An active pixel sensor (APS) with two-dimensional winner-take-all (WTA) detection is presented. This system-on-a-chip employs adaptive spatial filtering of the processed image, with bad pixel elimination and false alarm reduction in case of a missing object. The circuit has a unique ability of adaptive spatial filtering that allows removal of the background from the image, one stage before it is transferred to the WTA detection circuit. A test chip of a 64 64 array has been implemented in 0.5-m

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... CMOS technology, has a 49% fill factor, is operated by a 3.3-V supply, and dissipates 36 mW at video rate. System architecture and operation are discussed and measurements from the prototype chip are presented. Index Terms-Active pixel sensor (APS), CMOS, filter, image processing, pattern recognition, spatial filtering, very large scale integration (VLSI), winner-take-all (WTA).