Tweet
I'm rendering people behind a glass railing and I want to matte out everything in the scene except for the people. So I select all people, invert selection, vray properties, check matte object, alpha contribution to -1, and check shadows and affect alpha. The render looks right, but the alpha doesn't include the transparent value of the glass. Just solid black. Also, I have a multimatte element for the people and the alpha isn't stored in that pass either. As a test I converted my glass to a max standard material with 50% opacity and the alphas are correct. Am I missing something? Thanks!
-
-
When Alpha Contribution is set to -1.0 it means that the transparency of the matte-object will cut out from the alpha of the objects behind, since the glass-materials are usually simulated via Refraction (not Opacity) the transparency is 0 which makes the alpha of the matte-objects completely black and it cuts out alpha-values for every objects behind it , in your case the object behind the glass will have clipped alpha.
When Alpha Contribution is set to 0.0 means the object will not appear in the alpha channel at all and will show the alpha of the objects behind it - in this case the transparency of the matte-objects is not taken into account and all the alpha of all the objects behind it will be rendered with their own transparency value, which means that the people behind the glass will not be clipped , but this doesn't apply for the MultiMatteElement.
Matte Properties works with transparency information not with Refraction one , that's why when you change Matte Object to Standard Material and use Opacity it gives you the result you are expecting - this works even with VrayMaterial if you use its Opacity Slot instead of Refraction Layer.
Comment