Quote Originally Posted by Bill McCrystyn View Post
I'm not sure why multiple passes seems to work so well - but it does.
There is a theoretical reason why it should work, in case you are interested. In Fourier series, all wave forms can be described by a set of sine waves. For example a square response, like the intensity profile of a building in an image would be made up of increasing frequency sine waves, and the higher the frequency used, the better the edge is represented.

In a blurred image, the edges are soft which corresponds to reduced intensity sine waves at high frequency. So when you do multiple sharpening steps, each with decreasing radius, it is like boosting those high frequency sine wave components in the Fourier Transform.

Here is an example of multiple passes I did in 2002:
http://www.clarkvision.com/imagedetail/unsharpmask
(obviously the statement about adding other images: I never got back to it).

Roger