Patent GB-1020647-A (GB)
Title: Character reader
IPC: G06V10/24
Filed: 1964-01-09
Abstract: 1,020,647. Automatic character reading. RADIO CORPORATION OF AMERICA. Jan. 9, 1964 [Jan. 25, 1963], No. 1037/64. Heading G4R. In an optical character reading apparatus for reading characters each having a distinctive arrangement of vertical strokes, there are means for dividing the character into a plurality of zones in accordance with the detection of vertical strokes and means for storing signals relating to each zone of the character in a separate store. The numerals, Fig. 3, are formed of a series of vertical and horizontal strokes. Characters are scanned by a flying spot scanner or a camera tube making a series of vertical scans over the character. The scans are long enough, as shown in Fig. 2, to cover the character even when it is badly displaced. About 10 scans cover a character and about 14 sample times in each scan. The character strokes vary in thickness according to the heaviness of printing. As shown in Fig. 6, a vertical stroke may occupy one scan, two scans or more than two scans according as to whether the character is " light," " nominal " or " heavy." As shown in Fig. 3 all the numerals have a vertical stroke on the right-hand side. There are four other symbols, two of which have a central vertical stroke and a dash-and-dot which are distinguished by their height. The character area is divided into zones 1, 2 and 3 as shown in Fig. 4, the division lines being non-fixed. If the vertical stroke lines of a character are thin zones 1 and 3 are correspondingly narrow. In Fig. 2, zone 1 occupies two scans, zone 2 six scans and zone 3 two scans. In Fig. 6d the zones have 4, 3 and 3 scans, respectively. Video signals from the scanner are applied with clock pulses to a group of four flip-flops forming a shift register. The outputs of the register stages are gated together so as to ignore single white signals and applied to a vertical stroke detecting circuit in which the signal is delayed and gated with itself. An output indicates a medium vertical stroke, i.e. a stroke as in character " 2 " lasting more than five sample times. The signal is passed back again through the delay to derive an indication of a long vertical stroke. The output of the vertical stroke detector controls a scan counter the output of which indicates that the vertical stroke has been detected by one scan or by two or more than two successive scans. This indication is stored as an indication that the type of character is light, nominal or heavy. A counter is provided for counting the number of scans made on a character, the counter being started either by a second scan with black signals (this ignores spurious marks) or by certain combinations of black and white signals stored in a later shift register representing particular shapes. Other particular shapes are taken as representing spurious marks and do not start the scan counter. The zoning circuit receives signals from the " type of character " indicator, the vertical stroke detector and the scan counter. The zoning circuit changes from zone 1 to zone 2 when a scan arrives in which the first vertical stroke no longer appears or after a predetermined number of scans. The change from zone 2 to zone 3 depends upon the type of character, the number of scans already made in zone 2 and whether or not vertical strokes are detected. Successive outputs on three leads represent the three zones and control the entry of the video signals into two further shift registers each having 21 stages. The signals from scans in zone 1 enter the first and signals from zone 3 (and sometimes zone 2) enter the second. Outputs from the first register are gated together to provide the start signal, mentioned above on the scanning of certain predetermined shapes. Each register has a feed-back loop designed to cause black signals arriving in successive scans during a zone to be retained. This fills in white spaces in the strokes and also compensates for skewing of the characters. At the end of the scanning of a character the contents of the two registers are shifted so as to bring the signals to a predetermined position. The actual vertical position of the character in the scanned area, Fig. 2, is therefore not important. Outputs from the two shift registers are gated together to provide signals indicating the presence of vertical strokes in the right or left, upper or lower parts of the character (Fig. 4) and also the overall height of the character. The height is used to distinguish the symbols from the numerals and from each other. During the middle zone other feature elements are extracted. The number of black crossings encountered in each scan during this zone is counted. The counter output, a signal on one of three leads passes to a corresponding one of three counters so that at the end of zone 2 each counter holds a count of the number of scans finding single, double or triple black crossings respectively. To compensate for defects of printing the highest count is found by a comparator and the output, a signal on one of three leads, indicates that the majority of scans made, say three black crossings (for character " 2 "). Another circuit operative in zone 2 counts the number of sample pulses occurring during the time a scan is crossing from one black crossing to another. This produces a short or long " white gap " signal. Another circuit receives the signal from the vertical stroke detecting circuit and the zone 2 signal to indicate the presence of a central vertical stroke. All these feature signals are passed to a recognition circuit consisting of an array of diodes or gates and the signal indicating the character scanned is decoded if necessary and passed to an output circuit, e.g. a store or a computer.