Patent GB-971502-A (GB)
Title: Improvements relating to character reading
Inventor: INGHAM WILLIAM ELLIS
IPC: G06V30/10
Filed: 1959-11-27
Abstract: 971,502. Automatic character reading. ELECTRIC & MUSICAL INDUSTRIES. Nov. 25, 1960 [Nov. 27,1959], No. 40313/59. Heading G4R. In a character reading apparatus a character is sensed in a series of vertical scans to derive black and white signals;signals in each scan are "merged" with signals from previous scans recirculated in a shaft register so that once a black signal has been detected in any horizontal line the register stores a subsequent black signal for that line. The character which moves to the right during sensing is therefore in effect filled in as shown in Fig. 3a. At a position arbitarily selected as centreline of the character the shift register is reset and the process repeats in the second half as shown in Fig. 3b. The character is identified by the groups of black signs Fig. 3c stored at the centre line and the end positions, by the signals derived by scanning the centre line and by a special circuit which detects an indentation in the right hand edge of the character as in "3" or "8". Other features may also be used e.g. whether the top or bottom edge is flat or rounded. The character is moved under a sensing device 6, Fig. 9 comprising a cathode ray tube producing a vertically moving light spot so that the scanning is performed in a vertical raster. The signals derived are amplified at 8, clipped at 9 to binary form and applied to a circuit 10 which rejects short pulses or isolated black signals. The output from circuit 10 is applied to the shift register 11 to which shift pulses are applied to enter into the store a series of "1"s and "0"s for black and white respectively, the register holding exactly one scan. A loop 12 through inhibit gate 13 causes the contents of the store to recirculate synchronously with the entry of sensed data, a "1" where present on either input causing "1" to be stored in the corresponding- register position so that once a black signal has been found in any line, it is retained and the character fills in as in Fig. 3a. The output from circuit 10 also passes via gate 17 which is open for two scans and inhibit gate 21 to set a trigger 20 and thereby a a second trigger 23 to inhibit gate 21. The trigger 23 is reset at the end of the scan by a scan signal from the timing circuit 7. When the trigger 20 is reset by a "0" signal a further trigger 22 is set. The arrangement is such that when a 101 sequence occurs in two successive scans the trigger 22 provides an "indent" signal on its output a. Otherwise a "no indent" signal appears on terminal b. The output from circuit 10 also pass via an inverter 24, in which "1"s are converted to "0"s and viceversa, to a circuit which finds the centre-line of the character. This is arbitarily taken as four scans after the first black-white transition. In the character "2" this occurs in the upper right hand part on the inside of the curve. Adjacent scans, one from inverter 24 and the other from store 11 are gated together at 25 and the first black-white transition through delay unit 26 sets trigger 27. A black signal from store 11 and a white signal from circuit 10 appear in the next scan to cause a further output from gate 25 to pass through gate 28 (enabled by trigger 27) to set trigger 29. On being reset this passes a signal to a counter 32 which counts, in successive scans,four black-white conditions and gives a centre-line signal at its output. Gate 13 is opened by this signal so that the progressive accumulation of "1 "Sin the register ceases and the second phase of operation begins. The centre-line signal also opens And gate 36 to allow the contents of the register to pass to a counter 41 via trigger 40 which enters the first group on the "add" input of the counter and the second group on the subtract intput. The second group of pulses is thereby subtracted from the first and the result positive or negative indicates that the white gap in the stored signals at the centre-line is nearer the bottom or nearer the top of the character. These outputs are stored on triggers 47,49 and are available as voltages on terminals e and d. If there is no gap an output is produced on terminal c indicating that the register contains a solid black line. When the centre-line signal appears a trigger 34 is set and a resetting signal applied to trigger 55 so that gate 56 may pass the signals emerging from circuit 10 and representing the scan coinciding with the centreline. These signals pass to a counter 60 which counts the number of groups of black signals i.e. the number of black parts cut by the centre-line scan. Circuit 61 reduces this number by one to derive the number of white gaps and gives outputs on terminals f,g,h for one, two or three gaps. After the second half of the character has been scanned and stored the end of the character is detected by a circuit beginning at gate 64, which responds to the occurrence of two adjacent all white scans to set trigger 70. This opens gate 71 to allow the contents of register 11 to pass to the counters 41 and 60. In counter 41 the number of "1"S in the register are subtracted from the value already in the counter from the centre-line operation where this value represented a signal black line without gaps. The results on terminals l and m therefore represent that at the centre-line the stored pattern in register 11 was a single group of black signals and that the vertical length of this line is shorter or longer than the line finally stored in the register. All the outputs a-m are gated together in a diode matrix Fig. 10 to produce inhibiting signals on gates 87-96 so that only one of output leads 97 carries a signal. The various features extracted on terminals a-m and others if necessary may be combined in a recognition circuit which gives each a weighting according to its relative importance.