Pat David has a great blog on photoediting in GIMP. I recently read his post on luminosity masks and was fairly impressed. Can darktable do something similar? Yes – they’re a special case of parametric masks.

I thought I’d post a quick tutorial on luminosity masks using parametric masks. First, I strongly suggest you read Pat David’s post and thoroughly understand what’s going on.

A quick and simplistic explanation follows: Normally, if we make a selection and, say, adjust the brightness dramatically in that selection, we get a sharp (and ugly) transition near the edge of the selection: