Help me vectorizing this code

I dont quite get the vectorizing way of thinking of matlab, mostly due to the simple examples provided in the documentation, and i hope someone can help me understand it a little better.

So, what i'm trying to accomplish is to take a sample of NxN from a matrix of ncols x nrows x ielements and compute the average for each ielement and store the maximum of the averages. Using for loops, the code would look like this:

for x = 1+margin : nrows-margin
    for y = 1+margin : ncols-margin

        for i=1:ielem
           % take a NxN sample 
           sample = input_matrix(y-margin:y+margin,x-margin:x+margin,i)
           % compute the average of all elements
           result(i) = mean2(sample);
        end %for i

      % store the max of the computed averages
      output_matrix(y,x)=max(result);

      end %for y
  end %for x

can anyone do a good vectorization of this example of a situation ? Thank you in advance for any input :)