| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to normally perform light quantity fluctuation correction even though stain is stuck to a reference reflection member. SOLUTION: When image data are fetched, data for one line from the image data are stored in a line memory (step S52), and the peak value (a peak value of reflected light from a position corresponding to the part of the reference reflection member provided in a vertical scanning direction) of a peak detection gate period set by a set holding part is simultaneously held in a peak value detection circuit (step S53). When the lowest peak value preliminarily set in the set holding part is compared with the peak value read from the reflected light (step S54) and the peak value read from the reflected light is lower than the lowest peak value, the peak detection gate period is changed to another period to be set by automatically switching set patterns of the peak detection gate period again (step S56), and the processing is returned to the step S52 to read a peak value from the reflected light.
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