Patent GB-1156229-A (GB)
Title: Character Scanning Apparatus
IPC: G06V30/146
Filed: 1966-10-28
Abstract: 1,156,229. Centring character scanner. INTERNATIONAL BUSINESS MACHINES CORP. 28 Oct., 1966 [24 Nov., 1965], No. 48333/66. Heading G4R. Scanning apparatus comprises means for scanning a character and obtaining binary data signals each representing only the presence or absence of an element of the character in a respective segment, defined independent of the character, of the scan field, means for modifying the data signals in accordance with a predetermined criterion independent of the character and comparison means for comparing the modified data signals and providing an output signal which tends to centre the scan field with respect to the character. A flying-spot scanner can scan a document in a vertical raster with either of two horizontal spacings, feeding the scanned bits to a shift register. Initially the wide spacing is used travelling rightwards (mode 0) to locate the first character of a line of characters. Detection of two consecutive black bits in the first two stages of the shift register at any time during a vertical scan indicates the character has been reached and causes the narrow spacing to be used, continuing rightwards (mode 1). During this mode, used for centring the scans vertically on the line, the contents of the first four stages of the shift register are sampled at appropriate times during each scan to set latches on meeting the so-called top, centre and bottom conditions and to increment/decrement a threshold counter, the latches and counter being reset after each scan. The top condition is met if black bits are detected in bit positions 6 and 7, or 7 and 8, in the scan. The centre and bottom conditions relate similarly to positions 11-13 and 23-25, respectively. The threshold counter is decremented by 1, 1 and 2 in response to black bits in scan positions 2, 3 and 4, respectively, and incremented by 2, 1 and 1 in response to black bits in scan positions 27, 28 and 29, respectively. At the end of the scan, the vertical position for the next scan is lowered by one bit position if either the count is equal to or greater than + 1 or the top and centre conditions have not both been satisfied. The vertical position is raised by one bit position if the top and centre conditions have been satisfied and either (a) the count is less than or equal to -1 or (b) the magnitude of the count is less than 1 and the bottom condition has not been satisfied. If the magnitude of the count is less than 1 and the top, centre and bottom conditions have all been satisfied, mode 1 ends and mode 2 follows. In mode 2, the wide raster spacing is used, continuing rightwards. The threshold counter is fed as before but is only reset every 7 scans. At the end of every 7 scans, the vertical position for the next scan is raised one bit position if the count is less than or equal to - 2 and lowered one bit position if the count is greater than or equal to + 2. When a pre-printed right margin stripe on the document is reached, mode 2 ends and mode 3 commences. During mode 3 the scanning raster returns leftwards using the narrow spacing, and recognition circuitry responds to the shift register contents to identify every character reached. Vertical centring on the line of characters occurs as in mode 2 except that the threshold counter is fed during the first 15 scans of each character only and the count is used to control centring, and reset to zero, only between characters.