| 摘要 |
An image reading apparatus comprises a correction coefficient determining circuit 4 for determining a correction coefficient per each bit of white reference data in a main scanning direction which are read immediately before reading an original image, a correction coefficient modifying circuit 5 for producing a modified correction coefficient, and a correction coefficient predicting circuit 6 for producing a predicted correction coefficient with reference to the modified correction coefficient. If an absolute value of a difference between the correction coefficient and the predicted correction coefficient is smaller than and not smaller than a predetermined threshold value, the correction coefficient modifying circuit 5 produces the correction coefficient and the predicted correction coefficient as the modified correction coefficient respectively. A correction coefficient memorizing circuit 7 memorizes the modified correction coefficient as shading correction coefficient data. The correction coefficient predicting circuit 6 produces the predicted correction coefficient for a particular bit of the white reference data in the main scanning direction with reference to at least a preceding adjacent bit preceding the particular bit in the main scanning direction.
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