An image reading method and apparatus. A reader is mounted and reads one side of an original document being conveyed at a reading position. A contact glass includes a surface contacting the original document. A reference is disposed at a side of the contact glass opposite to the surface and movable between the reading position and a standby position. The reference includes a surface facing the reader which has a predetermined color for providing shading data used for a shading correction. A carrier moves the reference to the reading position. The reader obtains the shading data by reading the predetermined color on the surface of the reference at the reading position.