Patent GB-1119778-A (GB)
Title: Character recognition system
IPC: G06V10/20
Filed: 1966-02-08
Abstract: 1,119,778. Character recognition. INTERNATIONAL BUSINESS MACHINES CORP. 8 Feb., 1966 [12 Feb., 1965], No. 5558/66. Heading G4R. In a character recognition system, signals from two parallel vertical scans of the character, spaced apart by half the character width, are analysed separately and simultaneously. A slotted-disc scanner 13, 15 scans the character in a series of vertical scans producing a video signal which, after clipping and data reduction (the latter involving ORing the signal with itself one-bit-time delayed to halve the bit frequency), is recorded on a magnet drum 19 driven by the same motor as the scanner. The signal is recorded twice in respective tracks at a relative angular spacing corresponding to one scan length. The tracks are read by two pairs of read heads, Ra, Rb and Rc, Rd, spaced by half a character width. Sync. signals are read from other tracks. The data signals read from the drum at any instant correspond to the same horizontal level in two pairs of adjacent scans, the pairs being called Y and Z scans and being half a character width apart, a given part of the character occurring in a Y scan before a Z scan. The signals from the first pair of read heads Ra, Rb, i.e. Y scan, are compared and the first time they are both black a first Y trigger (YT1, Fig. 3a, not shown) is set, allowing a second Y trigger (YT2) to be set on the next double black. A double white resets the first (YT1), a second double white resetting the second (YT2). While the first (YT1) is set, a Y counter (binary) 31 counts one-bit-time sync. pulses (A sync.), the Y counter being reset when the second trigger (YT2) is reset. Thus the Y counter 31 measures the heights of character strokes, ignoring one-bit voids. A similar arrangement is used for the second pair of read heads, Rc, Rd, i.e. Z scan, but the Z counter 33 has an extra stage enabling the recognition, by a gate connected to Z counter stages, of an extra long special field mark, producing a corresponding signal (SPFM) from a corresponding feature trigger. Other feature triggers are set under control of the Y and Z counters 31, 33 separately, the particular combinations of the counter stages setting the triggers being changeable by a switch (FSW) in accordance with the fount. Most of the feature triggers are reset (ECR) at the end of each scan, until enough data has been obtained for recognition to be attempted, as indicated by an MCR, i.e. minimum character requirement, trigger being set as follows (Fig. 4, not shown). Under control of the lowest order stage (Z1) of the Z counter 33, an inhibit trigger (INHT) is set during an all white Z scan, i.e. before the character, thereby enabling the MCR trigger to be set by the special field mark signal (SPFM) or both the Y and Z counters 31, 33 holding a count of at least one (Y1, Z1) or a signal (ZVM) indicating the presence of a long vertical feature in the Z scan. The MCR trigger will then be reset on occurrence of an all white Y scan, under control of the lowest order stage (Y1) of the Y counter 31, at which time a signal ECS is produced to enable INVERTER and AND logic to recognise the character from the feature trigger setting, a " fail to recognize signal " also being possible. A scan counter (Fig. 5, not shown) is enabled by the MCR signal to count scans, a count of 5 preventing further counting and producing a left signal (LT) indicating that the left side of the character has been reached, a right signal (RT) having been present prior to this. Once the character has been encountered, a chain of triggers (LWRT, CTRT, UPRT, Fig. 4, not shown) is advanced under control of the lowest order stage of the Y or Z counter 31, 33 depending on whether the right or left signal is present, to indicate the current vertical position along the scan. This chain of triggers, together with the left and right signals (LT, RT) and signals (YVM, ZVM) from feature triggers indicating long vertical marks in Y and Z scans, combine to control a matrix of feature triggers (ULT, CLT, LLT, LCT, URT, CRT, LRT) for indicating the presence or absence of vertical marks in seven of the nine areas of a 3 x 3 matrix subdivision of the character. The right and left signals (RT, LT) are also involved in the control of some of the earlier mentioned feature triggers. Triggers are also provided for the open right centre feature (Fig. 6, not shown), the single horizontal feature (1HT, Fig. 3b, not shown) and the three horizontals feature (3HT, Fig. 4, not shown), the trigger for the last being controlled from the chain of triggers (LWRT, CTRT, UPRT) mentioned and its stepping input. " Trigger " is used above to include " latch ". Erase heads are provided on the magnetic drum 19 but may be disabled if a fixed recorded pattern is required for diagnostic troubleshooting. A counter may be used to produce left, centre, and right signals in place of just the left and right (LT, RT) described above.