# How can I visually isolate and measure a round object within my MATLAB image?

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MathWorks Support Team on 27 Jun 2009
Commented: Image Analyst on 31 Oct 2017
How can I visually isolate and measure a round object within my MATLAB image?
Do you have an example that shows how to do the following in MATLAB:
1. Select a round object in the image
2. Fill the rest of image with a background color
3. Draw an outline around the object
4. Find the diameter and center of the object

MathWorks Support Team on 27 Dec 2016
Here is an example on how to visually isolate and measure a round object within an image in MATLAB:

imshow(I)
BW = roipoly(I);
% manually select region here
BW1 = not(BW);
J = roifill(I,BW1); imshow(J)
% using ipexsegcell demo
% type 'ipexsegcell' from the MATLAB command prompt
% to view documentation for this demo
BWs = edge(J, 'sobel', (graythresh(I) * .1));
se90 = strel('line', 3, 90);
se0 = strel('line', 3, 0);
BWsdil = imdilate(BWs, [se90 se0]);
BWdfill = imfill(BWsdil, 'holes');
figure, imshow(BWdfill);
title('binary image with filled holes');
BWnobord = imclearborder(BWdfill, 4);
figure, imshow(BWnobord), title('cleared border image');
seD = strel('diamond',1);
BWfinal = imerode(BWnobord,seD);
BWfinal = imerode(BWfinal,seD);
figure, imshow(BWfinal), title('segmented image');
BWoutline = bwperim(BWfinal);
Segout = I;
Segout(BWoutline) = 255;
figure, imshow(Segout), title('outlined original image');
% find diameter and center of the selected coin
[i,j] = find(BWfinal);
i1 = unique(i);
j1 = unique(j);
diameter = max(i)-min(i)
center_i = floor(mean(i1))
center_j = floor(mean(j1))
Additionally, another demonstration you can look into is the following MathWorks FileExchange submission:
http://www.mathworks.com/matlabcentral/fileexchange/25157-image-segmentation-tutorial
##### 2 CommentsShowHide 1 older comment
Image Analyst on 31 Oct 2017
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Image Analyst on 20 Nov 2016
I do not recommend the accepted answer. See my Image Processing Tutorial for a much better and simpler method. http://www.mathworks.com/matlabcentral/fileexchange/25157-image-segmentation-tutorial You can simply threshold and call regionprops. There is no need for all that unnecessary edge detection and morphology stuff.

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