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a guest Apr 6th, 2016 126 Never
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  1.  
  2.  
  3. % img = noise(50+100*gaussf(rr>85,2),'gaussian',20)
  4. img = zeros(250);
  5. img(:,1:end/2) = 1;
  6. img = noise(50+100*gaussf(img,2),'gaussian',20)
  7.  
  8. s = zeros(60,2);
  9. s(:,2) = 1;
  10. s(1,2) = 50;
  11. s = cumsum(s);
  12. s(:,1) = 160;
  13.  
  14. x = s(:,1);
  15. y = s(:,2);
  16. % x = 120+50*cos(0:0.1:2*pi)';
  17. % y = 140+60*sin(0:0.1:2*pi)';
  18. hold on, plot([x;x(1)],[y;y(1)],'g')
  19.  
  20. alpha = 0.001;
  21. beta = 0.4;
  22. gamma = 100;
  23. iterations = 50;
  24.  
  25. N = length(x);
  26. a = gamma*(2*alpha+6*beta)+1;
  27. b = gamma*(-alpha-4*beta);
  28. c = gamma*beta;
  29.  
  30. P = diag(repmat(a,1,N));
  31. P = P + diag(repmat(b,1,N-1), 1) + diag(   b, -N+1);
  32. P = P + diag(repmat(b,1,N-1),-1) + diag(   b,  N-1);
  33. P = P + diag(repmat(c,1,N-2), 2) + diag([c,c],-N+2);
  34. P = P + diag(repmat(c,1,N-2),-2) + diag([c,c], N-2);
  35. %
  36.  
  37. d = gamma * (-alpha);
  38. e = gamma * (2*alpha);
  39.  
  40. P(1:2,:) = 0;
  41. P(1,1) = -gamma;
  42. P(2,1) = d;
  43. P(2,2) = e;
  44. P(2,3) = d;
  45.  
  46. P(N-1:N,:) = 0;
  47. P(N-1,N-2) = d;
  48. P(N-1,N-1) = e;
  49. P(N-1,N) = d;
  50. P(N,N) = -gamma;
  51.  
  52. P = inv(P);
  53. f = gradient(gradmag(img,30));
  54.  
  55. for ii = 1:iterations
  56.    % Calculate external force
  57.    coords = [x,y];
  58.    fex = get_subpixel(f{1},coords,'linear');
  59.    fey = get_subpixel(f{2},coords,'linear');
  60.    % Move control points
  61.    x = P*(x+gamma*fex);
  62.    y = P*(y+gamma*fey);
  63. %    if mod(ii,5)==0
  64.       plot([x;x(1)],[y;y(1)],'b')
  65. %    end
  66. end
  67. plot([x;x(1)],[y;y(1)],'r')
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