Patent GB-1209361-A (GB)
Title: Character recognition apparatus
IPC: G06V30/146
Filed: 1968-02-26
Abstract: 1,209,361. Character recognition. INTERNATIONAL BUSINESS MACHINES CORP. 26 Feb., 1968 [28 Feb., 1967], No. 9109/68. Heading G4R. _ Character recognition apparatus performs a main scanning cycle, comprising a recognition scan of one character interleaved in time with a registration scan of another, data from the registration scan controlling a subsequent main scanning cycle. Vertical and horizontal deflection voltages for flying-spot scanner 22, 24 are supplied by respective integrators 52, 54. The scanner beam is positioned at the right hand end of a line of characters, then the beam executes a curlicue pattern progressing horizontally leftwards until the first character (2 in Fig. 3) is encountered when the flip-flops 64, 66 are reset to release resettable amplifiers 30, 28 to follow the deflection voltages (minus the curlicue, filtered off at 70, 68) which they do as if the voltages were zero when release occurred, i.e. they specify the subsequent changes. The curlicue follows round the outline of the character, positive movements of the vertical and horizontal amplifiers 30, 28 being followed and held by track-holds 144, 104 respectively. After the character has been followed round once, the track-holds 144, 104 hold voltages representing the top and right edges of the character respectively, these voltages being applied via switches 148, 102 to vertical and horizontal potential dividers 94, 92, tapped voltages from which are applied to a normalization matrix 32 as in Specification 1,013,036 to specify a matrix subdivision of the character. The scanner now performs the path consisting of straight line segments 1-13 shown in Fig. 3 under control of gating logic 72, for recognition of the first character and registration of the second, the points at which to change from one segment to the next being indicated by comparison of the vertical and horizontal deflection voltages (from amplifiers 30, 28) with voltages tapped from the voltage dividers 94, 92. The comparisons are done by voltage discriminators 82-91 (Fig. 2A, left) except where otherwise stated. When during scan segment 2, the beam reaches the centre of the first character, discriminator 108 (Fig. 2B) produces a start-of-vertical-scan signal from OR 112. This signal resets the horizontal amplifier 28 to ground, locks the horizontal centre in voltage divider 92 to ground via switch 114, sets flip-flop 168 (Fig. 2A) and resets flipflop 178. When the character is encountered in scan segment 3, threshold detector 98 sets flip-flop 178 which reverses the current state of flip-flop 183, resets flip-flop 146, and causes one of flip-flops 190-192 to be set by gates 170-172 according to whether encounter of the character has occurred in a top, middle or bottom portion thereof. The gates 170-172 are controlled by the voltage discriminators 88, 90 for this purpose. Flip-flops 193-195 and gates 173-175 perform the same function. Assuming that flip-flop 183 was in state 0 and is switched to 1 on encounter of the character, track-hold 184 was following the vertical amplifier 30 but is prevented from changing when flip-flop 183 is set to 1. The voltage in track-hold 184, representing the top of the character, is passed to vertical voltage divider 94 (Fig. 2B), with or without correction by a voltage divider 185 (Fig. 2A) depending on which of the flip-flops 190-192 was set, the flip-flop closing one of switches 150-152 via ANDS 160-162. Had the flip-flop 183 been in the opposite state when encounter of the character occurred, track-hold 186 and associated circuitry (bottom of Fig. 2A) would have been used for the same purpose instead. Two sets of circuitry are thus provided, each used during alternate scan segments 3. At the end of segment 3, flip-flop 66 is reset to release horizontal amplifier 28. During segment 6, while the scan is to the left of the first character (as indicated by voltage discriminator 120 controlled from the horizontal voltage divider 92 and the horizontal amplifier 28), track-hold 126 (Fig. 2B, top) follows the horizontal amplifier 128 until the second character is detected (which sets flip-flop 122). During segment 10, track-hold 128 functions like trackhold 126 in segment 6. Voltage discriminator 130 controls switches 132, 134 to pass the larger of the voltages in track-holds 126, 128 to voltage divider 138. This voltage represents the horizontal position of the rightmost encounter with the second character (6 in Fig. 3) during scan segments 6 and 10. The voltage divider 138 supplies a voltage representing the horizontal centre of the second character to voltage discriminator 142. Vertical misregistration of the second character too great for the above arrangements to correct for is detected during scan segments 4 and 12 when detection of a character will set a flip-flop 214. Horizontal misregistration too great for the above arrangements to correct for is detected if the second character . is not encountered during scan segment 6 or 10 in which ease a flip-flop 204 will remain reset. In either event, OR 206 causes segment 13 to be followed by a segment 14b in which the beam moves down until it reaches the middle position specified by the vertical voltage divider 94, then the beam executes a horizontally progressing curlicue until the second character is encountered, then follows it round as with the first character of the line. On the other hand, in the absence of an output from OR 206, segment 13 is followed by segment 14a which is horizontal movement to the left until the horizontal centre of the second character is reached when voltage discriminator 142 (Fig. 2B) produces the startof-vertical-scan signal from OR 112 which causes scanning of the second character to start with segment 3.