| 摘要 |
PURPOSE:To simplify a circuit constitution, to reduce cost, and to prevent an interference in a chrominance signal due to noises included in a luminance signal by inserting a carrier wave frequency trap for carrier chrominance signals in a luminance signal channel before the multiplexing of carrier chrominance signals, and controlling it to act when the illuminance of an object is lower than a prescribed value. CONSTITUTION:When the rays of light are made incident on a photodiode 71, an electric current is conducted to the direction of arrow, and the output of an amplifier 72 comes to a high potential. As the illuminance goes lower, the said potential goes lower. When the said lowering comes below the prescribed value, a transistor 73 turns ON to turn a switch transistor 61 ON, and the carrier wave trap 50 starts to operate. Consequently, the color carrier wave (f) frequency of the brightness signal and the frequency components in the vicinity of the said frequency among the noise components included in the luminance signal, are attenuated. And thus a noise interference in the carrier chrominance signal at the stage of multiplexing the signal is prevented from being occurred. When the illuminance is high, the traps 50 is in non- operating, to cause no attenuation of the higher components of the luminance signal. As a result, the high resolution can be maintained.
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