US Patent 7633653 Image reading apparatus

An image reading apparatus includes a reading unit having contact glass through which an image is read from a document, backup glass located opposite the contact glass of the reading unit so as to form a conveying path between the backup glass and the contact glass through which the document is passed, a white member located on a rear surface side of the backup glass which is different from a contact glass side of the backup glass, a support plate that allows the white member to pivot between a position where the white member stands opposite the contact glass via the backup glass and a retract position where the white member is retracted from the position where the white member stands opposite the contact glass, and a regulating member provided between the backup glass and the white member so as to create a specified gap between the white member and the rear surface of the transparent member. Thus, a fixed distance is always maintained between the movable white member, located opposite the reading position, and the document reading surface. As a result, accurate shading correction data is acquired.