What formula MATLAB uses to find centroid of image?

I know, we can get centroid by writing following:

 stat = regionprops(BW, 'Centroid') ;

 c = stat.Centroid

But how can I find centroid of image using mathematical expressions?

I want to know what expression MATLAB uses to find centroid.

Answer 1

[Walter Roberson]

http://en.wikipedia.org/wiki/Image_moment