| 摘要 |
PROBLEM TO BE SOLVED: To obtain a video image with contrast by increasing a black detection level when a mean amplitude level of an input video signal is at a prescribed level or over so as to increase a black level part to be expanded thereby emphasizing the black level. SOLUTION: A black level detection circuit 6 sets a black detection level that is an operating point of black level expansion and gives a waveform of a back level that is the operating point or below to a gain control amplifier 7, which applies the black level expansion to the received signal. A video amplitude detection circuit 21 sums input video signals from an input terminal 1 for a prescribed time to obtain an average amplitude level, and gives a signal to the black level detection circuit 6 when the mean amplitude level is a predetermined level or over so as to set a higher black detection level to the circuit 6. Simultaneously a gain of the gain control amplifier 7 is controlled to expand the waveform with the black level below the operating point in a direction of the black level. Thus, the signal of the black level part is corrected to extend the depth of the black level direction and the time width.
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