Image reading apparatus and image forming apparatus

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.