| 摘要 |
PROBLEM TO BE SOLVED: To provide an image reading apparatus that properly corrects the black level of an analog image signal. SOLUTION: The image reading apparatus 1 is characterized in that when analog image signals Ve and Vo of a document read by converting reflected light from the document into an electric signal by a CCD image sensor 13 are converted into a digital signal by performing analog signal processing by a sample holding circuit 22, an amplifying circuit 25, a multiplexer circuit 24, and an amplifying circuit 25 after the analog image signals are AC-coupled by a capacitor 35, line-clamped by a black level correcting circuit 21, and adjusted to a designated clamp potential, and then comparing the image signals with a designated reference voltage by an A/D converting circuit 26, a black offset level detection section 27 detects the quantity of deviation of the analog image signals generated in the line clamping operation of the black level correcting circuit 21 from a reference clamp voltage and an A/D reference voltage generation section 28 adjusts the reference voltage of the A/D converting circuit 26 based upon the quantity of deviation. COPYRIGHT: (C)2006,JPO&NCIPI
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