[RalphLambrecht]

Ralph,
Thanks for the link to the chapter. Very interesting reading.
I would not use the word "copy" in comparing the manual process to the filter in PS. Perhaps the idea is the same but the dig*tal world is a different story. Once you start getting close to the sampling resolution the damage to the data is significant.

Actually, the result may not be, but the underlying principle is exactly the same: increase edge contrast.