In software such as GIMP or Krita one can obtain a wavelet decomposition of an image. What is the best way to use this decomposition to sharpen the image? I did a search of Google scholar for wavelet sharpening, but I could not find a good reference.
Some methods I have seen:
Duplicating the high frequency layers and editing opacity of the duplicate to taste.
Applying unsharp mask to each layer individually.
There’s a wavelet sharpen plug-in: https://github.com/gimp-plugins-justice/wavelet-sharpen/blob/master/src/wavelet.c
I can’t really tell what it is doing. I guess it is applying some variable weight on each level, essentially a more refined version of (1)?
Which one of these should give the best results? I suppose (3)? At best (2) is just crude edge detection, and if you just wanted to use USM on edges there are probably easier ways to do that.