Patent GB-1118571-A (GB)
Title: Method for improving sharpness of television images
Inventor: IZUMI HIROSHI
IPC: H04N5/92
Filed: 1967-01-03
Abstract: 1,118,571. Television. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 3 Jan., 1967, No. 293/67. Heading H4F. The invention relates to apparatus for improving the apparent resolution in pictures reproduced from television video signals which have been transmitted or stored by a system involving frequency modulation, e.g. crispening wide-band television signals which have been recorded upon a magnetic record member as a relatively narrow-band frequency-modulated signal. The apparatus comprises means for deriving from a carrier-wave frequency modulated with a video signal a first train of pulses representing successive transitions across a reference potential, e.g. zero, means for developing from the first pulse train a further pulse train each pulse of which represents the midpoint (or a selected intervening point) in the inter-pulse interval between successive pulses in the first train predicted on the assumption that in the first train each inter - pulse interval will be equal in duration to the preceding inter-pulse interval and means for adding the two pulse trains and for deriving from the resultant composite pulse train a signal varying in amplitude in accordance with the intervals between successive pulses therein, i.e. the demodulated video signal. In an embodiment of the apparatus a television signal having the waveform 5A, Fig. 5, is recording upon a magnetic tape 1, Fig. 4, as a frequency modulation of a carrier wave. The signal recovered from the tape by transducer head 2 is applied to a reproducing amplifier 3 and limiter 4 from which a limited signal as shown by waveform 5B is obtained. This signal is differentiated 5, waveform 5C, and amplified, waveform 5D. The train of unidirectional pulses thus derived is applied to a sawtooth generator 7, waveform 5E, the envelope of which connecting the apices of the successive sawtooth voltage pulses does not show the sharp rise and fall of the initial waveform 5A. The output of sawtooth generator 7 is applied to a triangular wave generator 8 which develops a voltage waveform 5F which alternately falls and rises with the same rate of change of voltage. The triangular waveform signal is differentiated 9, waveform 5G, and differentiated again 10, waveform 5H, and the positive going pulses waveform 5J only are selected from this waveform and amplified to form pulses of the same amplitude as those developed by pulse amplifier 6. These pulses, P n-1 , P n , P n +1  represent the times of the predicted mid-points between successive transitions in the recovered frequency modulated signal 5B, each pulse Px being delayed with respect to the preceding transition Zx by an interval equal to half the interval between the two preceding transitions, so that T n 1 = ¢T n-1 . Pulse trains 5D and 5J are mixed in pulse adder 11 to obtain composite pulse train 5K. This pulse train is applied to a sawtooth generator 12 to obtain a train of sawtooth pulses of constant slope and hence of peak amplitude proportional to the time-interval between successive pulses, waveform 5L. The resulting signal is fed through a low-pass filter 13 to yield a signal representing the envelope of the sawtooth waveform as shown by broken line R in waveform 5L, i.e. the demodulated television video signal. The Specification includes a detailed description of the circuits 5-11, Fig. 6, not shown.