MATLAB: Find local differences in a matrix

Question

This is an image palette containing RGB value

cmap=

0  0  0
0.5019  0  0
0.7529  0.7529  0.752
0  0.5019  0.5019
1  0  0
0.5019  0.5019  0.50196
0  0  0.50196
1  1  1
1  1  0
0.5019  0.5019  0
0  0  0
0  0  0
0  0  0
0  0  0
0  0  0
0  0  0

calculate this formula

D(cmap)=cmap(x,y)- cmap(x,y-1)

Answer 1

D = diff(cmap,1,2);