I have this kind of matrix (13 x 13):
0 0 0 0 0 0 0 0 0 0 0 0 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 0 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 0 0 0 0 0 0 0 0 0 0 0 0
Can I somehow increase the values around the central zero and the zeros that make the "walls" by one at each iteration and make it as this?
0 0 0 0 0 0 0 0 0 0 0 0 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 1 2 2 2 2 2 2 2 2 2 1 0
0 1 2 3 3 3 3 3 3 3 2 1 0
0 1 2 3 2 2 2 2 2 3 2 1 0
0 1 2 3 2 1 1 1 2 3 2 1 0
0 1 2 3 2 1 0 1 2 3 2 1 0
0 1 2 3 2 1 1 1 2 3 2 1 0
0 1 2 3 2 2 2 2 2 3 2 1 0
0 1 2 3 3 3 3 3 3 3 2 1 0
0 1 2 2 2 2 2 2 2 2 2 1 0
0 1 1 1 1 1 1 1 1 1 1 1 0
0 0 0 0 0 0 0 0 0 0 0 0 0
If you have the image processing toolbox, it's a one-liner:
%# assume your matrix is called A
result = bwdist(~A,'cityblock')
'result' is the distance of each non-zero pixel in A to the nearest zero if you can only step horizontally or vertically.