Using PxrCryptomatte workflow, you can output IDs in Maya for easy selection in a compositing application. You can then use that selection as a mask to make changes selectively in post packages.

PxrCryptomatte is supplied as a Sample Filter plugin. As such the output for Cryptomatte is stored as a separate EXR file from your beauty or denoise outputs. Please note an OpenEXR is required to store the values correctly.

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The options above are default. You can find out more about the options by visiting the PxrCryptomatte page.

Note that after you create a Sample Filter, another empty connection will be created, allowing you to output Cryptomatte files using different criteria. For example, if you wanted one for per-object and another per-material, create another PxrCryptomatte for output and specify another name for the file.

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Below is an example in Nuke using our Robot Room Community Scene.

You can set a user string attribute in multiple ways if you want to assign an ID to geometry. Examples are as follows:

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When choosing identifier:object it will return the leaf level shape node.