A Computational Introduction to Digital Image Processing, 2nd Edition

356 A Computational Introduction to Digital Image Processing, Second Edition

2. Traverse the 3 × 3 neighborhood of the current pixel in an anticlockwise direction,

beginning the search at the pixel in direction

dir + 7 (mod 8) if dir is even

dir + 6 (mod 8) if

dir is odd

This simp ly sets the current direction to the first direction anticlockwise from

dir

:

dir 0 1 2 3 4 5 6 7

dir + 7 (mod 8) 7 0 1 2 3 4 5 6

dir + 6 (mod 8) 6 7 0 1 2 3 4 5

The first foreground pixel will be the new boundary element. Update

dir.

3. Stop when the current boundary element P

n

is equal to the second element P

1

and

the previous boundary pixel P

n−1

is equal to the first boundary element ...