| 摘要 |
PURPOSE:To improve the S/N of R, G, and B primary color signals of double density by compensating the black level after conversion to R, G, and B primary color signals of double density. CONSTITUTION:A minimum luminance signal is taken out from the Y signal of double density by a detecting circuit 9, and a pedestal level is taken out by a pedestal level detecting circuit 10. The difference between the minimum luminance signal level and the pedestal level is taken out by a differential circuit 11, and a switch is so operated that R, G, and B primary color signals of double density are added only in the period of the pedestal level, and the pedestal level of R, G, and B primary color signals of double density is varied in an adding circuit 12 by the minimum luminance signal level and is allowed to pass a pedestal clamping circuit 13 to compensate the black level by the minimum luminance signal level. Since levels of signal components of R, G, and B primary color signals inputted to an A/D converter 5 are not changed by black level compensation, the dynamic range of the A/D converter 5 is used up to the maximum to improve the S/N.
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