Hey guys,
Im doing an animation and im trying to do the following. There’s an element that I need seperated from the rest of the scene, to have a matte mask in after effects to work with it. So im using cryptomatte to do get the images I need for the sequence. Just a basic black image with the object in white.
You might want to check out render passes, the FileOutput node in compositor and/or cryptomatte features which I believe should give you want you want (and more).
The MultiLayer OpenEXR file format might also be useful here.
These files were originally designed (by ILM …) to store lossless rendering output data for intermediate purposes. The “MultiLayer” extension was added by the Blender Foundation, and quickly adopted because it puts multiple named layers of data in a single file. It is intended to be "a file of numbers."