minObjectID

minObjectID 1.0

Type: Shaders

Updated: June 19, 2009

Availability: Released

Compatibility

Host Applications: mental ray

Operating Systems: Windows, Mac OS X and Linux

Architecture: 32-bit and 64-bit

Overview

This lens shader assigns each object in a scene a distinct, randomly selected color, the so called Object ID.

An Object ID pass isn’t exactly pretty, but it is incredibly useful because a compositing artist can apply effects or corrections to individual objects or specific areas without the need to render separate masks or even paint masks by hand.
My approach to this shader is somewhat naïve in that it randomly assigns a color to each object without regard for adjacent object’s colors or possible repetitions. However, the chances of the same color being picked twice by the algorithm are so small as to be negligible for all intents and purposes.

Usage

Once minObjectID is assigned to your objects just hit render and you’ll have a random color on each and every object — no need to manually specify object- or label IDs.

Note that this shader’s output is not compatible with Nuke’s or Fusion’s ObjectID format as it does not save to an integer buffer in OpenEXR files.