Render Elements/Multimatte: Selecting VDB clouds (VRay Volume Grid) for Post Changes...

[patrick_ortman]

Hello, is there a way to add VRay volume grid elements (such as my VDB clouds) to a multimatte render element? I want to be able to play with the look of these items in post (Nuke indie). If not, what would you suggest to do this task? I have also tried the Background render element, but that is literally just the Vray sky, with black cutouts where the clouds are. Thank you!

[Morbid Angel]

Hi Patrick,

There is only one way of doing this as far as I know. In the volume grid options you can set volumetric material ID color under rendering/volumetric. After that you can add materiaID RE to render elements. It will produce pure color of the volumetric in that output. You can use that pure color to isolate the given volumetric.
Keep in mind that volumetrics are not objects, so isolating them with pure color is limited, if they overlap each other with transparency it will be difficult to isolate and key them efficiently but this method at least gives you some form of control.

[patrick_ortman]

Thank you!

[cgdom]

The material ID does not seem to work with GPU rendering and volumes. (at least in v-ray v5.20.01)

[hermit.crab]

On GPU, you can work around it by setting the VolumeGrid mode to "Volumetric Geometry", adding an Object ID attribute to the grid, and outputting a MultiMatte element.

EDIT: Logged an improvement request for the material id (internal bug-tracker id: VGPU-5894).