How to fit an ellipse to an image in matlab.

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Hardit Singh 2019-12-9

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https://ww2.mathworks.cn/matlabcentral/answers/495720-how-to-fit-an-ellipse-to-an-image-in-matlab

评论： Connor 2023-11-11

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.

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采纳的回答

Akira Agata 2019-12-11

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https://ww2.mathworks.cn/matlabcentral/answers/495720-how-to-fit-an-ellipse-to-an-image-in-matlab#answer_405863

How about the following?

% Read image
I = imread('diskimage1.jpeg');
% 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);
M = makehgtform('translate',[s.Centroid, 0],'zrotate',deg2rad(-1*s.Orientation));
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)

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Image Analyst 2023-11-10

@Connor that is not a blob. Well it is but it's a very snake-like, line-like blob. So the fit is accurate. But I suspect what you want is to fit the (x,y) coordinates of the blob to an ellipse. So you need to get x and y from the binary image like this:

[y, x] = find(binaryImage);

and then use the ellipse fit in the FAQ: https://matlab.fandom.com/wiki/FAQ#How_can_I_fit_an_ellipse_or_other_shape_to_a_set_of_XY_data?

Connor 2023-11-11