Patent GB-1328569-A (GB)
Title: Colour image display apparatus
IPC: H04N9/43
Filed: 1970-09-15
Abstract: 1328569 Television PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 15 Sept 1970 [18 Sept 1969] 44021/70 Heading H4F A monochrome video signal is displayed in different colours in dependence upon its amplitude by phase modulating a carrier and either phase demodulating the resulting phase modulated carrier at different phases to provide effective colour signals which are applied to modulate the three beams of a colour television display tube, or applying the phase modulated carrier to a beam-indexing type display tube, in both cases the video signal being also coupled to the display tube in such a manner as to bypass the phase modulator. In a first embodiment the synchronizing signals and luminance component of a video signal from a pickup 1 are selected by amplitude selective circuits 11 and 7. The luminance component is fed via a control amplifier 25 which maintains the black level and the difference between the black level and the white level constant and via gamma correction circuits 59 and 31 and a D.C. level correction circuit 38 to a phase modulator 65 and a matrix 41. Matrix 41 supplies R, G and B or Y, R-Y, G-Y and B-Y signals to the display CRT 21. A carrier signal from an oscillator 71 is applied to modulator 65 and the modulated output is, if necessary, frequency tripled 77, filtered 83 and amplitude limited 89, and applied to synchronous detectors 95 and 99 to which is applied reference signals preferably 90 degrees out of phase (phase shifting network 127) derived from the oscillator 71 via phase-adjusting circuit 109 frequency tripler 115 and filter 121. Phase shifting network 127 may alternatively be included between limiter 89 and detector 95 or detector 99. The colour displayed for a given signal amplitude may be varied by phaseadjusting circuit 109, the amount of colour variation for a given amplitude variation being determined by gamma correction circuit 59. The colour display may alternatively be modified by including adjustable amplifiers between the demodulators 95 and 99 and the matrix 41. Reverse colour dependence on amplitude may be obtained by reversing the polarity of the video signal applied to modulator 65. An amplitude modulator may be included in one or more of the four input paths to demodulators 95 and 99, the luminance signal (possibly gamma corrected) being fed thereto. Phase adjusting circuit 109 may alternatively be included between the oscillator 71 and the modulator 65. A third synchronous demodulator, e.g. for G-Y, may be provided. The frequency tripler circuits 77 and 115 may be omitted if the phase modulator gives a modulation depth of 360 degrees instead of only 120 degrees. In a second embodiment an indexing-type display tube is employed the oscillator 71 being replaced by a circuit coupled with the indexing signal output thereof, and the detectors 95 and 99 being omitted, the phase-modulated signal from modulator 65 being applied directly to the display tube after being brought to the correct frequency. The reference signal circuit from oscillator 71 is omitted. The pick-up apparatus 1 may comprise an X-ray or gamma ray pick-up apparatus, a flying-spot scanner, or thermographic apparatus for obtaining a temperature image. Reference has been directed by the Comptroller to Specification 1,294,584.