The United States of America As Represented by the United States

Leland Stanford Junior University

Ellen Ochoa

Donald W Sweeney

Lambertus Hesselink

Jan Philip Allebach

Joseph W Goodman

George F Schils

A hybrid optical/electronic system performs median filtering and related ranked-order operations using threshold decomposition to encode the image. Threshold decomposition transforms the nonlinear neighborhood ranking operation into a linear space-invariant filtering step followed by a point-to-point threshold comparison step. Spatial multiplexing allows parallel processing of all the threshold components as well as recombination by a second linear, space-invariant filtering step. An incoherent optical correlation system performs the linear filtering, using a magneto-optic spatial light modulator as the input device and a computer-generated hologram in the filter plane. Thresholding is done electronically. By adjusting the value of the threshold, the same architecture is used to perform median, minimum, and maximum filtering of images. A totally optical system is also disclosed.

Optical ranked-order filtering using threshold decomposition

A method for recognizing the presence of a particular target in a field of view which is target position, rotation, and intensity invariant includes the preparing of a target-specific invariant filter from a combination of all eigen-modes of a pattern of the particular target. Coherent radiation from the field of view is then imaged into an optical correlator in which the invariant filter is located. The invariant filter is rotated in the frequency plane of the optical correlator in order to produce a constant-amplitude rotational response in a correlation output plane when the particular target is present in the field of view. Any constant response is thus detected in the output

Position, rotation, and intensity invariant recognizing method

An optical system for selectively enhancing and/or suppressing the spectral intensity of components in an object beam, is disclosed. In one exemplary application, the optical system includes means for performing a forward transform operation on an input beam, a non-linear optical medium such as, for example, Bi.sub.12 SiO.sub.20 or Bi.sub.12 GeO.sub.20 and means for performing an inverse transform operation. In operation, the forward transform is performed on an input beam that contains a complex function characteristic of an object or subject, the resulting transform of the object beam is applied to the non-linear optical medium to form a hologram, then the hologram is read-out and the inverse transform operation is performed to provide an output optical beam that contains, for example, selectively enhanced intensity components and/or selectively suppressed intensity components. In one specific application, the object beam is obtained by transmitting a laser beam through a photomask such as, for example, the type used for fabricating semiconductor integrated circuits, the non-linear properties of the photorefractive crystal provide filtering or inversion of the intensity of the periodic aspects of the mask in the hologram and phase conjugate read-out and inverse transformation provide an image in which the intensity of the non-periodic defects is enhanced. In a second application, image inversion is employed to provide real-time inversion of intensity in the output image.

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Pleasanton, CA, United States of America

Ellen Ochoa