fast SUSAN feature detection and non-linear filter

a fast implementation of the SUSAN feature detector by non-linear filter

This is a fast implementation of the SUSAN feature detection algorithm described at:

www.fmrib.ox.ac.uk/~steve/susan/

Also included is a general purpose non-linear filter based on the differences in intensities in a neighborhood. Any implementation of the SUSAN algroithm will require some kind of non-linear filter, so you may use this one if you don't have one already.

You will have to compile (this is what makes it fast) nlDiffFilter.f90 with mexf90.f90 to run everything else. I got some warnings from the compilaer about using the -fast option, but this hasn't been a problem.

You may try running demoSUSAN.m in debug mode to get a feel for how everything works.