This page gives information on the Render ID Render Element.
The Render ID Render Element creates selection masks based on the node handle of each object or the V-Ray assigned render ID.
In 3ds Max, 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 MultiMatte render element for them. A wide variation of colors is used so no two objects 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 3ds Max (and can only be changed by 3ds Max 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 (VRayObjectID) 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 MAXScript commands, but it is not necessary to do this to use the Render ID Render Element.
There is no antialiasing 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.
Note: The VRayWireColor render element produces results similar to that of VRayRenderID.
This render element is enabled through the Render Elements tab of the Render Setup window in 3ds Max and displays its parameters in a rollout at the bottom of the window:
VRayVFB – When enabled, the render element appears in the V-Ray Frame Buffer.
Deep output – Specifies whether to include this render element in deep images.
Use node handle – When enabled, uses the node handle from 3ds Max to choose the color instead of the Render ID (node ID).
Save XML report – When enabled, an XML file is created that includes RenderID, NodeHandle, NodeName and RGB value for each object in the scene. Such a report can be useful for interpreting the render element image.
XML file – Sets the location where the XML file is saved.
The VRayRenderID Render Element is useful for isolating geometry in a scene. This means that items can be isolated by use of a matte created from the solid colors within the VRayRenderID pass. Exact RGB values for any object in the scene can be looked up, if the XML report is saved. In the example, the leather ottoman is selected using the Render ID RE, and it is color corrected. See the render before and after compositing.