Patent GB-878931-A (GB)
Title: Character recognition equipment
IPC: G06V30/18
Filed: 1959-06-05
Abstract: 878,931. Automatic character reading. STANDARD TELEPHONES & CABLES Ltd. June 5, 1959 [June 6, 1958], No. 19315/59. Class 106 (1). In a character recognition apparatus the characters are scanned along a number of parallel tracks, pulses being produced when changes from white to black are detected there being one group of triggers each of which corresponds to one of the tracks and is set and reset by the pulses from it (each trigger therefore indicates whether the number of crossovers was odd or even) and another group of triggers each of which is set by the pulses from one track and reset by the pulses from an adjacent or nearby track (each trigger therefore indicating the sequence of occurrence of pulses in the adjacent tracks), outputs from the two groups being combined to identify the character scanned. The sensing means used consists of a line of photo-cells such as photo-cell 1, Fig. 1, the output from which is amplified at 2 and digitised at 3 to produce a two-state output at A1 representing either black or white. At terminal A2 a pulse appears whenever a black signal appears on terminal A1. In Fig. 2, two photo-cells 4 are shown, a trigger 5 being connected to the A2 outputs of one and trigger 6 to the A2 outputs of both. Trigger 5 is set or reset by each input pulse and accordingly it counts in a scale of two the number of black lines crossed during the scan, indicating whether the number is odd or even. The trigger 6 is set by a pulse from the upper photocell and reset by a pulse from the lower photocell. The four shape elements a, b, c and d cause the triggers to be set and reset as shown in the thick and light lines respectively. For element a the trigger 6 is uneffected by the resetting pulse from the lower photo-cell as it crosses the edge of the element, but is set with trigger 5 when the upper photocell meets the element. Neither is reset and this element according leaves both triggers set. With element b the triggers set together when the upper photocell encounters the element, but trigger 6 is reset when the lower photocell encounters the second part. The operation with elements c and d is as shown, the trigger 5 indicating whether the number of horizontal cross-overs is odd or even and trigger 6 indicating that the final line of the element slopes up to the right or down to the right. Since in the sensing of a vertical line setting and resetting pulses would occur simultaneously to give an unreliable result, a further terminal A3, Fig. 5, is provided on which appears a resetting pulse which is longer in duration than the setting pulse. For this purpose terminals A2 and A3 are supplied via resistance-capacity circuits with different values. A vertical line causes the corresponding triggers to set and almost immediately to reset. Alternatively, the photocells could be staggered. In Fig. 7, the response of the two sets of triggers 5 and 6 are shown in the upper and lower decks respectively for the digits 1-5. In the upper deck a trigger 6 is "on" for one cross-over and "off" for 0 or two cross-overs. In the lower deck the triggers 5 are controlled by the sequence of signals on next-but-one photocells. Generally a number of adjacent on conditions indicate an upward slope in the last line cut. Certain triggers are unreliable in particular cases. These are marked "U." From both sets of triggers characteristic combinations of signals are obtained and are applied to a recognition circuit in which the character is identified, the circuit for any digit ignoring the "U" lines for that digit. Centring.-Before recognition the stored patterns in triggers 5 and 6 must be in a position which is constant for all characters. For this purpose the triggers of each set are connected together so as to operate as a shift register and the patterns are shifted downwards until the lowest trigger of each set is "on."