1. Technical Field
The present disclosure relates generally to balance control, and more particularly, to a method and system for balance control, as opposed to tint control, for component video signals.
2. Background of the Related Art
Common practice when decoding NTSC signals is for a “tint” or “hue” adjustment to compensate for possible differential phase errors between a QAM chroma signal and its accompanying burst reference. Tint adjustment is also useful in compensating for other possible system errors.
Additionally, tint adjustment together with saturation adjustment allows for variations in personal preference to be accommodated, permitting any color to be shifted in saturation and hue without affecting the gray scale. In order to retain this capability for video signals that do not experience NTSC decoding, such as component video signals, e.g., from a DVD player or set-top box, it is generally necessary to apply tint adjustment to the baseband color difference signals.
The three main component video signals as known in the art are Y, B−Y and R−Y. Derived from the Y, B−Y and R−Y component video signals, Y/U/V and Y/Pb/Pr are defined as follows: U=(B−Y)/2.03, V=(R−Y)/1.14, Pb=(B−Y)/1.772 and Pr=(R−Y)/1.402. U and V amplitude scaling is applied in encoding an NTSC signal to prevent RF overmodulation as known in the art. Pb and Pr amplitude scaling is applied to parallel component video signals to make each signal approximately equal to 0.7 Volt p-p.
Prior art tint control circuitry, as shown by FIG. 1, derive the bi-directional crosstalk components, i.e., +/−kU for coupling into V and −/+kV for coupling into U, necessary for tint control. The opposite polarities associated with the bi-directional crosstalk components are significant, since they are equivalent to the effect of a tint control in NTSC decoding which is derived as follows:
As known in the art, an NTSC chroma signal may be represented as follows: C(t)=[V cos ωt+U sin ωt], ω=2πfsc. Therefore, demodulating V and U with 2 cos(ωt±φ) and 2 sin(ωt±φ), respectively, and tint range being ±φ, the bi-directional crosstalk components can be derived.Vdemodulation=[V cos(ωt)+U sin(ωt)]2 cos(ωt±φ)=2V cos(ωτ)cos(ωt±φ)+2U sin(ωt)cos(ωt±φ)=V[cos(2ωt±φ)+cos(±φ)]+U[sin(2ωt±φ)−sin(ωφ)]=V cos(±φ)−U sin(ωφ), disregarding 2ωt terms=V−U sin(ωφ), for small values of φ=V−kU, k=sin φUdemodulation=[V cos(ωt)+U sin(ωt)]2 sin(ωt±φ)=2V cos(ωτ)sin(ωt±φ)+2U sin(ωt)sin(ωt±φ)=V[sin(2ωt±φ)+sin(±φ)]−U[cos(2ωt±φ)−cos(±φ)]=U cos(±φ)+V sin(±φ), disregarding 2ωt terms=U+V sin(±φ), for small values of φ=U+kV, k=sin φ
As evident from FIG. 1, prior art tint control circuitry for consumer electronics devices, such as high definition monitors and other imaging devices and appliances, in order to obtain the bi-directional crosstalk components +/−kU and +/−kV is generally complex. Further, the prior art tint control circuitry as shown by FIG. 1 employs two modulator/demodulator ICs, i.e., the MC1496 balanced modulator/demodulator ICs which contains eight transistors, and peripheral circuitry, which add to the cost of the high definition monitors and other imaging devices and appliances. Further still, the prior art tint control circuitry as shown by FIG. 1 and most other prior art tint control circuits introduce a variable amount of bi-directional, opposite polarity crosstalk between the component video channels.
A need therefore exists for an alternative method and system which provide a less complex and lower cost approach for adjusting or compensating for possible color encoding errors, as well as allowing individual viewer preferences to be accommodated. A method and system are also needed which do not introduce a variable amount of bi-directional, opposite polarity crosstalk between the component video channels.