% create own histogram

I = imread('cameraman.bmp');
x = 0 : 255;
y = zeros(1, 256);

for i = 1 : 256
  for j = 1 : 256
    temp = I(i,j);
    y(temp+1) = y(temp+1) + 1;
  endfor
endfor

stem(x,y)
grid on
y