Patent ID: 7989748

Claim:
An image reading apparatus comprising: an image sensor in which a shift register for transferring electric charge from photodiodes is divided into a first half and a second half, from which image data is output in respective corresponding output directions; a linearity correcting part correcting linearity between image data obtained from the first half and the second half; a level detecting part detecting image data levels for the respective output directions of the first half and the second half to be used for the linearity correction, which image data levels correspond to image data of a connection point between the first half and the second half and are obtained from respective combinations for the respective output directions of the first half and the second half; a calculating part calculating linearity correction values or correction value calculating parameters from the detected image data levels for any one of the first half and the second half; and a defect detection part detecting a defect in the image data levels thus detected of the connection point.