steer_max.m

加州大学伯克利分校的一个车俩识别程序, 用matlab实现

function [theta,strength,phase,energy] = steer_max(basis)

% [theta,strength,phase,energy] = steer_max(basis)
% returns the local angles of maximum response,
% the strength of the dominant orientation, .
%
% as per freeman & adelson, pami, sept 1991
%
% charless fowlkes, 2000
%

% compute the second and third coeffecients
% of the fourier expansion of the energy 
% function:
%
%   E = C1 + C2*cos(2theta) + C3*sin(2theta) +
%

  C2 = 0.5*(basis.Ga.^2-basis.Gc.^2) + ...
        0.46785*(basis.Ha.^2 - basis.Hd.^2) + ...   
         0.28125*(basis.Hb.^2-basis.Hc.^2) + ...
          0.1875*(basis.Ha.*basis.Hc - basis.Hb.*basis.Hd);
  
  C3 = -(basis.Ga .* basis.Gb) -(basis.Gb .* basis.Gc) ...
         -0.9375*(basis.Hc .* basis.Hd + basis.Ha .* basis.Hb) ...
          -1.6875 * basis.Hb .* basis.Hc - 0.1875 * basis.Ha .* basis.Hd;

% use the low order coeficients to estimate
% the orientation of greates energy at each
% point as well as the strength at that point

  theta = 0.5*atan2(C3,C2); 
  strength = sqrt(C2.^2 + C3.^2);

  if(nargout>2)
    % compute theta for a smoothed version
    % of the image.  steer the filter in the
    % most energetic direction at each of 
    % those points and compute the phase 
    % response in that direction ...
    
    Za = smooth_image(strength.*C2,1);
    Zb = smooth_image(strength.*C3,1);
    Q = 0.5*atan2(Zb,Za);
    
    [G2,H2] = steer(Q,basis);
    
    phase = abs(atan2(H2,G2));
    energy = G2.*G2 + H2.*H2;
  end