Patent GB-1021092-A (GB)
Title: Improvements relating to colour television receivers
Inventor: KARWOWSKI WIESLAW ANTONI
IPC: H04N11/14
Filed: 1961-03-02
Abstract: 1,021,092. Colour television receivers. ELECTRIC & MUSICAL INDUSTRIES Ltd. May 1, 1962 [March 2, 1961], No. 7469/61. Heading H4F. The invention relates to a colour television receiver utilizing a single gun sequential display tube adapted for the reception of a waveform in which the conventional gamma corrected 1/ γ  1/ γ  luminance signal Ey<SP>1</SP>= 0À59 EG + 0À30 ER <SP>1</SP>/γ +0À11 E B  is replaced by a luminance signal <SP>1</SP>/ γ  <SP>1</SP>/ γ  Ey = (0À59 E G  + 0À30 E R  + 0À1 E B ) . The received signal also comprises a first colour 1/ γ  1/ γ  difference signal E R  - Ey , a second 1/ γ  1/ γ  colour difference signal E B  - E Y  modulated in phase quadrature on a sub-carrier wave. When the red, blue and green signals are derived by linear matrixing the red and blue signals are of correct amplitude but the green signal has an 1/ γ  error term given by 1À7 (Ey - Ey<SP>1</SP>). It is the object of the invention to reduce the effect of this error. Embodiments are described utilizing the reversing colour sequence, i.e. R. G. B. G &c., but adaptable by suitable gating to a continuous colour sequence R, G, B, R &c. In one arrangement, Fig. 3, derived colour component signals are applied to the gun of the tube 1 in the sequence red, green, blue, green &c. by means of the gates 5, 6, 7 controlled by pulse generators 8, 9, 10, respectively. The gate 7 is further controlled by the harmonic generator 12 to open twice as often as the gates 5 and 6 since the system operates in a reversing colour sequence. To compensate for the error term in the green signal the time for which the gate 7 is opened is controlled by a signal applied to generator 10 to width modulate the pulses, the operation being such that the period for which gate 7 is open is reduced with increasing saturation of reproduced colour. The signal is derived from a divider circuit, not shown in the present Specification but which may be arranged like divider 209 in Fig. 7 of Specification 1,008,512. The divider functions to divide the colour modulated sub-carrier wave by the luminance signal to give a resultant signal which is representative of saturation per unit of luminance. In a second similar arrangement, Fig. 4 (not shown), utilizing colour difference signals, the red difference signal is controlled by the harmonic generator and the pulse width control signal (that is the saturation signal) is applied to the green difference signal gate. A third embodiment, Fig. 6 (not shown), uses beam gating and is based on the display systems described in Proc. I.R.E. Vol. 42, No. 1, Jan. 54, pp. 299- 308. The correction for the given signal is effected by additionally modulating the cathoderay tube beam by an oscillation the amplitude of which is controlled in accordance with saturation and the phase of which is such that the negative peaks coincide with the application of the green signals to the tube. The frequency of the oscillation is equal to the colour subcarrier frequency for systems operating with the continuous colour sequence and the second harmonic thereof for systems operating with the reversing colour sequence.