Contrast/brightness control circuit for television receiver

DETAILED DESCRIPTION It is, therefore, an object of the present invention to provide a television receiver which overcomes the problem of the conventional television receiver.
Another object of the present invention is to provide a television receiver is able to prevent the contrast and the brightness from worsening lower than it required on the displayed picture of the picture signal which is less varied the average picture level when at least one of average picture levels of the plurality of picture signal varied at a rate different from the others.
In order to achieve the above object, a television receiver according to one aspect of the present invention is subjected to the one which is capable of simultaneously displaying a picture signal by at least first end second picture images on a cathode ray tube, and including means for generating the first and second picture signal, a superimposer for selectively supplying the first and second picture signal to the cathode ray tube, an APL detector for receiving the first end second picture signals to detect respective average picture levels of the first end second picture signals respectively thus producing first and second level detection signals, an ABL detector for generating a detection voltage responsive to a variation in an anode current of the cathode ray tube, and control means for controlling at least one of contrasts and brightnesses of the first and second picture signals by commonly operating on the first and second picture signals in response to the first and second detection signals from the ABL detector, as well as for independently controlling at least one of contrasts end brightnesses of the first and second picture signals in response to the first and second detection signals from the APL detector.
According to the television receiver having such an arrangement, the control means operates in common on the first and the second picture signals in response to the detection voltage from the ABL detector.
Then the control means not only controls at least one of contrasts and brightnesses of the first and the second picture signals, but also independently controls at least one of the contrasts and the brightnesses of the first and the second picture signals in response to the first and the second detection signals from the APL detector