center of mass of binary image

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Yeshudas Muttu
Yeshudas Muttu on 20 Sep 2014
Answered: gwoo on 21 Mar 2019
hi , i want to know how to calculate center of mass of the binary image(silhouette).below is the image where i have crop the image basedon it boundary box

Accepted Answer

Image Analyst
Image Analyst on 20 Sep 2014
Image Analyst
Image Analyst on 24 Sep 2014
Yep, my code will do that. Did you see how if found each coin and cropped it out. I was hoping you could adapt it yourself after seeing how I used regionprops to ask for hte bounding box and then used this code to crop out all the blobs:
message = sprintf('Would you like to crop out each coin to individual images?');
reply = questdlg(message, 'Extract Individual Images?', 'Yes', 'No', 'Yes');
% Note: reply will = '' for Upper right X, 'Yes' for Yes, and 'No' for No.
if strcmpi(reply, 'Yes')
% Maximize the figure window.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
for k = 1 : numberOfBlobs % Loop through all blobs.
% Find the bounding box of each blob.
thisBlobsBoundingBox = blobMeasurements(k).BoundingBox; % Get list of pixels in current blob.
% Extract out this coin into it's own image.
subImage = imcrop(originalImage, thisBlobsBoundingBox);
% Determine if it's a dime (small) or a nickel (large coin).
if blobMeasurements(k).Area > 2200
coinType = 'nickel';
coinType = 'dime';
% Display the image with informative caption.
subplot(3, 4, k);
caption = sprintf('Coin #%d is a %s.\nDiameter = %.1f pixels\nArea = %d pixels', ...
k, coinType, blobECD(k), blobMeasurements(k).Area);
title(caption, 'FontSize', 14);
Did you actually download and run my demo? Do you think you'll be able to transfer that code to your program?

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More Answers (2)

gwoo on 21 Mar 2019
This is the fastest simpliest way I've seen to do it without regionprops:
[r, c] = find(binaryImage == 1);
rowcolCoordinates = [mean(r), mean(c)];

Guillaume on 20 Sep 2014
Edited: Guillaume on 20 Sep 2014
You haven't attached any image.
If your image is a single connected blob, regionprops can give you the centre of mass with the centroid property.
If you want the centre of mass for the whole image, regardless of how many blobs are in it, it's fairly trivial:
[x, y] = meshgrid(1:size(img, 2), 1:size(img, 1));
weightedx = x .* img;
weightedy = y .* img;
xcentre = sum(weightedx(:)) / sum(img(:));
ycentre = sum(weightedy(:)) / sum(img(:));


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