Analog-to-digital (A-D) conversion of intensity transmittance (or reflectance) can be accomplished through nonlinear coherent optical image processing. Theoretically speaking, for any given positive integer N, 2^N discrete levels of transmittance (or reflectance) can be digitized into binary form simultaneously via pure optical means, involving the proper design and fabrication of a specific halftone screen. The digital outputs of the N bit-planes are selected at the Fourier plane by spatial filtering the (2ⁿ − 1)th diffraction order, where n = 1, 2, …, and N, respectively. The specific halftone screen must have (2^N - 1) gray levels, and it should be emphasized that only a single halftone photograph is required for the optical A-D conversion. The general principle of this new method and a preliminary experimental result of an eight-level A-D conversion are described in this paper.

© 1978 Optical Society of America.

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