AOV for shadows/reflections on matte objects?

[kai_wheatley]

I am rendering CG for a live action plate and I've got a scene full of matte objects. The main CG is being rendered over a reflective table, which I have created a matte object to match the real object. I have gone through most(I think all, but maybe I'm missing something without realizing) of the AOV's (related to shadows/reflections) and it seems like none of them will give me anything on the matte objects. For example, the VrayRawReflection only gives me the reflection on my non-matte objects. The same goes for all of the shadow passes. They give me the shadows on the non-matte objects, but nothing on the matte object itself.

I can't get my shadows/reflection to my liking via the render and I would like to be able to darken them in Nuke. I've done a hack-job way that allows me to darken the plate in those areas, the issue is, I need the reflections to be darker but the shadows to remain the same, but I can only darken/lighten them together (the shadows and the reflection).

Why don't any of the AOV's for shadow OR reflection show me anything on the matte objects? Is there a way to get the AOV's to work there? (and just to be clear, there IS a shadow AND a reflection in the render that is contained in the alpha channel of the render, but I have no way of controlling them individually).

Thanks for your help

[Joelaff]

We render the shadow and the reflection matte objects as separate render passes using state sets.

[vladimir_krastev]

Hi, thanks for posting. If you want to use render elements over the matte object you have to render twice. You could use the alpha from the matte pass as a mask.
In my test there is a plane and a box with reflective material. With these settings for the plane (the matte surface):


You'll get this for the Alpha and RGB


This Alpha could be used as a mask to adjust only the reflections that are over the plane.