PDA

View Full Version : rendering and compositing Glass (problems)??

Slimz
01-05-2006, 10:46 PM
hey,

i am doin a logo in maya and was rendering it using the dielectric material . It renders and looks great. but when it is time to composite and i import the file (or sequence) it on to the new background (using After effects), the alpha channel which i get is almost fully white.

In theory it makes perfect sense, glass is transparent so therefore no alpha. but i would like to render my image and have an alpha channel similar to if i had rendered the same object with lets say a lambert shader.

how do i render with the dielectric and get this type of alpha??
LehaS
01-06-2006, 02:34 PM
You mean with constant shading? try surface shader
Slimz
01-06-2006, 04:13 PM
what i mean is that when i use the dielectric material, when i render i seem to only get my alpha in like the highlights. the other parts are black. look at the image below.

i want to be able to composite the entire name. lets say on a different background. but as you can see the alpha will not allow that. is there a way for me to render the image so that i get an alpha similar to as if i had applied a lambert material and got a full cut out .

hope you understand
floze
01-06-2006, 04:59 PM
You only get alpha at areas actually occluded by some objects. The black part of it is when the refracted ray does not hit any other surface (like an environement ray). That's some attitude the dielectric has. Anyway. The alpha as you have it right now is quite useless if you want to composit it on a textured background. Maybe the 'semitransparent' alpha can be used if you had a constant color for background though.

Generally compositing refractions is quite tricky. Best solution is probably rendering out a separate refraction pass, similar to what you would do when doing a reflection pass. You then need a fully opaque alpha though.
orko60
01-15-2006, 01:37 PM
Why not make it Lambert or something, render it like that, and use that alpha on your nice dialectic render? I'm new to all this, but that sounds like the proper solution to me.
CGTalk Moderation
01-15-2006, 01:37 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.