Patent ID: 8427715

Claim:
An image reading apparatus that converts light reflected from an original into an analog image signal by a photoelectric conversion element, that converts the obtained analog image signal to which analog signal processing is applied into a digital image signal by an analog-digital converter, and that outputs the digital image signal, the image reading apparatus comprising: a frequency modulation unit that generates a clock whose frequency is modulated by an arbitrary modulation cycle relative to a reference clock; a modulation cycle setting unit that sets the modulation cycle; a driving unit that drives the photoelectric conversion element by the clock whose frequency is modulated; a signal generating unit that generates an analog signal corresponding to a frequency change of the clock whose frequency is modulated; an amplification inversion unit capable of amplifying an alternating current component of the analog signal with an amplification factor corresponding to a setting value set externally, and capable of switching between inversion and non-inversion; a signal superimposing unit that superimposes the analog image signal on an analog signal output from the amplification inversion unit; and a controlling unit that controls to convert the analog image signal on which the analog signal is superimposed by the signal superimposing unit into a digital image signal by the analog-digital converter, that calculates a feature amount appearing on the digital image signal based on the modulation cycle set by the modulation cycle setting unit, and that controls the amplification factor and the inversion or the non-inversion of the amplification inversion unit based on a calculation result.