Neighborhood processing with nlfilter

I'm attempting to isolate the 4-neighborhood for processing while using the nlfilter. I can isolate the 8-neighbors by simply using a kernel size of 3x3, but is there a way I can write a function to further isolate the 4-neighbors and then do my processing. Thank you in advance for your help.

Answer 1

[Image Analyst]

It gives you a n by m subimage. What you choose to do with that is up to you. You can ignore the diagonal elements if you want - just simply don't use them in your algorithm.