Image Reading Device, An Image Forming Apparatus, and Methods for Detecting Dirt in Document Reading Positions

摘要

An image reading device includes a changed-pixel detection unit and a determination unit. The changed-pixel detection unit detects, from image data read by the image reading unit, a changed pixel having a pixel value that differs from that of an adjacent pixel in the main scanning direction. The pixel value may differ by more than a predetermined value. The changed-pixel detection unit detects the position of the changed pixel in the main scanning direction. The determination unit determines that image data corresponding to positions of the changed pixel for the image data obtained by reading the document corresponds to a foreign image. The positions are consecutive in the sub-scanning direction. The positions of the changed pixel are detected for the image data obtained by reading the document and the image data obtained by reading the white guide member.