This may fit into my never ending G'MIC exercises thread but I have decided to make a new one. Came across Kovesi’s site yesterday which has lots of interesting goodies. His GitHub has examples.
In particular, I have been interested in ways to overcome
gradient_norm's weakness of doubling thin features such as the whiskers of the
tiger and variable feature outline thickness and brightness. Observe:
Comparison using his sample images (left);
gmic), phase congruency (right, older faster version).
Perceptual colour maps are interesting as well. Reminds me of my Palette to clut to application thread among other related discussions.