Patent GB-1015663-A (GB)
Title: Character recognition apparatus and a method of performing character recognition
IPC: G06V30/144
Filed: 1961-12-28
Abstract: 1,015,663. Automatic character reading. GENERAL ELECTRIC CO. Dec. 28, 1961 [Jan. 12, 1961], No. 46457/61. Heading G4R. In character reading apparatus the character is scanned, e.g. by a tracer as described in Specification 1,015,664, by following the outline as shown in Figs. 1 and 2 to derive signals representing the velocities of the tracing spot in the vertical and horizontal directions and means are provided responsive to the rate of change of direction (i.e. the curvature) of the trace line and to the direction of the change (left or right) to obtain a sequence of binary bits from which the character can be identified. The signals X and Y representing the horizontal and vertical components of the tracing spot speed are differentiated at 45, Fig. 3, and 46 to produce the corresponding accelerations #X and #Y. These signals are briefly stored at 47 and 49 and applied with the signals Y and X to multiplying circuits 48, 50. The outputs are subtracted at 51 to produce a signal representing the rate of change of direction of the tracing spot which after passing through a L-P filter (removing noise) is applied to a threshold unit 53, an integrator 54 and a pair of threshold devices 66. The threshold device 53, which consists of biased diodes, responds to a sharp turn in either direction, e.g. the end of a character line or a junction between two lines. Sharp turns are called " corners." The integrator 54, consists of a condenser with feedback amplifier and a diode clamp 65 by which it is reset by each corner signal. The integrator adds up the amount of change in direction in a character segment and a slow curve of predetermined angle produces an output 62 or 62a from one of two diode threshold devices 61 depending upon whether the curve is to the left or right. The threshold devices 66, like device 53, respond to sharp turns, i.e. corners, an output 52 indicating a left-turning corner and output 52a a right-turning corner. The amplitude of the direction change signal remains at the output of the threshold amplifier 55a and is applied to a further threshold device 103 for detecting a sharp acute corner. This is used to distinguish the letter " V " from letter " L." The " V " signal is entered in shift register 69. A shift pulse generator 70 produces pulses for every turn (curve or corner, left or right) to step the registers 60, 69. Into register 60 the corners are entered as " 1 "s, the curves being represented as " 0 "s. Into register 69 all right turns (curves or corners) are entered via Or gate 67 and " 1 "s and left turns are represented by " 0 "s. The outputs of all the register stages are combined in the translator 73 to identify the characters and at the end of the scan when the spot returns to its initial position 34 the identification signal is gated out by gate 72. End of character signal.-To determine the instant when the scan trace has returned to its initial position the #X, #X, #Y and #Y signals are integrated from the beginning of the scan. When all return to zero, as detected by suitable gating and threshold circuits, an end of character pulse C is produced. This pulse delayed resets the registers 60 and 69. A long X signal then moves the spot to the next character. Scan level control.-The vertical position of the scanning spot between characters is maintained correctly by measuring the highest and lowest excursions + Y and - Y and using these signals to set the Y = 0 line.