MATLAB Answers


Center of mass in binary image

Asked by Felix
on 18 Sep 2013
Latest activity Commented on by Walter Roberson
on 16 Dec 2016

Hello, I have a binary image with one object. How can I calculate the center of this object, to mark it in my image and to write the coordinates in the corner of this image, like this: object: X, Y

I used this code to calculate the center of mass:

s = regionprops(bw, 'centroid');

centroids = cat(1, s.Centroid);


hold on

plot(centroids(:,1), centroids(:,2), 'b*')

hold off

but how can i plot this coordinates on my image in the left corner?

Thank you for help


Log in to comment.


No tags are associated with this question.

3 Answers

Answer by David Sanchez
on 18 Sep 2013
 Accepted Answer

use text command:

your_string = strcat( num2str(centroids(:,1)),'-', num2str(centroids(:,2)));

change the position by changing the "10,10" values


Thank you it's works, another question, how can i write in this way:

Object: X,Y(coordinates)

now it gives me only a coordinates and can i also write a coordinates without a numbers after '.'? only integers

Use sprintf to create your string, and cast your numbers to integers or use %.0f:

textString = sprintf('Object: %d, %d (coordinates)', int32(X), int32(Y));

Log in to comment.

Answer by Walter Roberson
on 18 Sep 2013

ndgrid() of 1:width and 1:height, do a logical indexing of those according to the binary image, calculate the mean() of what is left in each of the two coordinate matrices. Result will be centre of mass along each of the two coordinates.


Log in to comment.

Answer by Mauldy Putra on 16 Dec 2016

i want to ask, in your code there is bw i want to know what is bw stand for? cause i try use your code it's said "Undefined function or variable 'bw'."

thank you

  1 Comment

bw is the binary image whose center of mass is to be found.

Log in to comment.

Discover what MATLAB® can do for your career.

Opportunities for recent engineering grads.

Apply Today