Are you working with binary images. If so, then the following code will help you find the centroid of the image:

% read the image

i = imread('ball.bmp');

% convert to double

i = double(i);

% invert the image so that we can label the image

% the invert function is not given in the DIP toolbox

% i am attaching it with this email

i = invert(i);

% apply 8-connected algo

[labels,count] = bwlabel(i,8);

% calculate features. For more type help imfeature

features = imfeature(labels,'Centroid');

i = 1;

while i <= count

        % display centroid of all the subimages in the image

       disp(features.Centroid);

       i = i + 1;

end

 

Hope this helps.

Good luck