Patent ID: 6952285

Claim:
An image reading device comprising: an image reading unit comprising a plurality of optical reading sensors aligned in a row, the image reading unit outputting an image signal based on an image read by the plurality of optical reading sensors; a characteristic storage unit that stores the characteristic of the image reading unit in the form of a reference image signal level curve and one of a predetermined coefficient and a threshold level curve, the reference image signal level curve being obtained by correcting an image signal curve outputted by the reading unit when the optical reading sensors read an image of a predetermined white reference member at a factory so that a peak value of the image signal curve matches a predetermined maximum readable range, and the threshold level curve being obtained by multiplying the reference image signal level curve by the predetermined coefficient; a correction coefficient calculator that produces a corrected image signal level curve by incrementally increasing a correction coefficient until, when the present image signal level curve is multiplied by the correction coefficient, at least a part of the present image signal level curve matches a part of the reference signal level curve; and a correction output unit that produces a binary output signal of the corrected image signal level curve by comparing the corrected image signal level curve with either the threshold level curve stored in the characteristic storage unit or a threshold level curve obtained by multiplying the reference image signal level curve by the predetermined coefficient.