For my tasks this function works better than the others I've tried so far. Thank you very much Ohad!!
@Aritra: To run this function on a binary image you have to run:
[X Y] = ind2sub(size(img),find(img));
E = fit_ellipse(x,y);
then you can do:
if E.long_axis > 0
[X, Y] = calcEllipse(E, 360);
end
To plot it the ellipse:
plot(Y, X);
The function calcEllipse:
function [X,Y] = calcEllipse(varargin)
% function [X,Y] = calculateEllipse(x, y, a, b, angle, steps)
%# This functions returns points to draw an ellipse
%#
%# @param x X coordinate
%# @param y Y coordinate
%# @param a Semimajor axis
%# @param b Semiminor axis
%# @param angle Angle of the ellipse (in rad)
%#
% Source: http://stackoverflow.com/questions/2153768/draw-ellipse-and-ellipsoid-in-matlab/24531259#24531259
% Modified by Christian FĂ¤ssler
steps = 360;
if nargin == 1 || nargin == 2
x = varargin{1}.X0_in;
y = varargin{1}.Y0_in;
a = varargin{1}.a;
b = varargin{1}.b;
angle = varargin{1}.phi;
if nargin == 2
steps = varargin{2};
end
else if nargin == 5 || nargin == 6
x = varargin{1};
y = varargin{2};
a = varargin{3};
b = varargin{4};
angle = varargin{5};
if nargin == 6
steps = varargin{6};
end
else
error('Wrong input');
end
end
beta = -angle;
sinbeta = sin(beta);
cosbeta = cos(beta);
alpha = linspace(0, 2*pi, steps)';
sinalpha = sin(alpha);
cosalpha = cos(alpha);
X = round(x + (a * cosalpha * cosbeta - b * sinalpha * sinbeta));
Y = round(y + (a * cosalpha * sinbeta + b * sinalpha * cosbeta));
if nargout==1, X = [X Y]; end
end

5

07 Jul 2014

fit_ellipse
Find the best fit for an ellipse using a given set of points (a closed contour).

Can anyone provide a clear idea about how to implement this practically?
For example if I want to find ellipses in an binary image say bw, how to run this code on the image to get the ellipses?
As I see there is no way to provide the matrix name as a input argument.
And if somebody could explain the input arguments "Input: x,y - a set of points in 2 column vectors. AT LEAST 5 points are needed !"
I mean this statement a bit elaborately it will be very helpful.

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13 Dec 2013

fit_ellipse
Find the best fit for an ellipse using a given set of points (a closed contour).

Great code, very useful!
However, I found a bug related to the orientation of the ellipse and I read some people had the same problem. The author wrote which "to correct that, the test for the orientation_tolerance should be normalized".
How can I solve the problem? May anyone help me? I would be very grateful.
Thanks in advantage, and sorry for my English

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