I have often wanted to turn a normal map into a displacement map. Of course, simply turning it into a greyscale is not the way to go.
Actually, I don't understand how a displacement map can be derived from a normal map. They are describing very different things. The normal map describes the "real" angle of a surface relative to the actual value whereas a displacement map is a perpendicular (clue is in the name!) displacement relative to the surface.
How can one derive one from the other?
(please excuse my non-technical language)