JPS56105581A - Slice level generating system - Google Patents

Abstract

PURPOSE:To obtain an accurate video shaping signal by storing white level voltages respectively independently for the respective sensor cells of a sensor circuit thereby decreasing the effect of the variance in sensitivity or the variance in illumination of an optical system owing to the positions of sensors. CONSTITUTION:When the cells of a sensor circuit 12 scan the place of a medium 302 where there are no marks, a video signal 113 is outputted from an amplifier circuit 13, and enter as input to a comparator 19 and a voltage follower circuit 14. Here, the voltage follower circuits 14, 15 compare the video signal 113 and the signal 116 from a voltage dividing circuit 17 and output the either of the signals having a higher voltage as a white level signal 114. When the power source is turnd on, all the storage contents of an analog register 16 are 0V, hence the output signal 115 of the register 16 and the output signal 116 of the circuit 17 are both 0V and therefore while the sensor circuit 12 is making scanning, the video signal 113 is straightly the white level signal, which is stored in the register 16 in synchronization with the clock signal 111. The video shaping circuit 118 which is the output of the output of the comparator 19 maintains ''0''.