Synchronized demodulation of the chrominance signal with switched carrier phase angles

In a color video system of the type in which the chrominance component of a composite video signal is transmitted or recorded as a trisequential sequence containing the substitute color signals R', G', B' and in which at the receiving or playback end there is derived from the trisequential substitute color signals a luminance signal Y.sub.M = 0.33(R'+G'+B') where R', G', B' are chosen so as to substantially satisfy the relationship, Y.sub.M = +0.30R + 0.59G + 0.11B, required for black and white compatibility,

• the improvement that for producing said sequence of color signals there are provided:
• three phase demodulating means having a chrominance component input and also an input from a trisequential switch means said trisequential switch means being connected to phase-splitting means driven by a synchronized oscillator of color subcarrier frequency and supplying said trisequential switch with three color subcarrier phases .phi.1, .phi.2 and .phi.3 of such angles as to cause said demodulating means to trisequentially demodulate said chrominance component directly along the color difference axes R'--Y, G'--Y, B'--Y,
• gain control means interposed in series relationship with said demodulating means for automatically and trisequentially varying the chrominance component gain to bring about corresponding corrections of the magnitudes of the three individual color difference signals R'--Y.sub.L, G'--Y.sub.L, and B'--Y.sub.L, respectively, and
• a trisequential clock pulse generator connected to said trisequential means for synchronously driving said switch means and connected to said gain control means for synchronously correcting said magnitudes,
• whereby the need for means first producing the original colors R,G,B, and then processing the last mentioned colors to derive therefrom the substitute colors R',G',B', is obviated.

In a color video system of the type in which the chrominance component of a composite video signal is transmitted or recorded as a trisequential sequence containing the substitute color signals R', G', B' and in which at the receiving or playback end there is derived from the trisequential substitute color signals a luminance signal Y.sub.M = 0.33(R'+G'+B') where R', G', B' are chosen so as to substantially satisfy the relationship, Y.sub.M = +0.30R + 0.59G + 0.11B, required for black and white compatibility,

• the method of producing said sequence of substitute color signals, comprising the steps of:
• deriving from a synchronized unmodulated subcarrier three subcarrier phases along the axes R'--Y, G'--Y, B'--Y, respectively;
• synchronously demodulating the chrominance component of said composite video signal trisequentially along the associated axes with the aid of said subcarrier phases to generate the signals R'--Y.sub.L, G'--Y.sub.L, B'--Y.sub.L ;
• and adding thereto the luminance component Y=Y.sub.L +Y.sub.H of the composite video signal where Y.sub.L is the low-frequency portion and Y.sub.H the high-frequency portion of the luminance component, thereby to produce the trisequential signal (R', G', B') + Y.sub.H for transmission or recording.