Apologies this si more of the code:
G1 = 255 * mat2gray (I2 , [1 100]);
C2 = 0 * I2 (:,1)+1;
for i = 1:l
C2(i,1) = min ( G1(i,Xbp: Xep+3));
end
I2 is a 616x498 matrix
l = 616