| 摘要 |
A reference light from a reference reflective surface is projected onto an image sensor to form an output signal from the image sensor corresponding to the distribution of a reference light. This output signal is stored in a memory as a reference signal used for shading correction. An output signal from the image sensor corresponding to a document image is corrected in accordance with the reference signal. Irrespectively of whether or not the document is being read, the image sensor is irradiated by the reference light at a predetermined point of time to renew the reference signal.
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