MATLAB: Fitting an ellipse to the binary iris image

Question

I want to fit an ellipse to the boundary of the iris in my edge map eye image in order to segment the iris from the background.i really appretiate your help. the image is :

http://imageshack.us/photo/my-images/94/irisseg2.png/

thanks inadvance.

na

Answer 1

function report=ellipsefit(XY)
%ELLIPSEFIT - form 2D ellipse fit to given x,y data
%






%  report=ellipsefit(XY)
%
%in:
%
% XY: Input matrix of 2D coordinates to be fit. Each column XY(:,i) is [xi;yi]
%
%out: Finds the ellipse fitting the input data parametrized both as
%     A*x^2+B*x*y C*y^2+D*x+E*y=1 and [x-x0,y-y0]*Q*[x-x0;y-y0]=1
%
% report: a structure output with the following fields
%    
%    report.Q: the matrix Q
%    report.d: the vector [x0,y0]
%    report.ABCDE: the vector [A,B,C,D,E]
%    report.AxesDiams: The minor and major ellipse diameters
%    report.theta: The counter-clockwise rotation of the ellipse.
%
%NOTE: The code will give errors if the data fit traces out a non-elliptic or
%      degenerate conic section.
%
%See also ellipsoidfit
X=XY(1,:).';
Y=XY(2,:).';
M= [X.^2, X.*Y, Y.^2, X, Y, -ones(size(X,1),1)];
[U,S,V]=svd(M,0);
ABCDEF=V(:,end);
if size(ABCDEF,2)>1
      error 'Data cannot be fit with unique ellipse'
  else
      ABCDEF=num2cell(ABCDEF);
  end
[A,B,C,D,E,F]=deal(ABCDEF{:});
Q=[A, B/2;B/2 C];
x0=-Q\[D;E]/2;
dd=F+x0'*Q*x0;
Q=Q/dd;
[R,eigen]=eig(Q);
eigen=eigen([1,4]);
if ~all(eigen>=0), error 'Fit produced a non-elliptic conic section'; end
idx=eigen>0;
eigen(idx)=1./eigen(idx);
AxesDiams = 2*sqrt(eigen);
theta=atand(tand(-atan2(R(1),R(2))*180/pi));
report.Q=Q;
report.d=x0(:).';
report.ABCDE=[A, B, C, D, E]/F;
report.AxesDiams=sort(AxesDiams(:)).';
report.theta=theta;