Patent GB-1350200-A (GB)
Title: Optical character recognition arrangements
IPC: G06V30/10
Filed: 1970-11-30
Abstract: 1350200 Character recognition systems PLESSEY CO Ltd 23 Nov 1971 [30 Nov 1970] 56871/70 Heading G4R A character recognition apparatus includes a two-dimensional array of light sensors which sense the character. The rows are scanned in turn, and parallel outputs taken from the columns. The amplitude of a signal on any one column output corresponds to the light sensed by the sensor in the currently scanned row. Two or more of the column outputs are connected to comparator circuits which detect the presence of vertical or horizontal edges or strokes in the character.  The following description assumes that a character, or the image of a character, in OCR-A font is on a matrix of 5 columns and 72 rows of elements. The columns are scanned vertically upwards simultaneously. To detect a vertical edge of the character any one or more of the following circuits is used. Fig. 7A: The signals X, Y resulting from the scanning of two adjacent columns are fed to comparator 131. If for example, signal X is high representing black and signal Y is low representing white, comparator 131 outputs a 1-bit. The comparator feeds integrator 132 and counter 138. If the integrator output exceeds a value set by unit 136 comparator 135 outputs a 1-bit indicating that a vertical edge has been detected. Counter 138 resets the integrator only if comparator 131 gives a 0-bit for at least 5 successive rows of the matrix, i.e. if there is a long white gap in column providing signal X. Shorter gaps do not cause resetting. so a small void in the edge does not prevent recognition of the edge. As there are 4 pairs of adjacent columns 4 circuits as described above are provided. Fig. 7B (not shown): the circuit of Fig. 7A is augmented by a second comparator (139) whose output, together with that of comparator 131, is fed to the integrator and counter via an OR gate (140). The second comparator is fed with signal X direct, and with signal Y via a delay equivalent to the scanning of adjacent rows. An element in column 2, for example is therefore compared both with that in the same row of the adjacent column 1 and with that in the preceding row in the adjacent column 1. Fig. 7C (not shown): Here signals from columns 1, 2 and 4 are used. Each element x in column 1 is compared with element x and element x-1 in columns 2 and 4. The comparators feed an OR gate feeding the integrator as in Fig. 7A. Fig. 7D (not shown): Signals from 3 adjacent columns are compared. For example, each element in row column 3 is compared with element in columns 2 and 4, the comparators feeding an OR gate as before. To detect a vertical stroke of one column width a circuit, Fig. 7E (not shown), is used. This is identical to that of Fig. 7D except that the OR gate is replaced by an AND gate. To detect a horizontal edge, signals in 3 adjacent columns are used, e.g. as in Fig. 9B, or Fig. 9C (not shown). Signals corresponding to element x in the 3 columns pass to unit 173 which develops a signal corresponding to the least black of the three elements. Signals corresponding to element x - 1 in the columns are compared in pairs in units 183-185. Two of these develop a signal corresponding to the least white and one a signal corresponding to the next-least-white of the three elements. These signals are compared at 175-177 with the least-black signal. If the least-black is blacker than the said next-least-white, at least one of comparators 175-177 provides an output indicating the presence of a horizontal edge. To detect a horizontal stroke one element row wide, circuits as in Fig. 10B or 10C (neither shown) may be used. Here elements x in 3 adjacent columns are fed to a unit to determine the least-black signal. Various of the elements x+1 and x-1 are compared to determine least-white and next-least-white signals, these being compared with the black to determine the presence or absence of the stroke. The circuits described above must be modified if the vertical edge to be detected is that to the right of a vertical stroke, or if the horizontal edge is that above a horizontal stroke.