Patent ID: 8810823

Claim:
An image reading device comprising: an image reading unit that optically reads, on a line-by-line basis, a document at a predetermined document reading position through a document glass, wherein each line extends in a main scanning direction; a white guide member disposed at the document reading position so as to face the document glass, wherein the white guide member is read by the image reading unit; a document conveying unit that conveys the document toward the document reading position, wherein the document conveying unit directs the document to travel between the white guide member and the document glass; a changed-pixel detection unit that, based on image data read by the image reading unit, is configured to detect: (a) a changed pixel with a pixel value that differs from a pixel value of an adjacent pixel in the main scanning direction by more than a predetermined value, and (b) a position of the changed pixel in the main scanning direction; a reference member read by the image reading unit to obtain reference image data for shading correction; an image processing unit that performs the shading correction on the image data obtained by reading the document using the image reading unit; a determination unit that determines, after the shading correction, based on the position of the changed pixel in the main scanning direction, whether or not: positions in the main scanning direction of the changed pixel of a first line of the image data obtained by reading the document conveyed by the document conveying unit are the same as positions in the main scanning direction of the changed pixel of a last line of the image data obtained by reading the white guide member immediately before or after reading the document, and/or positions in the main scanning direction of the changed pixel of a last line of the image data obtained by reading the document conveyed by the document conveying unit are the same as positions in the main scanning direction of the changed pixel of a first line of the image data obtained by reading the white guide member immediately after reading the document, wherein when the determination unit determines that the positions of the changed pixel are consecutive in the sub-scanning direction, the determination unit determines that the positions of the changed pixel for the image data obtained by reading the document correspond to a foreign image, and wherein the positions of the changed pixel are determined from the image data obtained by reading the document and the image data obtained by reading the white guide member.