Band-Limited Contrast

I want to compare the contrast of several images, for that purpose I need to measure the contrast. In fact I need the local contrast, not global. I already have a solution which just compares the neighboring pixel of each image pixe开发者_运维问答l. The results are ok, but now I need to compare it with another algorithm which I do not understand. It is mentioned in this paper from Peli: http://www.eri.harvard.edu/faculty/peli/papers/ContrastJOSA.pdf and is called "Band-Limited Contrast".

I understand it like this: Transfer an image to Frequency Space and there apply a low pas filter. Well. Apply another lp-filter with frequency range +1 next??? I really don't know what I have to do next... When I apply a lp-filter with range from 0 to 100 and another with 0 to 101 and then divide them and substract 1, the result is not what I had expected.

Does anybody know this kind of filter?

Thanks in advance Matthias