Patent ID: 8837022

Claim:
An image reader comprising: a first reading unit including a first background member, to read an image on a front surface of an object to be read placed on the first background member to output a first output value; a second reading unit including a second background member to read an image on a back surface of the object placed on the second background member to output a second output value, the second background member being different from the first background member; a ground output detecting unit to detect a first ground output value that expresses an output value for a ground part of the front surface based on the first output value output by the first reading unit and a second ground output value that expresses an output value for a ground part of the back surface based on the second output value output by the second reading unit; a thickness calculating unit to calculate the thickness of the object based on an output ratio between the first ground output value and the second ground output value; and an output correction unit to correct the first output value output by the first reading unit and the second output value output by the second reading unit based on the calculated thickness of the object, to output a corrected first output value and a corrected second output value, respectively, wherein the output correction unit is used to calculate a first correction factor for the first output value and a second correction factor for the second output value based on the thickness of the object calculated by the thickness calculating unit, and to correct the first output value and the second output value based on the first correction factor and the second correction factor, respectively.