how to calculate distance transform using city block filter?

i am facing problem to calculate Distance transform of binary images using city block filter. I searched for that but failed.

2nd how can implement a filter without using builtin matlab filter functions. Please help and give me some examples to implement a filter without using builtin function. thanks.

Answer 1

[Walter Roberson]

1) http://www.mathworks.com/help/images/ref/bwdist.html

Example:

   MyMatrix = rand(19,42) < 0.5;     %some data for example purposes
   D = bwdist(MyMatrix, 'cityblock');

2) Read this

3) Look at the bottom of the above link. It says

For cityblock, chessboard, and quasi-Euclidean distance transforms, bwdist uses the two-pass, sequential scanning algorithm described in

[2] Rosenfeld, Azriel and John Pfaltz, "Sequential operations in digital picture processing," Journal of the Association for Computing Machinery, Vol. 13, No. 4, 1966, pp. 471-494.

[Muhammad Sohail]

Thanx Walter for replying. But what i was looking for, getting the distance transform without using bwdist function. what would be the process to implement city block filter manually without using builtin function. thanks

[Walter Roberson]

Use the two-pass, sequential scanning algorithm described in

[2] Rosenfeld, Azriel and John Pfaltz, "Sequential operations in digital picture processing," Journal of the Association for Computing Machinery, Vol. 13, No. 4, 1966, pp. 471-494.