What is post-processing masks?

README mentions needing *optional* dependencies for stuff like *"post-processing"*. What is post-processing masks? It's mentioned no where else in the README or examples, so hard to tell if it's something I would need.

Start with the README passage that mentions optional dependencies and post-processing, then check the repository's example notebooks for any related mask-processing usage. Done means the README explains what post-processing masks refers to and whether a user needs the optional dependencies, with wording consistent with the examples.

Written by the indexing model from the issue text.