| 摘要 |
<p>PURPOSE:To enlarge the contrast of a recording image while matching with an image by detecting the voltage of the minimum level of an RGB video signal in an effective picture with a minimum level setting means and adding a voltage, which corresponds to the output of this detecting means to the negative reference of an A/D converter. CONSTITUTION:An analog switch 24 is turned on only during the effective picture by a signal (c) to express the effective picture. This electric potential is held by a capacitor 25 and impedance-converted by a transistor 26. Then, a voltage shift part by diodes 20, 21 and 22 is compensated and the potential goes to be a minimum level detecting output (j). When the minimum level detecting output (j) is higher than a prescribed voltage (m), a transistor 30 is cut-off. By resistances 40 and 41, a black level setting means receives the potential, which executes the interior division of a black level limiting means output l and a pedestal potential (h), by a buffer with an operating amplifier 42 and outputs it as a black level setting output. By changing the ratio of the resistances 40 and 41, the degree of the emphasis of the contrast is controlled and an over-contrast can be controlled.</p> |
