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A feature-extraction and vector-generation VLSI has been developed for real-time image recognition. An arrayed-shift-register architecture has been employed in conjunction with a pipelined directional-edge-filtering circuitry. As a result, it has become possible to scan an image, pixel by pixel, with a 64 x 64-pixel recognition window and generate a 64-dimensional feature vector in every 64 clock cycles. In order to determine the threshold for edge-filtering operation adaptive to local luminance variation, a high-speed median circuit has been developed. A binary median search algorithm has been implemented using high-precision majority voting circuits working in the mixed-signal principle. A prototype chip was designed and fabricated in a 0.18-mum 5-metal CMOS technology. A high-speed feature vector generation in less than 9.7 ns/vector element has been experimentally demonstrated. It is possible to scan a VGA-size image at a rate of 6.1 frames/s, thus generating as many as 1.5 x 106 feature vectors per second for recognition. This is more than 103 times faster than software processing running on a 3-GHz general-purpose processor.
Date of Publication: Sept. 2007