The Material ID Render Element isolates objects with specific materials by Material ID for compositing purposes. This render element provides a mask for individual objects and materials that is easy to select in compositing software.
This render element either shows each material (by Material ID) as a solid unshaded color, or stores the Material IDs as integer values within the EXR format or VRay Image Format file. The Material ID for a material can be set in 3ds Max in the Material Editor.
The Color (with AA) method supports antialiasing at the edges of objects where they meet other objects or the background. The Integer (no AA) method, which assigns a Material ID to each pixel in the render element, does not support antialiasing as each pixel can have only a single Material ID assigned to it.
More than one VRayMtlID render element can be used if desired, for example if you wish to have both solid-shaded color and integer-based render elements for maximum flexibility during compositing.
