| 摘要 |
PURPOSE:To obtain a binarization signal giving the reproducibility of a prescribed picture at all times even when an instable light source such as a fluorescent light is used by sampling and holding a white level obtained by reading a white level reference detecting means by means of a line image sensor. CONSTITUTION:White level reference detection means AS1, C1, OP1 provided in a picture frame in a direction orthogonal to the line direction of a line image sensor, white sampling circuits AS2, C2 and OP2 sampling and holding the white level voltage of an analog video signal VDO, means R3, C3, OP3 forming a threshold level and a comparator CP comparing the analog video signal VDO with a threshold level and outputting the binarization signal B of the analog video signal are provided. Then the white level voltage obtained by reading the white level reference detected means provided in the picture frame is subjected to sample holding. Thus, the binarization signal B giving always constant picture reproducibility is obtained regardless of the fluctuation of the luminous quantity of an original lighting source.
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