Patent ID: 7726569

Claim:
An image reading apparatus comprising: a photoelectric converter that converts image data obtained by optically reading a document into an electric signal and outputs the image data; a clock controller that generates a plurality of sampling signals having different phases to sample a level of an output signal of the photoelectric converter; a phase determination unit that compares signal levels in a sampling order, each of the signals obtained by sampling, using a respective sampling signal, the output signal of the photoelectric converter, so as to determine an optimum phase of the plurality of the sampling signals when a condition is fulfilled in which an absolute value of a variation between signal levels being compared is less than a threshold value and stops comparing subsequent signal levels in the sampling order; a storage unit in which the optimum phase determined by the phase determination unit is stored; and a sampling unit that samples the output signal of the photoelectric converter using the sampling signal having the optimum phase stored in the storage unit.