The Render ID Render Element creates selection masks based on IDs automatically assigned by V-Ray during rendering to all objects in the scene. Each object is assigned a unique integer number and each number is colored differently. The intended use for the Render ID channel is to quickly create masks for all objects in a scene without having to set up separate Multi Matte Render Elements. The masks can be separated by their integer values or by the color used to represent them in compositing applications. A wide variation of colors is used so no two objects will have the same color in the 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. The Coverage Render Element can be multiplied by the Render ID Rrender Element in compositing to add anti-aliasing to the Render ID.
Render IDs are not the same as Object IDs: the render ID is automatically assigned by V-Ray during rendering only, while Object IDs are assigned by the user and can be changed at any time. In addition, while several objects can be assigned the same Object ID, each render ID is 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.
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UI Path: ||Display Render Settings button|| > Render Elements tab > Render ID
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To use render elements, select from the Available render elements column and click the Add button to add the passes you wish to generate at render time. When you render the scene, the added render elements listed in the column on the right, will also render, which can be viewed from the VFB window's channel drop-down menu.
For more information on the parameters on this dialog, see the Render Elements tab page.
