Freeman chain code with first differences and shape number

% CC = FREEMANCC(B) computes the 8-connected Freeman code, the first
% difference of the chain code and also the shape number for a given
% boundary or contour B. B must be a P-by-2 matrix, where P is the number
% of 8-connected boundary pixels for the corresponding region. Each row
% of B represents the row and column coordinates for a pixel. CC is a
% structure with four fields:
%
% StartIdx Row and column coordinates for the starting pixel of
% the boundary B.
%
% ChainCode The 8-connected chain code of B. If B is a P-by-2
% matrix of pixels representing a closed contour, then
% size of this array is 1-by-(P-1). If B is an open
% contour, then size of the chain code is 1-by-P.
%
% FirstDiff The first difference of the chain code, representing
% its rotation-invariant equivalent form and having the
% same dimensions as the chain code.
%
% ShapeNum The shape number of the boundary, which is the first
% difference of the smallest magnitude.