Cryptomatte: A few steps to make it work. Really easy.

1. Add the Cryptomatte Sub Pixel Filter to your render layer: Select the layer (Layer Editor) -> at the bottom in the Attribute Editor you can find the Sub Pixel Filters section. Add -> Cryptomatte
2. Open the Cryptomatte filter (Click on the small arrow), and set the type to AOVs and Manifest
   This way the Cryptomatte data will be stored as AOVs.
3. Done. 🙂 Render the Image via the Render Manager
4. Use as usual in NUKE with the help of the Cryptomatte node.

You can use the Cryptomatte plug-in in the non-commercial Nuke as well (it’s ideal for learning):

1. Download the Cryptomatte plug-in.
2. Unpack it
3. Open Nuke’s plug-in init.py file (for exmple: Program Files\Nuke12.0v2\plugins\init.py)
4. Paste this line at the end of the python script: nuke.pluginAddPath('D:/Downloads/Cryptomatte-master/nuke')
   Change the path of course, make sure you using / instead of \
5. Save the init.py file, restart Nuke.