a switching device to prevent the phenomenon of curvature in a television receiver and a means of preventing it.

摘要

Circuitry for preventing a doming phenomenon in a color television receiver includes circuitry (5, 6, 7, 8, 9, 10) for detecting the presence or absence of a high luminance portion not less than a predetermined area on a television receiver screen, and circuitry (11, 60, 2, 3) for slowly and gradually reducing at least one of luminance and contrast of the screen when the high luminance portion not less than a predetermined area exists on the screen. The area detecting circuitry includes a circuit (5, 6; 5 min , 6 min ) for detecting the presence of the high luminance portion on the screen, a first charge/discharge circuit 9 for generating a signal, the level of which shifts slowly in a first direction when this high luminance potion larger than a predetermined width exists, and shifts rapidly in a second direction when it is absent, a circuit (10) for comparing an output of the charge/discharge circuit with a second reference voltage and for deciding whether the area of the high luminance portion is not less than a predetermined area, a circuit (11) for generating a control signal for gradually reducing the luminance/contrast to the presence of the high luminance portion not less than a predetermined area in response to an output of the decision circuit and for rapidly recovering the luminance/contrast to the original state in response to the absence thereof.