| 摘要 |
PURPOSE:To obtain stable images even when an exposure lamp is used at the commer cial frequency and to obtain constant-level image signals for originals having the same density by providing a delay circuit, a D/A converter, an adder, etc. CONSTITUTION:When an original is read, a standard pattern 30 having constant density is lighted as an original 6 by an exposure lamp 2 and then an analog signal correspond ing to the reflection density is outputted from an image pickup element 20 and written in a RAM 50 through an A/D converter 44, etc. The AC component of the output of a light quantity sensor 32 which detects the quantity of light of the exposure source is synchronized with the reference voltage of a converter 44 through a delay circuit 34 and added at a specific ratio by an adding circuit 36, so that the sum is used as the reference voltage of the converter 44. Then, this reference voltage is used to con vert the output voltage during next output operation from analog to digital and the quantity of light is adjusted until contents written in the RAM 50 attains to a specific value. Thus, the output of the image pickup element 20 which uses the exposure lamp 2 turned on at the commercial frequency is corrected with the signal obtained by delaying the output of the light quantity sensor 32 to stabilize an image signal.
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