Patent GB-1252583-A (GB)
IPC: G06V30/146
Filed: 1968-10-01
Abstract: 1,252,583. Character recognition. INTERNATIONAL BUSINESS MACHINES CORP. 1 Oct., 1968 [3 Oct., 1967], No. 46425/68. Heading G4R. In a character recognition system, the operation of character-scanning means and recognition means are adjusted in accordance with a control word from a data processing unit. A control word from a computer is gated into registers and flip-flops and specifies the vertical and horizontal addresses (i.e. positions in the scanning field) of a position from which scanning of a line of characters or a calibration mark (see below) is to start, a (horizontal) end-of-line address, whether calibration is required, whether the characters will be numeric or alphabetic or handwritten and the font if applicable (to select the type of scanning and inform the recognition circuits), whether large blank areas between characters are expected (in which case the recognition circuits and the scan control cause high speed scan through blank areas), the orientation of the characters on the document (one " rotation " bit), and whether reject characters are to be corrected on or off line. The deflection voltages of the CRT in the flying-spot scanner used are also fed to a display CRT which displays the character being scanned since this is done by outline-following. If correction is to be done on line, a reject signal from the recognition circuits causes scanning of the character to be repeated until the operator actuates a keyboard to enter the character identity after observing the display CRT. If correction is to be done off line, a reject signal causes the document to be routed to a reject pocket. Positioning of the scanner beam at the beginning of a line of characters or adjacent to a calibration mark, and termination of the scan on reaching line-end, are controlled by comparing the deflection voltages with the addresses mentioned (from the control word), converted to analogue form and corrected by adding the contents of vertical and horizontal calibration flip-flops, also converted to analogue form. Termination at line-end can only occur after completion of scanning of a character. Since a line of characters can be oriented along or transverse to the direction of movement of the document, the rotation bit mentioned is provided to cause interchange of the horizontal and vertical deflection voltages and inversion of one of them, when appropriate. The document bears two L-shaped calibration marks, at 90 degrees to each other, for the respective two character orientations. Calibration, when ordered by the control word, involves setting the vertical and horizontal calibration flip-flops in accordance with the vertical and horizontal distances from a start position (specified by addresses in the control word-see above) to the respective bars of the L. Calibration of the dimension transverse to the document is done first, the rotation bit indicating whether this is horizontal or vertical. Each dimension is calibrated by performing 12 scans from the start position across the respective bar of the L. The calibration flip-flops when set make binaryweighted contributions to the correction voltage (i.e. the voltage used for correcting the address or addresses from the control word, though this correction is prevented during calibration). In calibration, the flip-flops are set in turn, in order of decreasing binary significance, one before each of the 12 scans, being reset again if the scan crosses the bar of the L while the deflection voltage is less than the current value of the correction voltage. Scanning of a line of characters (in response to a control word) is followed by scanning in an aging mode until a new control word arrives.