Patent GB-1083407-A (GB)
Title: Character reader
IPC: G06V30/10
Filed: 1965-06-22
Abstract: 1,083,407. Automatic character reading. RADIO CORPORATION OF AMERICA. June 22, 1965 [July 20, 1964], No. 26373/65. Heading G4R. A character reader comprises means for securing the characters on a number of parallel lines to obtain video signals, a newly detected stroke in any scan line being classified as a new stroke, if no prior stroke has been detected in that scan line. There are eight vertical scan lines over the character, Fig. 2, signals being produced in each representing intersections with the character, Fig. 3. In scan line SC1 the bottom stroke 34 of the character is cut and a pulse P1 is produced. This being the first in that scan it is designated a new stroke and labelled "A." The video signals are delayed one scan so that adjacent scans can be compared. In scan line SC2 the upper part of the character is first cut giving pulse P2. Since this does not correspond with a signal in the first scan it is designated a new stroke and is labelled " B." Pulse P3 corresponds with pulse P1 of the first scan and is recognised as belonging to stroke A. Similar operations occur in scan line SC3, the long pulse 14 being taken to be part of stroke B as it overlaps the delayed pulse P2 from the second scan. Pulse P5 is again recognised as part of stroke A. In scan line SC4 there are three pulses. The first P6 overlaps with pulse P4 and is as stroke B. The second P7 also overlaps P4 but the gap between it and P6 causes it to be designated a new stroke and it is labelled " C." The fact that it overlaps P4 is taken to indicate that this stroke C starts as a fork from stroke B. The three pulses appear again in the next two scans and are recognized as belonging to the strokes B, C, and A already being tracked. In scan line SC7 the first pulse P15 is recognized as belonging to stroke B and the second is recognized as being the join between strikes A and C, since it overlaps pulses P13 and P14 from the previous scan. The incoming video signals are delayed by the time between two scans and compared with the undelayed signal in a pulse analyser. The signals relating to the adjacent scans are combined in various ways and used to derive signals indicating that a stroke detected is a new stroke, that it is the reappearance of a stroke previously detected, that it has been formed by forking 'from a previous stroke, that it has ended by joining with another stroke, or that it has simply ended on its own. These indications are derived by circuits, Fig. 5, for example a " new stroke " signal is obtained by applying to the set input of a flip-flop 144 a pulse aL appearing at the leading edge of a black signal in the present scan a. In reset input is by a signal a.b indicating that black signals are simultaneously present in both the present and previous scans. The set output of the flip-flop is gated at 146 with the trailing edge signal aT of the black pulse -in scan a. If, therefore, in the interval between the leading edge of a black pulse in scan a and the trailing edge, no a.b signal appears indicating that there is a corresponding black signal in the previous scan, the stroke is indicated as being a new stroke. The flip-flop 144 is reset by an output throngh delay 148. The stroke tracker control generates advance pulses for a counter in a stroke counter and tracker unit. Signals indicating new strokes or forks are applied to the counter through an Or gate. The counter is a four-stage ring so that a maximum of four strokes can be accommodated. For each possible stroke, there is a three stage store, the four stores being interconnected to form a shift register. The letters A, B, C D are represented by binary digits 01, 10, 11 and 00. When a stroke ends, by join or end, a "1" is entered in the third stage so that "101" indicates that the stroke A is entered in that store and that it is retired. Initially the letters A, B, C ,D are entered in the four stores, but these become scrambled as tracking proceeds according to the order in which the strokes are detected. The bottom stroke 34 (Fig. 2) is detected in the first scan line and is classified as stroke A. This is indicated as the top stroke (since there are no others) and the order of codes stored remains A, B, C, D. In the second scan line stroke 30 is detected and labelled " B." This is now indicated as the top stroke and the order of codes in the store changes to B, A, C, D. The last two stores -are not yet operative. In scan line SC4 (Fig. 2) the stroke 32 is detected and labelled "C." The order of codes stored is now changed to B, C, A, D since stroke B is still the 'top stroke and D is still inoperative. When in scan line 7 stroke 34 joins with stroke 'C, the first stroke A is retired and a "1" is stored with the "A" code to indicate this. In the next scan line the other two strokes retire. The character determining circuit stores the fact that stroke C started with a fork and stroke A ended with a join and the labels A, B, C are converted to 3, 1, 2 indicating their positions in the character. The character is determined from the combination of these features.