Coherent-optical Fourier transformation of video images can be very powerful; a set-up will be described. The modulation of the coherent beam occurs in a spatial light modulator where the liquid crystal display image of the object is projected onto an optically addressed spatial light modulator that uses bismuth silicium oxide for photoconduction and a twisted nematic liquid crystal as a birefringent layer. Edge enhancing of the image can occur; in addition, it appears that the Fourier spectrum

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... of an edge is asymmetric due to local phase variations. The set-up was applied to recognize objects at different positions. A chargecoupled device matrix camera detects the Fourier plane, in the personal computer the pixels are summed up to ring-wedge-segments and processed for pattern recognition.