how can measure diameter for circle image

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i have an image that have circle shape and i want to measure diameter or distance between two point pleas help me in this regard. I take threshold and i use imtool() but it give pixals i want to measure in mm or cm . thank you all for support

Answers (2)

Image Analyst
Image Analyst on 27 Dec 2016
You forgot to include your image.
Basically segment your image to get just the circle(s) in a binary image. Then use regionprops() to get the equivalent circular diameter.
[labeledImage, numBlobs] = bwlabel(binaryImage);
props = regionprops(labeledImage, 'EquivDiameter');
allDiameters = [props.EquivDiameter];
See my Image Segmentation Tutorial for a full demo http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862
Or you can do it manually with imdistline() like in my attached demo.
  6 Comments
Naja Najah
Naja Najah on 28 Apr 2019
thnx but i'am beginner in matlab and i don't know where in this demo i will multply my distance ?
Image Analyst
Image Analyst on 28 Apr 2019
If you look into the code you'll find a function called DrawLine(). In there, the crucial code is:
instructions = sprintf('Draw a line.\nFirst, left-click to anchor first endpoint of line.\nRight-click or double-left-click to anchor second endpoint of line.\n\nAfter that I will ask for the real-world distance of the line.');
title(instructions);
msgboxw(instructions);
subplot(1,2, 1); % Switch to image axes.
[cx,cy, rgbValues, xi,yi] = improfile(1000);
% Get the profile again but spaced at the number of pixels instead of 1000 samples.
hImage = findobj(gca,'Type','image');
theImage = get(hImage, 'CData');
lineLength = round(sqrt((xi(1)-xi(2))^2 + (yi(1)-yi(2))^2))
[cx,cy, rgbValues] = improfile(theImage, xi, yi, lineLength);
% rgbValues is 1000x1x3. Call Squeeze to get rid of the singleton dimension and make it 1000x3.
rgbValues = squeeze(rgbValues);
distanceInPixels = sqrt( (xi(2)-xi(1)).^2 + (yi(2)-yi(1)).^2);
distanceInRealUnits = distanceInPixels * calibration.distancePerPixel;
distanceInRealUnits is what you want.

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Balakrishnan Sekar
Balakrishnan Sekar on 12 Mar 2021
Edited: Balakrishnan Sekar on 12 Mar 2021
Sir,
Thank you for the demo file. It is very useful. I wanted to measure diameter of a circle (hole) in the image. I have a doubt regarding the 'Enter real world units (e.g. microns):','Enter distance in those units:'. Sir, i want the final value in mm so that i shall the real world units in mm but i couldn't understand enter distance in those units. Could you explain what is that, Which value should i enter? Should i enter the value of the diameter of the circle? The actual diameter of the Circle (hole) is 10 mm, should i enter that value???
Please do explain and help me.
Thanks in advance.
  2 Comments
Image Analyst
Image Analyst on 12 Mar 2021
Then when it asks you for the distance of the line you drew across the Circle (hole), you enter 10 for the distance and mm for the units.
But it looks like your image might be distorted since it does not look like a circle, but an ellipse. You might have to get a calibration factor for each direction, vertical and horizontal.
Balakrishnan Sekar
Balakrishnan Sekar on 12 Mar 2021
No sir, it is actually a circle. But anyhow thank you so much sir. You gave a clear solution.

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