| 摘要 |
PURPOSE:To enable to obtain an excellent binary signal even with an original without white part at the initial of scanning, by the sample hold of peak value immediately before a peak hold circuit which produces a threshold voltage to binarize a video signal is reset. CONSTITUTION:A video signal Sa read out and amplified A at an image sensor IS is held for the peak voltage at a peak hold circuit PH, and a voltage Pp is output to a sample hold circuit SH. The circuit PH is reset with a signal Pr from a timing pulse generator TPG within nonvideo signal period, but TPG feeds a signal Ps to the circuit SH immediately before the reset and the peak value held at the circuit PH is sample-held to output a voltage Ph. The threshold voltage dividing this voltage Ph by a resistor VR is given as the reference voltage Vs of a comparator COMP. COMP compares the signal Sa with the voltage Vs to output a binary signal. Thus, a suitable binary signal is obtained even to an original without white part at the beginning of scanning of the original. |
