Well if you don't have the Image Processing Toolbox, I'm afraid you won't be able to use blockproc. In that case, you would have to resort to something like this:
imout = zeros(size(im),class(im));
for m = 3 : size(im,1)-2
for n = 3 : size(im,2)-2
list = im(m-2:m+2,n-2:n+2);
imout(m,n) = median(list(:));
end
end
Note that this is the most naive way to do it. There are lots of better ways to do it, but this is the easiest to understand.
