I wonder how to do that in Blender. I desire to extract images of bump maps from normal maps, so that I can re-work them in Krita or any other painting software.
There are no built in method that converts a Normal map to a Bump in Blender. It would be possible to write a python script to do this but it would take much research to be able to produce desirable results.
I only know of one tool that can do this and that is Substance Designer.