The study of digital optical information processing by a computer has been performed. As the experimental device, a halftone plotter has been developed which is able to plot the data obtained from an electronic computer with continuous-tone on a conventional cathode ray tube. The capability of producing a halftone drawing by this plotter is useful for displaying optical information processed by a computer. The digital optical information processing studied here is based on this continuous-tone drawing and the reduction of the amount of computer time for the Fourier transform by the new algorithm of the fast Fourier transform. The fast Fourier transform has made it possible to compute in a short time the Fourier spectrum of the object, the convolution integral, the correlation function, etc., by even a middle class computer. These techniques have been applied to some examples. The simulation of filtering and the image restoration by a computer are attempted. The digitized holograms are then synthesized by a computer and are displayed by this plotter on a cathode ray tube as digitized halftone patterns. These holograms are recorded on films and are photoreduced. An image reconstruction is achieved optically for both black-and-white objects and the halftone object. The use of the halftone plotter has permitted us to simplify the theoretical background of the synthesis of a computer-generated hologram. Furthermore, any spatial filters can be made by computer processing.
Yoshiki Ichioka, Masaharu Izumi, and Tatsuro Suzuki, "Halftone Plotter and Its Applications to Digital Optical Information Processing," Appl. Opt. 8, 2461-2471 (1969)