| 摘要 |
PURPOSE:To enable to obtain excellent binary signal, even if no white part is present at the initial part of an original, by automatically setting a threshold voltage to a given voltage value if the threshold voltage to binarize a video signal is less than the specified value. CONSTITUTION:A video signal Sa read out from an image sensor IS is amplified A and the peak voltage of the video signal is held at a peak hold circuit PH, and a voltage Vs divided with a resistor VR is given to a comparator COMP as a reference voltage and it is compared with the signal Sa to obtain a binary signal of white and black level. If the voltage Vs is lower than the predetermined voltage value, a voltage Vf set at a minimum threshold set circuit LS is given to COMP as the reference voltage. Accordingly, even if no white part is present to a original corresponding to the initial part of the video signal read out from IS, an excellent binary signal is obtained. |
