| 摘要 |
PURPOSE:To project a picture of an optimum contrast constantly to input video signals of different amplitudes and black levels by detecting the amplitude and the black level of the input video signal and making the amplitude and the black level of the video signal constant according to this detected signal. CONSTITUTION:The detected signals from a black level maximum value detecting circuit 31 and a black level average value detecting circuit 32 are supplied to a black level control signal forming circuit 33, the quantity of the dynamic change of the black level of the video signal is compared with the quantity of the static change to form a black level control signal suitable for the picture. Then, it is supplied to a black level control circuit 3 and the black level of the input video signal is automatically controlled. Thereby, the picture of the optimum contrast can be constantly projected to the input video signals of the different black levels and the amplitudes.
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