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We describe a real-time image-processing scheme that uses selective erasure of spatial frequencies at the Fourier transform plane in an arrangement employing photorefractive two-beam coupling. The versatility of the device results from the use of the Fourier transform of the erasure beam, which counterpropagates to the image-bearing beam. The technique can perform spatial-filtering operations such as edge enhancement, bandpass filtering, and pattern recognition by controlling the information available at the erasure-beam Fourier plane. An experimental demonstration has been made on edge enhancement, bandpass filtering, and character recognition.

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