| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the need of a high-resolution D/A conversion circuit, to avoid an image density step, and to reduce costs, by correcting the black offset level of a read image signal into a target value. SOLUTION: A document is read by converting reflection light from the document into an electric signal by a CCD 19, analog signal processing is performed for the read image signal by a clamp circuit 2021, a sample-hold circuit 2022 and a VGA 2023, and an analog image signal is converted into a digital image signal by an ADC 2024. On a front stage of the ADC 2024, an analog offset voltage from a first DAC 2027a is added, and on a back stage of the ADC 2024, a digital offset amount corresponding to or lower than the analog offset voltage, which is applied on the front stage, is subtracted by a 0-level control section 2027b. Then, a digital offset correction section 2025 performs correction, on digital output from the ADC 2024, for obtaining a desired black offset level. COPYRIGHT: (C)2011,JPO&INPIT
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