| 摘要 |
PROBLEM TO BE SOLVED: To reduce a quantization error due to shading correction by controlling a dynamic range at the time of input to an A/D converter to become large as much as possible in the main scanning reading area of an original. SOLUTION: The bright time peak detection circuit 17 of a main scanning reading area is installed. The main scanning reading area is designated by a CPU 15. The CPU 15 decides an analog gain on a bright time peak value obtained in the main scanning reading area and the reference of shading correction on a bright time peak position where the bright time peak value is obtained is installed. In the device, the bright time peak detection circuit 17 searches a bright time peak point in the main scanning area of the original when a reading instruction is received. The CPU 15 sets the analog gain with which the dyadic range in input to the A/D converter 12 at the bright time peak point comes close to a maximum. A shading correction circuit 13 executes shading correction based on the bright time peak point as the reference.
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