| 摘要 |
PURPOSE:To reproduce always a stable black level by providing a comparator circuit for the set black level and the black level of a video signal and resetting the set black level according to the result of comparison so as to absorb the fluctuation of the black level due to the fluctuation of a set up level. CONSTITUTION:An operation circuit 4 makes the black level of the output digital video signal 10 coincident with the setting black level given by a signal 13 independently of the black level of the video signal is input. The comparator circuit 5 compares the video signal subject to pedestal clamp with the setting black level signal 13 outputted from a level adjusting circuit 8 and when the minimum level (black level) of the video signal is smaller than the level of the setting black level signal 13, a detection signal 14 is outputted. A counter circuit 6 counts the number of generation of the detection signals 14 and when the count reaches a prescribed count number with a prescribed time, a count- down signal 15 is outputted. When the prescribed count number is small, the sensitivity of black level detection is increased, and when larger, the sensitivity is lower.
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