Patent ID: 8264747

Claim:
An image reading device comprising: a light source that illuminates an original; an image sensor that receives a light reflected from the original and outputs an image signal corresponding to the light in synchronization with an input of a timing signal at a plurality of timings; a timing generating unit that generates a sampling-and-holding timing based on the timing signals; a sampling-and-holding circuit that generates a plurality of analog image signals by sampling the image signal at each sampling-and-holding timing and holding sampled image signals for a predetermined amount of time, and outputs the analog image signals; an analog-to-digital converting unit that performs signal quantization of the analog image signals to obtain a plurality of digital image signals at each sampling-and-holding timing and outputs the digital image signals; a phase regulating unit that performs phase regulation of each sampling-and-holding timing based on corresponding digital image signals to obtain phase-regulated sampling-and-holding timing; and an image processing unit that performs image processing on the digital image signals obtained at an optimal phase-regulated sampling-and-holding timing, wherein the sampling-and-holding circuit generates the analog image signal at each phase-regulated sampling-and-holding timing, the image reading device further comprising a calculating unit that calculates an n-th mean value of the digital image signals at an n-th sampling-and-holding timing, an (n−1)-th mean value of the digital image signals at an (n−1)-th sampling-and-holding timing, and an (n+1)-th mean value of the digital image signals at an (n+1)-th sampling-and-holding timing, calculates a first difference between the n-th mean value and the (n−1)-th mean value, and a second difference between the n-th mean value and the (n+1)-th mean value, calculates a sum of the first difference and the second difference to obtain a sum of differences at the n-th sampling-and-holding timing, and repeats calculating the sum of differences at each sampling-and-holding timing, wherein the phase regulating unit selects a sampling-and-holding timing at which the sum of differences is minimum as the optimal sampling-and-holding timing.