GIMP Plugin Registry

A general purpose high-pass filter plugin. It shows up as Filters->Generic->High Pass Filter. You can select a blur radius that sets the size of detail to be passed by the filter, a contrast adjustment, as well as an option to keep the source layer or replace it.  read more »

Implement a highpass filter sharpening

Infos about highpass sharpening:
http://www.gimp.org/tutorials/Sketch_Effect/
http://www.retouchpro.com/forums/showthread.php?s=&threadid=3844&highlig...