| 摘要 |
A document reading apparatus that includes a white platen roller and image sensor positioned at an image reading portion of the apparatus. The white platen roller is used to provide white reference data used for shading correction when reading an original document. The image sensor selectively reads the white platen roller and outputs signal characteristic data after reading the white platen roller. The apparatus also includes a controller configured to control the reading of the white platen roller so that the image sensor reads the white platen roller a predetermined number of times. The controller also controls movement of the white platen roller so that a motor used to move the white platen roller is de-energized when the image sensor reads the white platen roller. The controller receives the output signal characteristic data from the image sensor and compares the read output signal characteristic data to pre-existing signal characteristic data to determine if an abnormality exists in the read output signal characteristic data. When an abnormality is determined, the read output signal characteristic data is not used as white reference data but when no abnormality is determined the controller stores in memory the output signal characteristic data as white reference data.
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