Patent ID: 8159726

Claim:
An image reader comprising: a reference white sheet, the reference white sheet being a substantially white member having a uniform concentration, the reference white sheet being provided under an automatic document feeding unit, the automatic document feeding unit being configured to move a document in a document carrying path, the reference white sheet being arranged, with respect to a carried document reading glass, downstream in a document carrying direction, the carried document reading glass being provided adjacent to the document carrying path; a reading unit configured to move a scanning optical system across the reference white sheet to read the reference white sheet from a direction along which the scanning optical system returns to the carried document reading glass before reading one sheet of a document mounted on the carried document reading glass by the automatic document feeding unit in a sheet document reading mode, the scanning optical system being configured to face the carried document reading glass while reading the one sheet, the sheet reading mode includes forming an image of the document carried by the automatic document feeding unit by using an image sensor which is configured to receive light from the scanning optical system facing the carried document reading glass; and a shading correction unit that executes shading correction of eliminating irregularities in a light amount distribution in the scanning optical system based on image data obtained by reading the reference white sheet, wherein the image sensor is a plurality of color image sensors configured to sense color and the plurality of color image sensors are arranged at preset intervals and in the sheet reading mode the plurality of color image sensors acquire image data corresponding to their respective color, and in the sheet document reading mode, the shading correction unit executes the shading correction based on information obtained by moving the scanning optical system across the reference white sheet towards the carried document reading glass so that an order of data read by the plurality of color image sensors while the scanning optical system moves across the reference white sheet is the same as an order of data read by the plurality of color image sensors when the document is being read.