Focal plane location using integrated gray-level gradient method in digital particle holography

To accurately locate the focal plane of the object in digital particle holography, the integrated gray-level gradient method is presented. This method consists of a conventional edge-sharpness [Es] method and a new method, namely, overall-sharpness [Os] method which is an efficient supplement of the former. The respective scopes of application of above criterions were discussed by using numerical simulation holograms of particles. At last, the integrated gray-level gradient method was applied to the real holograms of dot array target, calibration target and glass bead. The experiment results demonstrate that this method can effectively extract the focal plane of particle.