3 Layer Composite question (2)

[ryan-saper]

I am trying to create a scene with 3 layers total (at least so far). I have a matt painting, myself on a green screen, and on the top composite layer I have another 3D object in Maya which I need to interact with. I need to know if there is a way for me to render my object with mental ray (physical sun/sky is being used) but have the background completely lime green so I can keep the lit object, but the actual background be keyed out later. I know in 3Ds max i could set the environment background to any color i wish, however, a green environment will effect the way my object is lit. Is there a way to do what I want in maya? So my main points are:

1) a lit animated object from Physical sun in mental ray
2) create a green background for chroma key

I think I could render it in passes and only use the object, but I dont know how to do that or if it would even work. Please help. Project deadline in 2 weeks.

[joojaa]

You don't need the green background. The 3d image comes with a alpha channel that does the same but automatically and without any keying artefacts. Just choose a alpha enabled format and drop it into your virdo application background should now be transparent (that is if not then your video application dont work like all the 90% of others in wich case you need to consult the manual on alpha use).

If you need extra elements like shadows then use use background on teh cast to surfaces theese will automatically create mattes for the composite.