Patent GB-1077565-A (GB)
Title: Apparatus for indicating the segments of a curve
IPC: G06V30/10
Filed: 1965-12-08
Abstract: 1,077,565. Pattern recognition. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 8, 1965 [Dec. 17, 1964], No. 51988/65. Heading G4R. Apparatus for indicating segments of a curve comprises means for measuring the slope of the curve at successive sampling points, means for measuring any change in slope and the direction of said change between successive sampling points, and means for indicating the end of a segment when said change in slope is of a selected magnitude and said direction is a selected direction. A curve follower as in Specification 996,509 (which is referred to) traces round the outline of a character producing horizontal and vertical deflection voltages from which a slope detector as in Specification 1,008,059 (which is referred to) determines the slope producing a 1-out-of-8 marking. This marking (40A) is encoded (41) into both its pure binary equivalent (41A) and its reflected binary equivalent (41B). Each reflected binary slope measurement (except the first) is compared with the preceding such measurement in exclusive-or gates (109 to 112), the number of bit positions in which they differ indicating the change in slope and being counted (113). If the count is four (indicating a slope change of 180 degrees), an end-ofsegment signal (80A) will be produced unconditionally (115, 116). In any event, the count (pure binary) is added (108) to the pure binary version of the first of the two slope measurements, the result being compared (117) with the pure binary second measurement. Provided the count was non-zero, equality and inequality indicate clockwise and anticlockwise direction of change respectively, the comparator (117) setting a direction flip-flop (121) to a corresponding state provided an intervening gate (135) is enabled by the count being non-zero. (The direction flip-flop was set to clockwise at the beginning of tracing since tracing starts in a clockwise sense). When the direction flip-flop (121) is switched, an end-of-segment pulse (80A) will be produced (123, 116) if the count is two or three (124). An end-of-segment pulse (80A) is also produced (128, 116) when a counterclockwise direction of change in one sampling period is followed by the same in the next period, the count being one, two or three in the latter, with the aid of a flip-flop (126) switched whenever the direction flip-flop (121) is switched and enabling an AND gate (128) which is disabled (125, 134) whenever the direction flip-flop (121) is switched. The system is described as providing information for use in designing a character recognition system, a magnetic recorder (70) recording the (already-known) character identity, the slope values, the positions of the segment ends (80A), and data from a " matrix resolver " (30) and from a feature recognition arrangement (60) which is not described but is fed from the slope detector (40) and " matrix resolver " (30). The " matrix resolver " (30) is as in Specification 1,013,036 which is referred to and stores voltages obtained on a preliminary trace around the character to represent its size, effectively divides the character into a 4 x 5 matrix and indicates during subsequent tracing which matrix position the beam is at thus effectively normalizing the character size. The p.r.f. of the sampling pulses may be controlled in accordance with the length of a preliminary trace around the character, thus effectively normalizing its size in another fashion, as described in Specification 1,077,564 which is referred to. The circuitry above producing the end-of-segment pulses may be incorporated in a character recognition system as a feature recognition device.