| 摘要 |
PURPOSE:To reduce the size of a device and to expand a read range by using a conveying means composed of a white member instead of a white reference plate. CONSTITUTION:A feed roller 6 is composed of the white member instead of the white reference plate, the brightness on the surface of the feed roller 6 is read before an original reaches a readout position, and its peak value is stored by a peak value detecting circuit 9. This peak value is voltage-divided by a resistance voltage divider 10 to generate a judgement level (absolute black level detection level) 25 of black, which is inputted to the uninverted input terminal of a comparator 11. The peak value of the brightness on the surface of the original sent to the readout position, on the other hand, is stored by another peak value detecting circuit 8. This peak value is inputted to the comparator 11 and compared with the black judgement level. The comparator 11 outputs '1' when the input level +IN is larger than the input level -IN.
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