| 摘要 |
PROBLEM TO BE SOLVED: To effectively utilize the photoelectric conversion range of a CCD for a scanner and to determine the gain of each of R, G and B required for taking gray balance. SOLUTION: The charge accumulation time of a CCD 4 is set up so that the CCD 4 is not saturated even when the light quantity of a lamp 1 is maximized and a CPU 6 controls an inverter control circuit 7 in the set state to change the light quantity of the lamp 1. Since the CCD 4 is sufficiently separated from a saturation range, the output level of the CCD 4 is linearly changed in accordance with a change in the light quantity. Since the output level of the CCD 4 obtained when the accumulation time is set up to the same time as normal scanning time can be expected, the light quantity can be found out by calculating an unsaturated level. A GCA 8 controls the gain on the basis of an output from a DA converter 10 and analog gain capable of unifying the balance of R, G and B signals is searched in each of R, G and B.
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