| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to normalize the optical black level of a CCD image pickup element without being followed by line flickers and to reduce the circuit scale and power consumption. SOLUTION: An optical black part being outputted from a CCD image pickup element 1 is extracted and a clamp level in each line is obtained by an integrating and averaging circuit 6. A comparator 10 calculates a difference between the clamp levels of adjacent lines and its absolute value. A selector 16 selects the clamp level of each line and a clamp level updated by +1 or -1 in accordance with a discriminated result whether the absolute value of the difference between the clamp levels of the adjacent lines is included within a prescribed range or not. The clamp level outputted from the selector 16 is subtracted from the output of the element 1. Consequently generation of line flickers can be suppressed even when the clamp level of each line is used.
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