System for compensating for the violation of the constant luminance principle in color television systems

Claim 1

In a color television system in which picture information is carried by means of a luminance signal and color difference signals and in which the luminance signal is generated by matrixing predetermined portions of full bandwidth gamma corrected first, second and third color signals, apparatus for compensating for the violation of the constant luminance principle that normally occurs when said luminance signal is generated with conventional matrices, said apparatus comprising: compensation signal generating means having a plurality of inputs and a compensation signal output, for generating a compensation signal at said output in response to signals applied to said plurality of inputs; means for applying signals containing only the frequencies of at least one of said first, second and third color signals higher than a selected crossover frequency of the frequency band of said color difference signals, each attenuated by a predetermined amount, to a respective input of said generating means, means including means for matrixing said first, second and third color signals to produce a luminance signal and for applying the high frequencies of said luminance signal to a fourth input of said generating means; said compensation signal generating means including selecting means for producing at its output a signal that corresponds at any given time to the highest positive-going transition and the highest negative-going transition of the applied signals when all input signal transitions have the same polarity and for producing at its output, when all input signal transitions do not have the same polarity, a signal equal to a linear combination of the highest positive or negative-going transitions of a given polarity and the highest positive- or negative-going transitions of signals having a polarity opposite from said given polarity; and means for combining said compensation signal with the high frequencies of said luminance signal and producing a compensated high frequency luminance output signal, said combining means including selection means for producing, when the high frequency luminance transitions have the same polarity as the transitions of said compensation signal, an output signal which at any given time consists of the highest positive-going transition of said high frequency luminance signal or of said compensation signal and the highest negative-going transition of said high frequency luminance signal or of said compensation signal, and for producing, when the high frequency luminance transitions do not have the same polarity as the transitions of said compensation signal, an output signal which at any time consists of the algebraic sum of the opposed polarity high frequency luminance transitions and the compensation signal transitions.