An optical analog computing system which can discriminate shapes and/or sizes of small objects by a Multiplexed Matched Spatial Filter (MMSF) has been developed. The system discriminates the shapes and/or sizes of particles instantaneously and simultaneously. The optical analog computing system is composed of three parts; (1) catching particle images, (2) discriminating the shapes and/or sizes and (3) displaying auto-correlation signals as the spatial distributions of particles. The MMSF of holographic filter is made by a new process in which holograms are made automatically and instantaneously with a photo-conductor plastic plate processed by solvent vapor. Spatial distributions of particles are visualized according to the shape and/or size by the optical analog computing system.