Patent GB-1222657-A (GB)
Title: Improvements in or relating to scanning arrangements applicable to data recognition systems
Inventor: THOMPSON JOSEPH
IPC: G06V10/10
Filed: 1968-03-22
Abstract: 1,222,657. Character recognition. MARCONI CO. Ltd. 19 Feb., 1969 [22 March, 1968], No. 13882/68. Heading G4R. A scanning arrangement, for use in character recognition, comprises two columns of photodetectors, for pre-scanning and scanning respectively, which are scanned along a line of characters, the distance between the columns in the line direction being at least as much as the width of the widest character to be scanned, logic associated with the pre-scanning column determining the beginning and end of each character and passing this information to logic associated with the scanning column. As described, the document is on a drum which rotates past a stationary head holding two columns of ends of optic fibres which lead to photo-cells, to scan each line, the head being moved axially of the drum by one line position between scans of successive lines. Each column is two line-depths long. Pre-scanning logic.-The pre-scan photo-cell outputs from 1 (Fig. 6) are passed in parallel via thresholding at 18 and sampling at 21 and entered in digital form into registers 19, 20, each receiving all. Register 20 ORs each such parallel entry (called a "Y-scan") with corresponding bits of the previous entries to obtain a " shadow " projection of the tops of the first line of characters when the line position above (empty of characters) is being pre-scanned. At the end of this line position, in response to detection of a " black " in register 19 by first line detector 25, register 20 is shifted out to the right and the number of shifts to shift out the shadow is counted by a Y-scan blanking " circuit 28. This count is saved throughout proscanning of the rest of the document and by copying it non-destructively into a second counter which is then decremented, used to blank off the corresponding portion of each Y- scan entered into registers 19, 20 by control of the rightmost stage during shift-out to the right which occurs after each Y-scan entry. The data shifted out of 19 is lost but that from 20 is reinserted (recirculation). The register 20 is now reset after each confirmed character end. Circuits 26, 27 respond to the contents of registers 19, 20 to detect possible character ends and confirmed character ends, the latter being in response to a more stringent requirement than the former present for 3 consecutive Y-scan entries. A start of character circuit 24 detects character start from register 19. Counters 29, 30, 33 count Y-scans, and counters 34, 37 count shift pulses, being started and stopped as shown, e.g. 34 is started by possible character end and stopped by confirmed character end, counters 29, 33 each providing an output pulse after a predetermined count, and counters 30, 34, 37 are gated at 31, 35, 38 as shown to stores 32, 36, 39. Counter 34 is also reset after each Y-scan entry in which a possible but not a confirmed character end is detected (connection from clock 22 for this, not shown). Accordingly, counters 29, 30, 33, 34, 37 respectively provide to the scanning logic: character start (i.e. character now arriving at the scanning column), character width, character end, character height and vertical position of bottom of character. If the distance between the pre-scanning and scanning columns is large, counters and stores at the bottom of Fig. 6 are duplicated and used cyclically.