| 摘要 |
PURPOSE:To optimize a reference level automatically by obtaining an average level of picture signals which is deviated to the white side from the distributing level at the midway of the white and black peak levels and by using the intermediate value of the average level and the black peak level as the reference level. CONSTITUTION:Picture signals (a) obtained through photoelectric conversion is give to an input IN and the white and black peak levels LWP and LBP are detected by a white peak detector WPD and a black peak detector BPD. Then, both peak levels LWP and LBP are divided in voltage by resistances R1 and R2 for voltage dividing, and a distributing level L1 at the midway of both peak levels LWP and LBP is obtained. Moreover, a picture signal average level L2 which is deviated to the white peak level side from the distributing level L1 is detected by an operational amplifier OP, etc. Thereafter, the intermediate value of the picture signal average level L2 and the black peak level LBP is inputted into a comparator CP1 as a reference level. |
