CryptoMatte Node and Port Filtering
In order to write an EXR file with CryptoMatte information, it is necessary to add Port Names to the outputs of the desired image nodes in the scene. When Port Names are applied, the CryptoMatte-Write Node will find all the Port Names connected to the rightmost port and create an appropriate matte and ID in the CryptoMatte output as necessary.
NOTE Due to the CryptoMatte-Write Node searching up the Port Filtering Chain, it is not necessary to apply Port Filters for the exporting process. Only Port Names are required.
The CryptoMatte-Write Node will only progress as far as the first named port. If nodes with Port Names are contained in a group that also has a Port Name assigned to it, the Port Name of the group will override those contained inside. The individually named layers contained in the group will not be separated on export as a result. You cannot have two passes with the same name owning the same pixels.
NOTE For more information on Port Names, see Port Names.