| 摘要 |
PURPOSE:To improve the precision of reading operation without reference to the kind of an original by selecting a readout threshold level, generated by dividing a maximum and a minimum voltage obtained by detecting a white and a black image, according to the nature of the original. CONSTITUTION:A maximum and a minimum voltage held in holding circuits 11 and 13 by detecting a white and a black image on an original are divided through resistances R1 and R2, and R3 and R4 to generate threshold voltages VT1 and VT2. In this case, the VT1 is set to 70-80%, and the VT2 to 20-30% of the maximum voltage. Then, the VT1 for a white-ground original or the VT2 for a black-ground original is inputted to a binary discriminating circuit 12 by changeover a switch 14 to discriminate the black and white of the image from a signal line 4. Consequently, reading operation free of omission of information is performed without reference to the kind of the original. |
