| 摘要 |
Control circuitry for selectively controlling the contrast of a video picture displayed by a television receiver and for selectively controlling the color level of the video picture. The television receiver is of the type which has a controllable video amplifier for amplifying a luminance signal and a controllable chrominance amplifier for amplifying a chrominance signal. The control circuitry includes pulse generating circuits for generating contrast control pulses of selectively variable duty cycle and color level control pulses of selectively variable duty cycle.A contrast control circuit is responsive to the contrast control pulses for generating a contrast control signal in accordance with the duty cycle of the contrast control pulses. The produced contrast control signal is used to control the gain of the video amplifier so as to correspondingly control the contrast of the video picture. A color control circuit responsive to the color level control pulses generates a color level control signal in accordance with the duty cycle of the color level control pulses, and the color level control signal is changed proportionally with a change in the contrast control signal so as to maintain a substantially constant chrominance-to-luminance signal ratio despite changes in the contrast control signal. The color level control signal is used to control the gain of the chrominance amplifier so as to correspondingly control the color level of the video picture. In one embodiment, the duty cycles of the contrast control pulses and of the color level control pulses are remotely controlled, as by ultrasonic transmitting/receiving devices. |
