activecontour.m

这是一个利用水平集方法进行分割的方法

function phi = activecontour( u0, center, radius, isinside, d_it, m_it, m_name )
% ACTIVECONTOUR Segment an image using active contours
%    ACTIVECONTOUR( u0, center, radius, isinside, d_it, m_it, m_name )
%    segments the image u0 with initial segmented region as a
%    circle with argument center and radius. The current segmented
%    image is displayed every d_it iterations and written to disk
%    every m_iterations with name m_name*.png.

% constants
ITERATIONS = 1000;
delta_t = 0.1;
lambda1 = 1;
lambda2 = 1;
nu = 0;
h = 1; h_sq = h^2;
epsilon = 1;
mu = 0.01 * 255^2;

% initialize phi to signed distance function from circle
phi = initphi( size( u0 ), center, radius, isinside );

for ii = 1 : ITERATIONS;

  % display current iteration
  fprintf( 1, '%d\n', ii );

  % display the segmented image every 'd_it' iterations
  if( mod( ii - 1, d_it ) == 0 )
    disp( 'Displaying Segmented Image' );
    segim = createimage( u0, phi );
    clf; imshow( segim );
    drawnow;
  end;

  % write current segmented image to file every 'm_it'
  % iterations
  if( mod( ii - 1, m_it ) == 0 )
    segim = createimage( u0, phi );
    filename = strcat( m_name, sprintf( '%06d', ( ( ii - 1 )/ m_it ) + 1 ), '.png' );
    imwrite( segim, filename );
  end;

  % compute dirac(phi) * delta_t factor
  dirac_delta_t = delta_t * dirac( phi, epsilon );

  % calculate inside and outside curve terms
  [ inside, outside ] = calcenergy( u0, phi, epsilon );
  energy_term = -nu - lambda1 .* inside + lambda2 .* outside;

  % calculate central differences
  dx_central = ( circshift( phi, [ 0, -1 ] ) - circshift( phi, [ 0, 1 ] ) ) / 2;
  dy_central = ( circshift( phi, [ -1, 0 ] ) - circshift( phi, [ 1, 0 ] ) ) / 2;

  % calculate the divergence of grad_phi/|grad_phi|
  abs_grad_phi = ( sqrt( dx_central.^2 + dy_central.^2 ) + 0.00001 );
  x = dx_central ./ abs_grad_phi;
  y = dy_central ./ abs_grad_phi;
  grad_term = ( mu / h_sq ) .* divergence( x, y );

  % calculate phi^n+1
  phi = phi + dirac_delta_t .* ( grad_term + energy_term );

end;