Patent GB-1281268-A (GB)
Title: Beam scan control apparatus
IPC: G06V30/10
Filed: 1970-05-29
Abstract: 1281268 Pattern recognition INTERNATIONAL BUSINESS MACHINES CORP 29 May 1970 [2 June 1969] 25965/70 Addition to 1281267 Heading G4R Scan control apparatus for controlling the scanning of a beam is responsive to format command signals and provides control signals indicative of the position of the beam relative to at least some of the boundaries of the format, and is responsive to the command and control signals to scan the beam in a sequence of scan modes in order to scan over the formats represented by the command signals, one boundary of a format being scanned being defined using the stored position of a scanned pattern recognized by pattern recognition apparatus. A flying-spot scanner feeding digitized video to a recognition unit which supplies its result to a CPU channel, is controlled by successive format words from the CPU channel. A format word has bytes to specify the beginning and end horizontal positions (except that if reading is left to right, (see below), the actual field beginning is one inch to the left of the "beginning, position specified) and the top boundary vertical position of the field to be scanned (all converted to analogue form) and other field information (decoded to indicate the character set to the recognition unit, the direction of reading i.e. left to right or right to left, whether or not the horizontal and vertical deflection voltages should be interchanged i.e. orientation of the characters on the document, whether or not the scanning is to be in an "unformatted-field" mode i.e. confined to a preselected area or "unformatteddocument" mode i.e. scanning the whole document subject to time-saving devices mentioned below, and whether a group erasure mark if present on the document is to be ignored). A subsequent format word may specify the bottom vertical boundary position of the field instead of the top, the new top being defined by the vertical position of a line just read by saving the digitized version of the scanner vertical deflection voltage in a line-storage unit. This digitization is done by setting each bit position in a register to 1 in turn, and after each bit is so set, converting the register contents to analogue form, comparing them with the deflection voltage, and resetting the bit to 0 or not according to the result, before setting the next register bit to 1. The analogue boundary voltages derived from the format word, and voltages derived from them by resistor voltage dividers, are compared with the scanner horizontal and vertical deflection voltages, to indicate (separately) when the scanner beam is to the right of the beginning boundary, to the left of an auxiliary boundary one inch to the left of this boundary (these two indications being interchanged if the direction of reading is left to right), at the line end, at the bottom of the read window, at the vertical boundary specified by the format word, and at an auxiliary boundary one inch below this boundary. After loading of the first format word from the CPU channel, which also supplies a LOAD FORMAT command, then if either cf the two "unformatted" modes is required, a READ command from the CPU channel is provided to cause the scanner beam to perform a horizontal raster from the top of the field between the beginning (horizontal) boundary and its auxiliary boundary ("seek" and "line search"). When black video is encountered ("strike") the beam is moved down 40 mils and then back and forth once between the beginning and auxiliary boundaries, a "long black detector" sending a document end signal to the CPU channel if the amount of black encountered indicates the scan is now on the dark bed plate on which the document rests. If this does not happen, a vertical raster moves along the line reached to search for a character. "Line search" is resumed if the beginning or auxiliary boundary (whichever is further along the line) is passed, since this indicates that the "strike" was on dirt or ink splatter. If a character is encountered before this happens, a normalizing scan as in Specification 1,269,140 (referred to) is performed. If a group erasure mark is encountered and is not to be ignored, "line search" is resumed, whereas if the detected video is of less than a predetermined height (indicating a small character e.g. period or dash) "character search" is resumed. If neither of these events occurs, the normalizing scan is followed by initializing the beam to the horizontal field beginning and moving it down a small amount, then a small vertical raster follows for recognition. The line-storage unit saves the vertical position sought in initialization. During the recognition scan, detection of continuous white video for two normal character widths by a blank detector causes a high speed skip of the beam (with the same pattern as "character search") until black video is encountered when normalization follows, followed by initialization and recognition scanning (alternatively, normalization, or normalization and initialization, may be omitted). Line end is indicated to the CPU if the end horizontal boundary of the field is passed, or if the high speed skip has continued for 800 mils without encountering black video (indicated by the blank detector). Line end or document end is followed by an ageing scan. The CPU channel may respond to line end by beginning a new field with a new format word e.g. if a required number of lines has been read even though the field has not ended, or send just a READ command which causes "seek" followed by a recognition scan to re-read the line just read, or another format word may be provided to read the next line utilizing the line-storage unit to specify the new field top (see above). In the latter case, if the beam passes below the field bottom specified by the format word (during line search in the "unformatted-field" mode), an end of field signal is sent to the CPU channel and also produces a line end signal. With the first format word which specifies field top, end of field is indicated if the beam moves below the auxiliary boundary associated with this top boundary, during line search (in the "unformatted-field" mode). If the bottom of the read window is reached during line search in the "unformatted-document" mode, an end of window signal is produced unless a document sensor indicates this is the last window in which case the document end signal is produced. The end window signal causes the document to be incremented, and the beam to ride up with it by performing a raster as in "line search" but moving the beam up rapidly by 10 mils on detection of black video. When the document is in place at its new position, "line search" &c. follow as before. In a modification, "strike" is taken to occur only when two (rather than one) black video hits occur during a single horizontal sweep of the "line search" raster. This prevents triggering by a long vertical mark or a document calibration mark, if present.