how to calculate the major and minor axis of an ellipse in contour plot

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dEEPAK MAT
dEEPAK MAT 2013-11-14
评论： Image Analyst 2021-1-12
I have a contour plot which is more of a ellipse.I would like to know its major and minor axis...a and b respectively.How do i go about.I am naive user please guide me.

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Image Analyst
Image Analyst 2013-11-14
You need the Image Processing Toolbox. Type ver to see if you have it.
It looks like an indexed image with a jet colormap being applied. Get one "ring" by thresholding
binaryImage = grayImage == theValue; % Different rings will have different intensity values.
% Now get the ellipse parameters with regionprops.
measurements = regionprops(binaryImage, 'MajorAxisLength', 'MinorAxisLength', 'Orientation');
majorAxisLength = measurements.MajorAxisLength;
minorAxisLength = measurements.MinorAxisLength;
% Repeat for other rings.

更多回答（2 个）

Mohammad Bhat
Mohammad Bhat 2018-2-11
How can I pass ellipse as an object to regionprops
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Rahul Verma
Rahul Verma 2020-1-6
I am having a similar contour image which I converted to grayscale as attached...
a=imread('test1.png');
grayImage = rgb2gray(a);
grayscale.pngbinaryImage = grayImage == 0.40;
measurements = regionprops(binaryImage, 'MajorAxisLength', 'MinorAxisLength', 'Orientation');
However, on calling regionprops, I get an empty matrix
0×1 empty struct array with fields:
MajorAxisLength
MinorAxisLength
Orientation
As a result, I cannot get the major and minor axis lengths...
Any suggestions :)test1.png
Image Analyst
Image Analyst 2020-1-6
You probably don't have anything that is EXACTLY 0.4. Try
binaryImage = grayImage >= 0.40;
Do it again for a different value and AND the images if you just want the ring.
binaryImage = grayImage >= 0.40 & grayImage <= someOtherValue;

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Bhavesh Garg
Bhavesh Garg 2021-1-12
VHVHV

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