Patent ID: 8831443

Claim:
An image forming apparatus comprising: a plurality of color sensors; a reference plate for adjusting output characteristics of the plurality of color sensors; a reading means for causing a first color sensor of the plurality of color sensors and a second color sensor other than the first color sensor to read the density on a surface of a pre-selected kind of paper when, as a result of the first color sensor among the plurality of color sensors having obtained the readings of the reference plate, the difference between a predefined absolute value of the reference plate and readings of the reference plate read by the first color sensor is larger than a predefined threshold, and as a result of the second color sensor among the plurality of color sensors having obtained the readings of the reference plate, the difference between a predefined absolute value of the reference plate and readings of the reference plate read by the second color sensor is smaller than a predefined threshold; and a determination means for determining that there exists abnormality in the reference plate when the difference between the readings of the paper read by the first color sensor and that read by the second color sensor is smaller than a predefined threshold and determining that there exists abnormality in the first color sensor when the difference between the readings of the paper read by the first color sensor and that read by the second color sensor is larger than a predetermined threshold; and a notification means for notifying the determination result.