Hi Nerdling. Its a little app called a "Spatial Filter". Its very hard to describe how it does it unless your into maths or engineering. Heres a post about it tho. PS/Gimp has some kind of similar ability but you will have to ask RobA how he does it with Gimp - I think its a extension for FFT's. See #12 and esp #15 of this thread...
Earlier you preformed a fix on a map I did to get rid of the 45 degree tilt caused by GIMP's cloud algorithm. I'm curious as to how you manage that.