Active geometric shape models
26 Sep 2012
28 Sep 2012)
The active geometric shape model is a novel approach for fitting a geometric shape in images.
|GVF(f, alpha, mu, ITER)
function [u,v] = GVF(f, alpha, mu, ITER)
% GVF Compute gradient vector flow.
% [u,v] = GVF(f, mu, ITER) computes the
% GVF of an edge map f. mu is the GVF regularization coefficient
% and ITER is the number of iterations that will be computed.
% Chenyang Xu and Jerry L. Prince 6/17/97
% Copyright (c) 1996-99 by Chenyang Xu and Jerry L. Prince
% Image Analysis and Communications Lab, Johns Hopkins University
% modified on 9/9/99 by Chenyang Xu
% MATLAB do not deal their boundary condition for gradient and del2
% consistently between MATLAB 4.2 and MATLAB 5. Hence I modify
% the function to take care of this issue by the code itself.
% Also, in the previous version, the input "f" is assumed to have been
% normalized to the range [0,1] before the function is called.
% In this version, "f" is normalized inside the function to avoid
% potential error of inputing an unnormalized "f".
[m,n] = size(f);
fmin = min(f(:));
fmax = max(f(:));
f = (f-fmin)/(fmax-fmin); % Normalize f to the range [0,1]
f = BoundMirrorExpand(f); % Take care of boundary condition
[fx,fy] = gradient(f); % Calculate the gradient of the edge map
u = fx; v = fy; % Initialize GVF to the gradient
SqrMagf = fx.*fx + fy.*fy; % Squared magnitude of the gradient field
% Iteratively solve for the GVF u,v
u = BoundMirrorEnsure(u);
v = BoundMirrorEnsure(v);
u = u + alpha * ( mu*4*del2(u) - SqrMagf.*(u-fx) );
v = v + alpha * ( mu*4*del2(v) - SqrMagf.*(v-fy) );
% fprintf(1, '%4d', i);
% if (rem(i,20) == 0)
% fprintf(1, '\n');
u = BoundMirrorShrink(u);
v = BoundMirrorShrink(v);