| 摘要 |
An image reading apparatus includes a photoelectric transducer which reads an image of a document and outputs an analog image signal, an A/D converter which converts the analog signal to a digital image signal, and an offset level detecting circuit which determines an average value of output levels from picture elements in a predetermined range of the photoelectric transducer. Further, there is an offset setting unit which provides an offset in the analog image signal before the A/D conversion on the basis of the average value, a first comparing device which compares the average value to a predetermined target value, and an adjusting device which adjusts a size of the predetermined range of the photoelectric transducer on the basis of the result of the comparison.
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