| 摘要 |
PURPOSE:To improve a picture quality and to make the cycle of maintenance longer by reading a reference gradation picture using an image sensor before the start of the reading of an original picture and adjusting a reference potential at the time of the quantization of a picture signal of the original picture based upon the picture signal of the reference gradation picture. CONSTITUTION:A scanner 1 that uses an image sensor 12 is moved the direction of an arrow A in the reading time of the original and when it reaches to the end part of the original, it returns to a holding position shown in figure. In the holding position, it is constituted that a light beam from th outside is not as to be made incidence on the sensor 12 and a black picture is made incidence on the sensor 12. A control signal C1 is inputted to analogue switches (S) 21 and 25 which are made to conduct by the signal C1 in the holding position and the inverted signal of it is inputted to an S22. A digital value outputted from an AD converter 26 is stored at a register 29 by a control signal C2 that is outputted after the C1, and when the reading of the original is started, the converter 26 quantizes the picture signal of the original picture setting the offset value of the sensor 12 as the reference electric potential. Therefore, the picture quality is improved and the cycle of the maintenance is extended.
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