codediff.m

function d = codediff(fcc, conn)
%CODEDIFF Computes the first difference of a chain code.
%   D = CODEDIFF(FCC) computes the first difference of code, FCC. The
%   code FCC is treated as a circular sequence, so the last element
%   of D is the difference between the last and first elements of
%   FCC.  The input code is a 1-by-np vector.
%
%   The first difference is found by counting the number of direction
%   changes (in a counter-clockwise direction) that separate two
%   adjacent elements of the code.

sr = circshift(fcc, [0, -1]); % Shift input left by 1 location.
delta = sr - fcc;
d = delta;
I = find(delta < 0);

type = conn;
switch type
case 4 % Code is 4-connected
   d(I) = d(I) + 4;
case 8 % Code is 8-connected
   d(I) = d(I) + 8;
end