If you have the binarized image, just use regionprops.
inpict = imread('blobs.png');
S = regionprops(inpict,'centroid')
Note that I'm not using your image in this example. I don't want to deal with cropping all the padding off, and the size (and thus the coordinates) are probably altered now anyway. Don't save images by saving the displayed figure. There's rarely a good reason to degrade images by doing that. Just use imwrite().