Image reading apparatus for optically reading the contents of a conveyed

Abstract

An image reading apparatus in which a document conveying roller is provided on one surface side of a transparent member provided on a document conveying path and at least one light source is provided on the other surface side of the transparent member to direct light to the document through the transparent member while being conveyed along the transparent member and light-receiving elements receive light, which is reflected from the document, so as to read out document information. In the image reading apparatus, in order to eliminate a variation in the detection output of the reflected light resulting from a variation in the detection characteristic of the light-receiving element, the roller for document conveyance is white and the light reflected from a roller area is detected by the light-receiving elements to obtain a signal as a reference white level signal. A plurality of unenlarged white sections are provided on the roller and do not contact with the transparent member and document during the conveyance of the document past the roller to keep the roller clean. It is thus possible to obtain a stable reference white level signal for a prolonged period of time with the use of the light which originates from the light source and is reflected from the unenlarged white sections of the roller.