Patent GB-1281267-A (GB)
Title: Beam scan control apparatus
IPC: G06V30/10
Filed: 1970-05-29
Abstract: 1281267 Pattern recognition INTERNATIONAL BUSINESS MACHINES CORP 29 May 1970 [2 June 1969] 25964/70 Heading G4R A beam scan control apparatus comprises a detection unit responsive to command signals representing characteristics of a scan format and providing control signals indicative of the position of the beam relative to all the boundaries of the format, a boundary ("margin") control unit responsive to the control signals to indicate the position of the beam relative to selected ones of the boundaries, and a scan selector unit for scanning the beam in a sequence of scan modes in order to scan over the format represented by the command signals. In the detection unit, a latch is set by a LOAD signal from a CPU channel and reset by a TERMinate signal from the boundary control unit. While set the latch permits a counter to be incremented by pulses accompanying the bytes of a 4 or 8 byte format word from the CPU channel, the counter, via a decoder, gating the bytes into respective registers as they arrive. The counter decoder sends a signal to the scan selector unit in the case of more than 4 bytes. The bytes specify respectively (1) a first horizontal boundary, (2) a first vertical boundary, (3) a second horizontal boundary, (4) the symbol set to be recognized together with the orientation (horizontal or vertical) of the symbols on the document, (5) a second vertical boundary, (6) a third horizontal boundary, (7) a third vertical boundary, (8) whether the left or right boundary of the field is to be indented. The four byte case uses bytes (1)-(4) only. The bytes other than (4) and (8) are converted to analogue form and compared with horizontal (i.e. parallel to the line of symbols to be read) and vertical deflection voltages of a flying-spot scanner to indicate variously to the boundary control unit and the scan selector unit when the scan is to the right of the first and third horizontal boundaries, to the left of the second and third horizontal boundaries and two auxiliary boundaries (one inch to the left of the first and third horizontal boundaries respectively) and below the first, second and third vertical boundaries, separately. Bytes (4) and (8) are decoded to supply the symbol set indication to a recognition unit, the orientation indication to the flying-spot scanner (to interchange the horizontal and vertical deflection voltages or not), and the indentation indications to the boundary control unit. The boundary control unit, during a line search mode, uses the below second and third vertical boundary signals to set and reset a latch respectively, to indicate vertical position, the below third signal also producing the TERMinate signal (indicating field end) which is also supplied to the CPU channel and the scan selector unit. The vertical position indications just mentioned are used in conjunction with the signals indicating the left and right of horizontal and auxiliary boundaries from the detection unit, in dependence upon the indentation indications, to indicate when the beam is to the left of the left margin of the field, to the right of the right margin, and to the left of an auxiliary margin, separately. These indications go to the scan selector unit, and the left of left margin signal also goes to the CPU channel. The scan selector unit which also receives digitized video from the scanner, and READ and LOAD signals from the CPU channel, causes the beam, in the case of an 8-byte format word, to move to ("seek") the intersection of the right margin and the first vertical boundary, then to search for a line by performing a horizontal raster between the right and auxiliary margins. When black video is encountered, the beam moves down 40 mils and to the right margin, then a leftwardsprogressing vertical "character search" raster is performed. If the auxiliary margin is passed during this, line search is resumed since the black video encountered was presumably dirt or ink splatter. Detection of black video during "character search" initiates a normalization scan as in Specification 1,269,140 (referred to), after which the beam is initialized to the right margin, to avoid missing any small characters missed previously. A recognition scan as in Specification 1,209,361 (referred to) then follows. When the left margin is passed, the beam idles in a holding pattern. A symbol may be re-read by sending the READ signal alone, which causes operation to commence again but starting at the normalization scan. LOAD followed by READ (excluding a new format word) causes operations to start at the line search scan, to find the next line. The TERMinate signal, produced on reaching the bottom of the field, initiates an ageing scan, as in Specification 1,172,789 (referred to). The recognition unit receives the digitized video from the scanner, and supplies its output to the CPU channel.