Patent ID: 8755701

Claim:
An image scanner comprising: a light source that irradiates, with light, a recording medium on which an image is formed; a light receiving portion that receives light reflected by the recording medium; a generating portion that generates a light amount value from the light received by the light receiving portion; a measuring portion that is rotatable about a longitudinal axis thereof in which a plurality of reflecting surfaces are disposed, the reflecting surfaces respectively having predetermined colors different from each other, wherein at least one of the reflecting surfaces includes a plurality of color patches provided on a color reference plate and wherein at least one of the reflecting surfaces includes a white reference plate; and a processing portion that derives (1) a first correlation formula from a predetermined light amount value and from a light amount value generated when the white reference plate and the color reference plate are irradiated with the light from the light source, the correlation formula expressing differences between devices in scanning a light amount value; and (2) a second correlation formula using light amount data generated from a light amount value generated at a predetermined reference time and from a light amount value generated when the white reference plate and the color reference plate are irradiated with the light from the light source, the correlation formula expressing a time-varying change in the light source, wherein the color reference plate and white reference plate have reflectances different from each other.