From the script site "http://www.complang.tuwien.ac.at/schani/sharpblur/":
The purpose of this script is to blur an image while retaining its edges. While this may seem like a contradiction, it really is not: sharp edges get preserved while soft edges are discarded.
The main area of application for this script has been the retouching of bad scans, but it has many other areas of use.
Originally created by Mark Probst, Ported from 2.0 to 2.6 by Lennart Rolland.