Method for determining sampling timing and image reading apparatus using the same

A method for determining a sampling timing in an image reading apparatus which includes a photoelectric converter that converts image data obtained by optically reading a document into an electric signal and outputs the image data and a sampling unit that samples the output signal of the photoelectric converter at a predetermined timing, the method comprising:

• generating a plurality of sampling signals having different phases to sample a level of an output signal of the photoelectric converter;
• comparing signal levels of the output signals of the photoelectric converter, in a sampling order, each of the signals obtained by sampling, using a respective sampling signal, 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 method for determining a sampling timing in an image reading apparatus which includes a photoelectric converter that converts image data obtained by optically reading a document into an electric signal and outputs the image data and a sampling unit that samples the output signal of the photoelectric converter at a predetermined timing, the method comprising:

• setting a plurality of phases of a sampling signal used for sampling a signal level of the output signal of the photoelectric converter;
• comparing signal levels of the output signal of the photoelectric converter, in a sampling order, each of the signals obtained by sampling, using a respective sampling signal set in the setting step, so as to determine an optimum phase of the plurality of the sampling signals when a variation of signal levels being compared is at a minimum.