| 摘要 |
PURPOSE:To eliminate the need to adjust a threshold level by setting shading correction plates which correct the photodetection level on a line image sensor at the joint part of an image so that the level is maximum corresponding to the line image sensor. CONSTITUTION:The shading correction plates 12 and 12 arranged between a readout line RL and lenses 7 and 9 set distributions of photodetection levels of line image sensors 8 and 10 so that the quantity of light is maximum at the position corresponding to the intermediate position PC and its periphery. When the all-white part at DP is read, the output signal SV1 of the sensor 8 varies having a maximum value V1 at the intermediate position PC at the tail of a scan and the output signal SV2 of the sensor 10 varies having a maximum value V2 at the intermediate position PC at the head of the scan. Further, the photodetection distributions on the sensors 8 and 10 are maximum at the joint part of the image, so the maximum values V1 and V2 are almost at the same level. Consequently, the need to adjust the threshold level is eliminated.
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