| 摘要 |
PROBLEM TO BE SOLVED: To provide an image reader provided with a low-cost means capable of outputting a digital image signal maintaining a wide dynamic range without employing a conventional system in which gain adjustment of a variable gain is wholly used. SOLUTION: A CPU 29 sets one main scanning time of a length capable of obtaining a CCD output of an S/N corresponding to a color or monochrome mode selected by an operation unit 38 in a driving circuit 21 of a CCD 9, and changes a preset value of a reference voltage in an A/D conversion circuit 26 so as to correspond to the output mode in order to maintain the wide dynamic range even depending on a change in CCD output generated by a change in output mode. Since the preset value of the reference voltage is changed in proportion to the one main scanning time, a means can be simplified. COPYRIGHT: (C)2004,JPO
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