Speed up the code

I want to speed up the code(replace the for loop) for checking whether the pixel at the center of the 3x3 neighbourhood is a minima or not. Can anyone help me with that.

function [critical_map] = Make_Critical_Map(gray_image)

[rows cols] = size(gray_image);

critical_map = zeros(rows,cols);

for i = 1:rows

      for j = 1:cols
          test = true;
          %Check whether the gray value is lowest in the 3x3 neighbourhood
          for row_inc = -1:1
              if(test == true)
                  for col_inc = -1:1
                      if(test == true)
                          if ((i+row_inc)>=1) && ((i+row_inc)<=rows) && ((j+col_inc)>=1) && ((j+col_inc)<=cols) && (gray_image(i+row_inc,j+col_inc)<gray_image(i,j))
                          test = false; 
                          end
                      end
                  end
              end
          end

         critical_map(i,j) = test;
     end
  end

Answer 1

[Friedrich]

Hi,

do you have access to the Image Processing toolbox? If so, you can use the imregionalmin function:

http://www.mathworks.com/help/releases/R2011b/toolbox/images/ref/imregionalmin.html

 A = randint(10,10,[0 255])
 BW = imregionalmin(A,ones(3))

[Saurabh]

Thanks!

Answer 2

[Sean de Wolski]

Using colfilt():

I = magic(5);

Imin = colfilt(padarray(I,[1 1],inf),[3 3],'sliding',@(x)(min(x,[],1)==x(5,:)));
Imin = Imin(2:end-1,2:end-1);

[Saurabh]

Thanks!