Patent GB-1445513-A (GB)
Title: Photographic image-pick-up and coding system of run-length type
IPC: H04N1/04
Filed: 1974-02-01
Abstract: 1445513 Copying by scanning MASTUSHITA ELECTRIC INDUSTRIAL CO Ltd 1 Feb 1974 [1 Feb 1973] 04775/74 Heading H4F Facsimile signals representing the black and white marks on a line of a medium 23 are derived by repeatedly scanning the line of the medium with a flying-spot scanner 20, the resulting signals from a photo-electric converter 26 being fed to circuitry 13 to produce, successively, at the output of a flip-flop 47, gate pulses of durations equal to the durations of the signals representing successive black and white marks on the medium 23, flip-flop 47 producing one gate pulse representing one mark during certain of the line scans of tube 20 and no output during other line scans; the gate pulses from flip-flop 47 are sampled by gate pulses in AND gate 60 and fed to a coder 17 which produces binary signals, each bit of which occupies one line scan period; coder 17 produces a coding completion signal one bit before the completion of coding of each mark and this causes flip-flop 47 to produce, during the next line scan period, a gate pulse representing the following mark; if successive line scans of flying-spot scanner 20 are displaced at right-angles to the direction of line-scanning, due, for example, to fluctuations in the power supply voltage, the gate pulse from flip-flop 47 during the second, displaced, line scan is in error and a correction circuit 70 is included to delete from the output signal of NAND gate 46, which signal resets flip-flop 47, the pulse, if any, which immediately follows the setting of flip-flop 47. The timing of the start of successive gate pulses from flip-flop 47 is controlled by binary counters 50, 51 and coincidence circuit 53, counter 50 counting the output pulses from AND gate 60 and thus storing the number of pulses representing the marks already coded in that line of medium 23, overflow of counter 50 indicating that the whole of that line has been coded and causing generator 15 to produce a vertical synchronizing pulse which clears counter 50 and moves medium 23 at right-angles to the direction of line scan; counter 51 is cleared by the coding completion signal from coder 17 and during the following line scan period counts the number of clock pulses from the beginning of that line, coincidence of the counts in counters 50 and 51 producing an output from coincidence circuit 53 which sets flip-flop 56 to produce from the output of inverter 59 a signal which sets flip-flop 47, enables NAND gate 46 for the remainder of that line scan period, and is fed to correction circuit 70. The facsimile signal from photo-electric converter 26 is passed via NAND gate 34 directly to a NAND gate 38 and via an inverter 36 to a NAND gate 37, clock pulses also being supplied to NAND gates 37 and 38. The outputs of NAND gates 37 and 38 are sampled signals representing respectively the black marks and the white marks. A flip-flop 43, which is triggered by the coding completion signal from coder 17, produces a "1" on the Q terminal and a "0" on the Q terminal when a black mark is to be coded and a "0" on the Q terminal and a "1" on the Q terminal when a white mark is to be coded. Thus only one of the AND gates 41, 42 is enabled at one time to pass a signal to NAND gate 46. The correction circuit 70 includes an AND gate (75, Fig. 7, not shown) whose output is connected to the reset terminal of flip-flop 47 and one of whose inputs is connected, via an inverter, to the output of NAND gate 46; the other input of the AND gate is connected via an inverter to the output of a monostable multivibrator which is triggered, via an inverter, by the output of inverter 59 and which produces a pulse of period slighly longer than the clock pulse period.