A sharpening effect I stumbled upon a bit by accident:

1) Duplicate the layer
2) Go to "Filters/Edge detect" and pickup an algorithm (almost all will do..., experiment!)
3) Find a suitable setting to extract important features (for difference of Gaussians, I used radii 3 & 1 for the image below)
4) Invert the result (black lines on white)
5) Put the "edges" layer in burn or multiply mode (burn often works better)
6) adjust opacity to taste

From what I understand this creates dark lines on the edges. Not too bad on plumages, and very nice on both sides of the screw:



Is it already known?

Nice one ofnuts.

Nice algorithm for sharpening. I don't believe i have ever seen it used before.It would be very easy to write a script for this also.

Coming up with sharpening techniques is a fun past-time ofnuts. Did BSSS a few years back. Mark turned my idea into a Script-fu.

Works excellent Graechan.
Thanks.