JPS5685989A - Automatic color balance adjusting circuit - Google Patents

Abstract

PURPOSE:To obtain a color balance with high accuracy at all times against a variation of color temperature of the illumination light source, by automatically adjusting the white balance and the black balance whenever a white object is photographed. CONSTITUTION:An object to be photographed, containing a white part is photographed by a color TV camera, and when the high level of its each channel video signal exceeds the detected level of the G, R, and B white signal detection circuits 21a-21c, the high level is output to its output. The NAND gate circuit 22 is operated by its output, the G, R an B signal gate circuits 23a-23c are gated, the outpt of said each circuit is converted to DC voltage, and it is provided t the R/G and B/G comparators 25b, 25c. And, when the levels of the R, G and B signals are different, the control voltage is applied to the R and B gain control circuits 6b, 6c from the circuits 25b, 25c, the outputs of the circuits 25b, 25c are adjusted so that they become zero potential, and the white balance adjustment is executed. In case of the black balance adjustment, too, it is executed in the same way by automatic adjustment of the R and B pedestal control circuits 3b, 3c.