Zone System Separator might be worth a look. This script creates layer masks based on the Zone system (eleven tonal ranges) photography technique by Ansel Adams and Fred R. Archer.

wow Odinbc, you are a genius !
thank you

how did you come up with looking for this technique ?

I've known about Ansel Adams for many years he's a bit of legend in Photography. The Zone system is for photographers so the script is more an illustration. I was at the Registry one day and noticed Zone System Separator with Ansel Adams mentioned and when I tried it out I thought the masking might be useful. I haven't taken advantage of it yet but I can see the potential.

BTW, Did you find the German link, with some background, at the Registry?

yes !