I hope these dabblings make any sense to anyone. Any help is apprechiated!

cheerioz

govinda

11-07-2006, 06:14 PM

A matte material...the answer is in that part of your question. A matte material would just be all white for areas you want opaque and black for those you want transparent. So if you restrict a material to that part of your plane (you already have that part done) and put one of those colors in the luminance channel of a material it'll do what you want. Then in your compositing app you luma matte, inverse luma matte, silhouette luma or stencil luma, depending on what you want to accomplish. This question is more about compositing really.

Or, for another way, split off that part of an object and give it an object buffer with a compositing tag.

gargle

11-07-2006, 09:01 PM

thanks a lot govinda!
i'll go for the luminance channel and then make the alphas in ae.

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