Sharpening images with traditional methods increases the amount of
noise in the image.  This script implements a method to sharpen images
described by Joern Loviscach in the german computer magazine c't,
22/1999.

Basically it "squeezes" unsharp edges. This method is a simplified
Version of an algorithm by Nur Arad and Craig Gotsman: "Enhancement by
Image-Dependent Warping", IEEE Transactions on Image Processing, 1999,
Vol. 8, No. 8, S. 1063.