How can I calculate all the distances between the centroid and every white pixel in the shape of ellipse?

In my image called shape I have an ellipse with a white shape(all image is black, only the shape is white), I try to calculate the distances between the centroid and every white pixel in the shape, after that, will calculat the histogram by this distances. I tried with this code (of course after geting the centroid): shape.Centroid(x,y); [a,b]=find(shape==1); (know I need a for) for a=?:? for b=?:? distance=sqrt((x-ai)^2+(y-bi)^2); end end