| 摘要 |
<p>PURPOSE:To prevent malfunction against a character or pattern having poor black-and-white contrast, by fixing a relative reference value when the difference between the signal of a present photodiode and that of a photodiode right or several units before changes between positive and negative repeatedly in a short time. CONSTITUTION:An analog subtracter 3 finds a difference between the output signal Esi of a photodiode element and the signal Esi-1 of a photodiode element right after outputted from a storage device 5, and then sends it to a controller 20A through a negative signal detector 4. The controller 20B sets a prescribed number in a counter 70 externally and also resets an FF50. Thus, the controller 20B is adjusted, and consequently while a counter 70 performs counting operation, a relative reference value Eref stored in a storage device 6 is not varied even if the output of a detector 4 becomes positive or zero immediately. Further, a comparator 17 finds (Eref-Esi)>=Eo (Eo; fixed reference value), a controller 20 fixes the Eref temporarily and maintains the state.</p> |
