Patent GB-1115910-A (GB)
Title: Digital-analog retina output conditioning
IPC: G06K9/64
Filed: 1966-06-07
Abstract: 1,115,910. Character recognition. RECOGNITION EQUIPMENT Inc. 7 June, 1966 [7 June, 1965], No. 25272/66. Heading G4R. [Also in Division H3] A device which can be fed from retina transducers sensing a pattern on a background, comprises means for comparing the output of one transducer with the average of the outputs of a number of transducers in a surrounding area to generate a black analogue voltage and a white reference voltage if said one transducer is in registration with an area darker than the average of the surrounding area, and to generate a white analogue voltage and a black reference voltage if said one transducer is in registration with an area lighter than the average of the surrounding area. The image of a character moves across an array of photo-cells which is rectangular apart from a tail, the signals from a band of photocells containing the top character being selected by a matrix of switches (see Compensation for misalignment below) after amplification with automatic gain-oontrol to compensate for variations in background whiteness, and fed to amplitude correlators, one per selected photocell, to produce the analogue and reference black and white voltages mentioned above which are fed to weighted-resistor masks. Each possible character has a white mask and a black mask, and if a given photo-cell should show black for the given character the latter's black mask receives the white-output line relating to that photo-cell, the line carrying the reference level if the photo-cell actually shows black (or rather blacker than the average of the surrounding twenty photo-cells by at least a bias amount) and carrying the analogue indication of the photo-cell output if the photo-cell shows white. Reverse connections are made if the photo-cell should show white for the given character. The bias referred to is provided by a diode in the (each) amplitude correlator and compensates for slight imperfections of printing or background quality. The mask outputs are amplified with a cut-off to eliminate two of the three peaks produced due to the vertical jitter during the movement of the character (see Compensation for misalignment below). Each amplifier output (one per possible character) is stored on a capacitor and progressively increased by a staircase voltage initiated after a delay by a character presence detector controlled by the amplifier outputs. Any capacitor voltage reaching a threshold sets a corresponding flipflop to identify the character to a computer, the flip-flop setting being utilized only if no other flip-flop is set during a certain interval starting when the first was set. Compensation for misalignment.-The photo. cell outputs of each row of the array (after gaincontrolled amplification-see above) are (separately) ORed and fed to a diode matrix which recognizes the top row of a character by detecting two adjacent rows with at least one black, superposed by two entirely white, and recognizes the bottom row of a character by detecting one row with at least one black, above three adjacent rows entirely white. Inhibit signals are fed-back so that only the top and bottom of the uppermost character are indicated. The position of the centre of the character is calculated from the top and bottom positions by two subtractors and a halver and controls the matrix of switches mentioned previously to select the band of sixteen photo-cell rows centred on the indicated character centre row, and on one row above this, and on one row below this, in turn, this vertical jitter being provided as the character may not end exactly on row boundaries. Reference signals permanently wired in simulate an effective extension of the photo-cell array both in the determination of character top and bottom and at the inputs to the amplitude correlators, to eliminate edge effects.