Patent GB-1172463-A (GB)
Title: Character recognition apparatus
IPC: G06V30/146
Filed: 1968-06-20
Abstract: 1,172,463. Character recognition. NATIONAL CASH REGISTER CO. 20 June, 1968 [7 July, 1967], No. 29369/68. Heading G4R. In character recognition apparatus, an indication of the presence or absence of at least part of a character is obtained in response to the degree of continuity in a two-dimensional region, of elemental areas which contrast sufficiently with the background. The character pulse-train from a vertical raster scan of the character, after limiting, is shifted into a 40 by 20 matrix of flip-flops (having one column per scan line) entering at the bottom left-hand corner, say, and shifting up each column in turn. A region of adjacent flip-flops in the left half of the matrix in rows 16-24 is provided with an array (shown in Fig. 10) of logic blocks, each logic block (shown as diamond-shaped in Fig. 10) corresponding to a respective flip-flop. Each block is enabled by the set state of its respective flip-flop to pass a 1 on any of its inputs shown in Fig. 10 (except those from G 1 , G 2  or G 3  if present) to all its outputs. Block 20-1 has no inputs shown and produces a 1 on all its outputs in response to the set state of its corresponding flip-flop alone. In each bit time when this latter flip-flop is set, therefore, 1's will propagate through the Fig. 10 array from block 20-1. The number of blocks passing 1's to their outputs is a measure of the continuity of the " image " in this region of the flip-flop matrix, and if this number exceeds a threshold as determined by a summing amplifier feeding a threshold detector, a control flip-flop is set to indicate the presence of character as distinct from noise. The control flip-flop can be set at any bit time and is reset at the beginning of each scan line. The threshold level used in the threshold detector, is one of three selected according as the original character pulse-train (before limiting) indicates high, medium or low contrast. In the cases of low and medium contrast, character breaks are handled as follows. After the first scan line in which the control flip-flop is set (character beginning) the state of this flip-flop is entered in inverse form, at the end of each scan line, into a 3-stage shift register which is shifted by one stage every scan line. The set states of the three stages (flip-flops) FF 5 , FF 6 , FF 7  thereof enable respective gates G 1 , G 2 , G 3  in Fig. 10 to permit the logic blocks they are connected to (see Fig. 10) to pass 1's from inputs to outputs even if the corresponding flip-flops in the matrix are not set. A character end signal is produced after 1, 2 and 3 consecutive scan lines in which the control flip-flop is not set, in the cases of high, medium and low contrast respectively, with the aid of the 3-stage shift register in the latter two cases. The character end signal prevents further shifting into the flip-flop matrix, but causes horizontal and vertical repositioning of the character " image " in the matrix to put it in a standard position. Horizontal registration is according to whether contrast was high, medium or low since this determined how many consecutive scan lines had to fail to set the control flip-flop before the character end signal was produced. After the first setting of the control flip-flop (character beginning), the number of bit times in each scan line prior to setting of the control flip-flop was counted, the smallest count being retained and used for the vertical registration. Recognition now follows. Clock pulses are produced from a magnetic drum associated with the scanner. Specification 985,399 is referred to for details of the recognition itself, and for an alternative scanner giving character-shaped scans.