Moore-Neighbor tracing algorithm

[YoungKnight337]

INPUT: A square tessellation, T, containing a connected component P of black cells.
OUTPUT: A sequence B (b1, b2, ..., bk) of boundary pixels i.e. the contour.
Define M(a) to be the Moore neighborhood of pixel a.
Let p denote the current boundary pixel.
Let c denote the current pixel under consideration i.e. c is in M(p).
Let b denote the backtrack of c (i.e. neighbor pixel of p that was previously tested)

BEGIN
Set B to be empty.
From bottom to top and left to right scan the cells of T until a black pixel, s, of P is found.
Insert s in B.
Set the current boundary point p to s i.e. p=s
Let b = the pixel from which s was entered during the image scan.
Set c to be the next clockwise pixel (from b) in M(p).
WHILE c not equal to s do
IF c is black
insert c in B
Let b = p
Let p = c
(backtrack: move the current pixel c to the pixel from which p was entered)
Let c = next clockwise pixel (from b) in M(p).
ELSE
(advance the current pixel c to the next clockwise pixel in M(p) and update backtrack)
Let b = c
Let c = next clockwise pixel (from b) in M(p).
END IF
END WHILE
End