[ticket]

Here's a compositing problem I thought being solved a long time ago:

When using renderers like mental ray there's a way to render a straight RGB image meaning the Alpha channel won't be premultiplied with it. Using stuff like the UseBackground shader in Maya (I think it's called Matte/Shadow in 3DS Max) with this feature you won't run into problems during later composition of any layers. Since Maxwell has support for Matte Shadow and several Render channels I was wondering whether this would work, too. But it doesn't. Premultiplication always takes place. When rendering a separate Alpha channel this just bad and when there's a lot of DoF the composed results are horrible.

Any switch I missed? Help with that is greatly appreciated. Thanks.

[3dtrialpractice]

do a search.. for teh so called "alpha bug".. ppl talked alot about it..

I know TOM released a very handy Photoshop action on the maxwell THINK website that takes away the black and composits your image for you in foptoshop... you select the rendered image and then the background and run the action and it composits the two togetehr correctly for you.. this may help if i understand your question..

but there is no check like ther is in mental ray that will "overspray" the pixels in the render like mental ray does it..