The Multi Matte ID Render Element isolates objects with specific Multi Matte IDs for compositing purposes.
||Render Settings window|| > Render Elements tab > Multi Matte ID
The parameters for this render element appear in the Attribute Editor under Extra V-Ray Attributes.
Enabled – When enabled, the render element appears in the V-Ray frame buffer.
Deep output – Specifies whether to include this render element in deep images.
Filename suffix – The text added to the end of the rendered file, when saved as a separate file (e.g. myrender.multimatteID.vrimg).
This render element is not supported with V-Ray GPU rendering.
Here's the workflow for setting up and using the Multi Matte ID Render Element:
Select the material in the Hypershade that a Multi Matte ID Render Element is needed for.
Add the Material ID attribute Attributes > VRay > Material ID.
Set the Multi Matte ID to the required value. Note: each number corresponds to a different color.
Open Render Settings and go to the Render Elements tab and from the Available render elements add a Multi Matte ID render element.
A typical usage of this render element, is to use the colors produced in the Multi Matte ID to produce a mask or alpha channel in post production that covers everything with that Multi Matte ID.