1. Create a cryptomatte map in the Slate Material Editor.
  2. Drag the cryptomatte map onto a Map slot under AOV Shaders in the AOVs tab of the Render Setup window.
  3. Open the Arbitrary Output Variables window (AOVs tab of the Render Setup window).
  4. Select the Cryptomatte AOVs that you require and Add them (drag across to the right from the AOV List).
  5. Render the scene. The Cryptomatte AOVs should now be available in the AOV list in the RenderView window toolbar.

 

An example scene file can be downloaded here.