US Patent 7408682 Image reading apparatus

In an image reading apparatus according to the invention, the switching frequency of a switching power supply is set to a value equal to integral multiples of a reading frequency corresponding to each line, thereby correcting, for example, uneven image density due to ripples in a power supply voltage. Further, the switching of the switching power supply is synchronized with a horizontal synchronizing signal output from a scanner, thereby causing the positions of the ripples to correspond between lines for correcting, for example, uneven image density.