This page provides information on the Render ID Render Element which renders individual objects with different colors based on their internally assigned node handles.
The Render ID Render Element creates selection masks based on the node handle of each object or the V-Ray assigned render ID. In Maya, each object is internally assigned a unique node handle when the object is created. When V-Ray is rendering, each object is assigned a render ID. The intended use for the Render ID channel is to quickly create masks, based on the node handles or the render IDs, for various objects in a scene without having to set up a separate Multi Matte Render Element for them. A wide variation of colors is used so no two objects will have the same color in the render element.
Node handles and render IDs are not the same as the Object ID: The node handle is assigned by Maya (and can only be changed by Maya internally), and the render ID is assigned by V-Ray during rendering only. Meanwhile the Object ID is assigned by the user and can be changed at any time. In addition, while several objects can be assigned the same Object ID, each node handle and render ID are unique to a specific scene object.To create a channel that renders object colors based on Object IDs, use the Object ID (vrayRE_ObjectID) Render Element.
Node handle numbers do not ever change, even if objects are deleted; a node handle number for a deleted object is simply no longer used. Specific node handle values can be retrieved using MEL commands, but it is not necessary to do this to use the Render ID Render Element.
There is no anti-aliasing with the Render ID Render Element; where the edge of one object meets another object, the pixel color at that spot is the color from the object that contributes most to the pixel value.
UI Path: ||Render Settings window|| > Render Elements tab > Render 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.renderID.vrimg).
A common usage of this is to use the colors produced in the Render ID render element to create a mask or alpha channel in post production that covers everything with that Color. Another use is when you have a scene with many similar looking parts with similar shading and have the Render ID above this, desaturated of all color and set to an Overlay mode with a low opacity to add variation. A variation on this is to use the resulting desaturated Render ID render element as a luminance mask to then control color correction, etc.
The Beauty Render Element
The Render ID render element
The desaturated Render ID render element
The Final composite using the Render ID render element on top set to multiply at 21% to add subtle variation