# How to fit an ellipse to an image in matlab.

165 views (last 30 days)
Hardit Singh on 9 Dec 2019
Commented: Image Analyst on 29 Jun 2020
I have a image like this and I want to fit an ellipse around this disk image and get the info about the ellipse like its axis, center point, etc. I am unsure how to use the image proccessing toolbox to draw an ellipse to it and get info about the ellipse.

Akira Agata on 11 Dec 2019
% Binarize
Igray = rgb2gray(I);
BW = imbinarize(Igray);
% Extract the maximum area
BW = imclearborder(BW);
BW = bwareafilt(BW,1);
% Calculate centroid, orientation and major/minor axis length of the ellipse
s = regionprops(BW,{'Centroid','Orientation','MajorAxisLength','MinorAxisLength'});
% Calculate the ellipse line
theta = linspace(0,2*pi);
col = (s.MajorAxisLength/2)*cos(theta);
row = (s.MinorAxisLength/2)*sin(theta);
D = M*[col;row;zeros(1,numel(row));ones(1,numel(row))];
% Visualize the result
figure
imshow(Igray)
hold on
plot(D(1,:),D(2,:),'r','LineWidth',2)
Image Analyst on 29 Jun 2020
You can get the boundary of your binary image with bwboundaries. Then use sqrt() to find the distance of every actual boundary point to the closest fit point. Find the closest one with min. Then take the mean or sum of those closest distances.
boundaries = boundaries{1}; % Extract from cell
xb = boundaries(:, 2);
yb = boundaries(:, 1);
closestDistances = zeros(1, length(xb));
for k = 1 : length(xb)
% Get distance of each actual boundary point to all points in your ellipse fit vectors.
distances = sqrt((xFit - xb(k)) .^ 2 + (yFit - yb(k)) .^ 2); % A vector of distances
closestDistances(k) = min(distances); % A single distance.
end
closenessOfFitMetric = mean(closestDistances)

Image Analyst on 11 Dec 2019

R2016b

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!