Cryptomattes ID types question

[Truffi]

Is there any documentation on the Cryptomatte's ID types "Node name with hierarchy" and "Node User Property" ? As I understand it, the first should seperate matte-groups by common hierarchy trees (in other words all objects that are linked together are grouped to one matte), the latter seperates them by a common attribute defined in the object properties.. correct?
Unfortunally I did not really get them to work in 3dsMax but would loved to - however I failed to find any indepth information about how to use both these modes in practice.
Is there a way to specify Cryptomatte groups simply by object IDs?

[hermit.crab]

You can read information about the VRayCryptomatte render element and its options in the technical documentation here:
https://docs.chaosgroup.com/display/...RayCryptomatte

Regarding your question - there isn't such an option (a pro of the cryptomatte is precisely skipping this step); you can use the 'node user property' mode and set the property in the user attributes of the object if you wish to include specific objects.

[Truffi]

I was asking because I did not understand how it "takes the node hierarchy into account for linked or grouped objects." In my tests using the ProEXR plugin inside After Effects grouped or parented objects were not sharing selection mattes in the render.

[vlado]

The hierarchy mode takes into account the full path from the scene root to the node when computing the Cryptomatte hashes and means that every object will get a unique hash, even for instances of the same object. In the regular node name mode, only the object name is considered and so all instances of an object get the same hash.

The Cryptomatte plugin for Nuke allows the use of wildcards so that portions of the hierarchy can be isolated, f.e. all objects with a given parent. I don't know if ProEXR allows you to do that. If not, then you can mark the objects you want to isolate with a custom node user attribute, and use that mode of the VRayCryptomatte render element. It's not the most convenient solution, but it can be a workaround.

Best regards,
Vlado

[Truffi]

Thanks for the answer. For me currently the most convenient way, that I got to work with ProEXR is the one seperating the masks via layers. If I understand correctly, the custom node user attribute allows only one seperation. That's why I was hoping there was a way to get it working with Object IDs as it would be even more perfect to organize (using the ID Tool script). Even the way it currently is, I definately appreciate the benefits of Cryptomattes over Multimattes!