Abstract

We report on a new method for increasing the linear dynamic range of coherent-optical spatial filters, with special reference to holographic image-deblurring filters. In the filter-generating step, a transmission grating is placed in contact with the transparency representing the spread function of the blur. The spectrum of the spread function then appears in a series of equally spaced islands of different intensities, each occupying a different region of the nonlinear characteristic of the recording medium. Each spatial frequency can then be properly exposed somewhere on the filter, even with a film of limited dynamic range. In the image -processing step, the grating is superposed on the blurred image, the spectrum of which then falls on all the islands of the filter. In this way, the filtering operation is done in parallel channels, each with a different nonlinear characteristic. The channels are combined in the output plane by superposing a grating on the filtered aerial image and viewing this plane through an optical system that does not resolve the grating. Theory, computer simulations, and experimental results are presented. The results show in particular that a good transfer function can be achieved with a hologram-only filter.

© 1973 Optical Society of America

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