I remembered the function shape_features() which gives a lot of information about shapes in the pic, but either it isn't suitable for yourproblem or I am not able to use it correctly, anyway it will see all 10 blobs as a single shape.
Nevertheless with the help of the very helpful Image Processing E-book that comes with Mathcad I think I found a way to get filled blobs very easy and without trickery. Guess counting will be easier with those shapes.
