| 摘要 |
PURPOSE:To improve gradation characteristics by comparing the mean value of luminance signals from an image pickup means with a peak value, modulating a prescribed iris setting input on the basis of the compared output and controlling the mean value of the luminance signals by using the modulated signal as a reference signal. CONSTITUTION:A luminance signal 11 is inputted to a mean value detecting circuit 1, the means value is detected and the detected means value is outputted as a luminance mean value 16. On the other hand, the signal 11 inputted to a peak detecting circuit 4 is peak-detected and outputted as a luminance peak value 18. The mean value 16 is amplified 5 twice and outputted as an amplified mean value signal 17, the peak value 18 is modulating signal is outputted. An iris setting input 20 is inputted to an iris modulator 7 and modulated on the basis of the signal 19. On the other hand, and input sets up a white level to a prescribed reference level when the periods of white and black levels are equal to each other, and when the signal 19 is positive or negative, outputs an iris correcting signal 21 for reducing or increasing the prescribed white level value. The means value 16 is compared with the signal 21 by an iris control circuit 2 and an output signal 22 from the circuit 2 is converted and amplified into a signal capable of driving the iris device by an iris driving circuit 3.
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