Patent GB-1234941-A (GB)
Title: Improvements in or relating to pattern recognition devices
Inventor: LEMAY CHRISTOPHER ARCHIBALD GO
IPC: G06V30/146
Filed: 1967-08-16
Abstract: 1,234,941. Pattern recognition. EMI Ltd. 5 Aug., 1968 [16 Aug., 1967], No. 37657/67. Heading G4R. In a pattern recognition device, scanning waveforms supplied to a scanner scanning an unknown pattern are repetitively modified to reduce registration error between a representation of the pattern from the scanning and a representation of one of a plurality of stored known patterns selected by comparison of representations, until the degree of correspondence between the unknown pattern representation and the last selected known pattern representation exceeds a threshold. As described, X and Y triangular scanning waveforms of slightly different frequency are fed to a flying-spot scanner to scan an unknown pattern in a series of orthogonal diagonals, to an area selector which uses thresholders and logic to indicate the quadrant the scan is in, and to scanner(s) in a pattern store to scan standard optical patterns. In general, the unknown pattern is scanned completely a plurality of times, the binarized pattern signals from the scanner being correlated, in each scanning, with similar signals from each of the standard patterns, the standard pattern signals giving the best correlation in a given scanning being fed to an error calculator together with the binarized unknown-pattern signal during the next scanning. The error calculator produces error signals which are combined with each other and the output of the area selector to update a modification store which controls modification of the scanning waveforms as they are applied to the scanner scanning the unknown pattern. The updating occurs at the end of each scanning of the pattern, but is prevented whenever the standard pattern giving the best correlation in this scanning is different from that in the last scanning. Operation continues in this way until the best correlation exceeds a threshold and differs from the next best by at least a threshold amount. Details of error features above.-The unknown-pattern signals, and the signals from the standard pattern which gave the best correlation with the unknown pattern during the last scanning of the unknown pattern, are applied to 70, 71, respectively (see Fig. 6 (a), top left) to adder 47 and subtractor 73 as shown. The output of adder 47 feeds differentiator 72 and the outputs of 72,73 are multiplied at 74, the product being gated at 75, 76, 80-84 under control of the X and Y scanning waveforms t, t<SP>1</SP> according as the slopes of these are positive or negative to allow for the direction of the current scan line, unit 82 being a phase inverter. The resulting two signals are added and subtracted (with integration) at 90, 91 to produce horizontal and vertical error signals respectively, which are gated according to the quadrant under control of the area selector at 92- 99, to feed a matrix (not shown) which adds and subtracts them in various combinations to produce trains of positive and negative pulses representing the extents of respective pattern displacements, size errors and distortions. Each train is accumulated separately to supply, at the end of a scanning of the pattern, a three-state signal. The three-state signals are used to increment/decrement corresponding quantities in the modification store, these quantities, with or without multiplication by respective "factors", being added to the scanning waveforms applied to scan the unknown pattern. The "factors" used are the present amplitudes of the unmodified scanning waveforms, and the product of these. A modification replaces units 47, 72-74 by units which form the product of the two inputs with the standard pattern delayed and the product with it not delayed, and difference the two products.