| 摘要 |
PURPOSE:To prevent deterioration of picture quality by amplifying a difference of peak values of white/black information level read by a read sensor array and bringing the voltage to a prescribed voltage or over. CONSTITUTION:In lighting an LED array 7, the light is reflected from a white roller 6 and its reflected light is led to a read sensor array 14 through a condenser lens 3 as white background information. Then a switch SW5 is turned on, a switch SW7 is turned off and this level is stored in a capacitor C1 of a peak value detecting circuit 20 to represent a peak value VP1. In extinguishing the array 7, a black background information peak value VP2 from the capacitor CP2 of the circuit 20 is obtained. The VP1, VP2 are amplified differentially, an output VP3 is compared with a reference voltage VREF by a comparator 22 and when VP3>VREF, the output VP4 goes to a low level and no gradation of the picture is caused. On the other hand, in case of VP3<VREF, the VP4 goes to a high potential, an output of a pulse generating circuit 24 is given to an AND circuit 23, its output is increased more than the VREF to actuate stably a shift register 18.
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