| 摘要 |
PURPOSE:To improve the S/N of a video signal deteriorated due to the decrease of the quantity of light in photographing by varying the quantity of noise cancel by a variable attenuator in which the frequency characteristic of the quantity of attenuation is controlled in accordance with the quantity of light in an image picking-up of an input video signal. CONSTITUTION:The video signal Y is supplied from an input terminal 10A to a delay circuit 11 and the first and the second signal subtractors 12, 15. A limiter 13 forms a noise cancel signal only by a noise component. The variable attenuator 14 controls the signal level of the noise cancel signal and changes the quantity of the noise cancel. Namely, by the detecting output of the signal level according to the quantity of light in the image picking-up supplied from a detecting circuit 7 to a control input terminal 10B, the frequency characteristic of the quantity of attenuation is controlled. The attenuator 14 has a switching transistor and is switching controlled by the detecting output from the detecting circuit 7. The attenuator 14 is turned on by the detecting output of the video signal to an object of a prescribed quantity of light in the image picking-up and turned off by the detecting output of the video signal of the object below the prescribed quantity of light in the image picking-up.
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