| 摘要 |
PURPOSE:To effectively use the dynamic range of a picture signal processing circuit by correcting the output level of respective color picture signals outputted from an image sensor to the prescribed reference level at the time of reading the black picture of an original. CONSTITUTION:When a CCD chip reds the black part of an original, the output signal of white balance correcting part 140 is corrected by a black level correcting part 150 so that the black level of respective colors and the black level between respective CCD chips can be the minimum level of an A/D converter 161, respective original color signals of the black level corrected B, G and R are further amplified to the dynamic range of the A/D converter 161 by a buffer amplifier 160 and continuously, converted to the digital value by the A/D converter 161. Then, the reference electric potential of a reference electric potential generating circuit 153 is set beforehand so that the black level of the black color can be coincident to the minimum reference level of the A/D converter 161 when the black color of the original is read, and the black level is corrected and the clamping of the output signal is simultaneously executed.
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