Rendering Reflections and Reflections Alpha

[Infrared digital]

Hi

I am trying to render the reflection of some CG characters who are walking on a reflective surface for compositing in Nuke.

So far I can get the reflections or the alpha but not both, does anyone know how to do this ?

I am also using a HDRi in a Dome light which I think is causing some problems but I cannot be sure.

Thanks

N

[Svetlozar Draganov]

Would it be possible to send us some examples so we could understand better what exactly you would like to achieve and what is actual setup?
Thank you very much in advance.

[Infrared digital]

Hi Svetlozar

Attached is a test render of some basic geometry on a reflective surface. What I want to do is to create an alpha channel of the reflections so that they can be isolated in Nuke.

Is this possible ?



Thanks

N

[Mokiki]

You can use the extra tex render element and use a vray dirt map inside.
There you can set its mode to "Reflection occlusion (Phong/Blinn/ward) + glossiness value" (GGX not available). Set the Radius to some pretty high number so all the objects get picked up. Use the Exlcude option to include just your ground. Oh and swap the black and white colors.
This method is not perfect but it'll probably get the job done.

[Infrared digital]

Perfect Oliver, thank you.

I had already tried that method but for some reason it didn't work - it works fine now !

[Mokiki]

Awesome

[pg1]

Extending this a bit further you also have to sort out shadows.

I use Render pass manager and do my shadows as a separate pass.
I usually do this inside of 1 max file using RPM but have split it out into 2 max files and zipped it so that you can have a look.

In the shadowcomp_Split_Beauty you can use the multimatte to separate the objects from reflection for grading
In the shadowcomp_Split_Shadow you can use the vray matte shadow element as a mask for a grade node and darken the background plate.

The shadow pass is rendered in red and green so that you can separate each shadow. I haven't done it in this file but often add an extra tex ambient occlusion for soft shadows.