Patent GB-1274593-A (GB)
Title: Character recognition
IPC: G06V30/10
Filed: 1970-05-07
Abstract: 1,274,593. Character recognition. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 7 May, 1970 [10 May, 1969], No. 22066/70. Heading G4R. A device for use in determining the centre lines of the strokes of a character has means for scanning the character in at least two mutually transverse directions, for determining on each scan line one or more intersections with the character, and for determining the centres of the intersections. In Fig. 2, a counter T 1  driven by a clock generator Cl produces pulses OT 1 , OT n  alternately. Each pulse OT 1  starts a sawtooth generator 1, and each pulse OT n  resets it, increments a step generator 2 and increments a scan line counter T 2 . The generators 1, 2 provide a horizontal raster for an electron-beam scanner 4, 5, then a vertical raster, the changeover occurring when counter T 2  reverses a flipflop FF to interchange the voltages supplied to the scanner. Detector 6 produces a pulse at 7 at each white-to-black transistion in the video from the scanner and a pulse at 8 for each blackto-white. The pulses at 7 and 8 respectively start and reset a sawtooth generator 9, the sawtooth having half the slope of that from generator 1 but being in the opposite direction. The two are added at 10. Alternatively, if the sawtooths are in the same direction, a subtractor is used at 10. Each pulse at 8 gates out 11, 12 to an oscilloscope display, the voltages from 10, 2 which represent the positions of the centre of the intersection of the scan line with the character stroke. The character can be recognized using logic from the thinned version on the oscilloscope, or (Fig. 4, not shown) the output of gate 11 may be digitized and stored in a register with the current setting of the flip-flop FF and the count of counter T 2  (gated by the pulse at 8), or the output of gate 12 may be digitized and used in place of the count from T 2 . The contents of the register are passed directly or via a store to recognition logic. Alternatively, the count of counter T 2  may be used to address this latter store to store the digitized output of gate 11. Another embodiment (Fig. 5, not shown) drives a further counter from generator Cl directly when the video from the scanner is white and via a frequency-halver when it is black, and gates out the counter at each black-to-white transition, the counter then being reloaded from counter T 1 . The count of counter T 2  and the state of the flip-flop FF are also taken, as before. This embodiment may be modified (Fig. 6, not shown) by supplying the video black and white signals to control driving of the further counter (see above) via a circuit using delays, a trigger and gates, so that short blacks and whites are ignored. A black-to-white transition is also prevented from effecting its usual functions (see above) if the black just ended integrates to above a threshold: thus line centres measured in the direction of the length of a character stroke are ignored. The two rasters may be performed by respective scanners simultaneously, or scanning may be by addressing a core matrix in which the character is first simulated.