Hi Ali. I did it by trial and error. It you wanted to approach from a scientific viewpoint you would use regionprops to get the diameter/ dimensions of an object. Then work out a suitable structural element. thanks Anselm
Hello sir! thanks for the answer, actually I was using another image that's why I wanted to know the method and one more thing which came to my mind is that during surfing of the background, why a black surfing is obtained for coloured image?