Original SEM image of particles.
All particles are spheres and they are very close to each other and overlapped.
Binary image after applying a threshold to the original. Distance map of the binary image. Each maximum on the distance map is corresponded to the center of the particle and the amplitude of the maximum is particle's radius. Creating the intensity calibration corresponded to Distance map, count and measure amplitudes of the maximums. Optical density values give us diameters of the particles.