Patent GB-1390459-A (GB)
Title: Recognition unit for optical character reading system
IPC: G06V10/20
Filed: 1972-03-29
Abstract: 1390459 Character recognition systems RECOGNITION EQUIPMENT Inc 29 March 1972 [28 July 1971] 14780/72 Heading G4R A character recognition system includes a column of photo-sensors which is scanned over the characters and from which signals representing black and white areas of the character field are developed. The signals are applied to circuitry simulating black and white character masks and the mask outputs are compared with a reference signal. If any mask provides a signal above the reference the corresponding character is indicated. The character to be recognized passes beneath a scanner comprising an oscillating mirror and a column of photo-cells. The column (81, Fig. 3, not shown) is tall enough to scan a region above and below the character to accommodate misregistration. The outputs of the cells are quantized to 15 levels (4 bits) and normalized (82, 83) and are fed via first and second shift register stores (84, 85) to the circuit (86), Fig. 4 (not shown), which determines the black/white state of each area of a matrix of areas covering the character field. Signals each representing the blackness of a given elementary area of the matrix are processed with signals representing areas surrounding the given area to determine whether the area is to be considered as black or white. As disclosed the signal from the given area is multiplied by 25, this being the number of areas in a 5 x 5 array of which the given area is at the centre. The sum of the areas is formed and is biased in the black sense by a selectable amount. A relative black signal is generated if the multiplied value exceeds the biased sum. Also an absolute black signals is generated if the signal from the given area is greater than a selected reference value. The given area is deemed to be black if either a relative black signal or an absolute black signal is generated, and is deemed to be white in the absence of these signals. The resulting data is stored (87) and the position of the character in the data field in the store is determined (88 and Fig. 7, not shown). The portion of the field that contains the character is passed to a further store (89) and then via a vertical centralizing unit (91) to another store 92, Fig. 8. 'Store 92 contains data representing the white areas of the scanned character field. The white data is read out in parallel to white mask drivers 93 and via inverters to black mask drivers 93. The drivers are coupled to all the masks. The masks are defined by resistors which may be weighted. Each pair of masks may be combined, e.g. as in Fig. 9. To compensate for vertical misalignment which may have occurred during porcessing the data is shifted vertically twice while the store is connected to the drivers. The outputs of those masks corresponding to a particular font are selected and each is applied to respective threshold amplifier 140. Each output passes via a capacitor store 108 and if any output is sufficiently high OR gate 106 enables staircase generator 107 whose output is compared at 151 with the outputs of amplifiers 140. By counting the steps necessary to reach equality with the output of an amplifier 140 the likelihood of the corresponding character representing the scanned character is indicated by setting bi-stable 152.