Correction of brightness of image data outputted by an image sensor which includes a light emitting portion, a photoelectric conversion portion in which a plurality of photoelectric transducers are arrayed in line, and a charge transfer portion. For a smear occurred at the charge transfer portion, reference smear amount data is stored, corresponding to each of color components of light from the light emitting portion and a correction target pixel. A correction amount for brightness is based on a difference between brightness values of a first color component and a second color component and the reference smear amount data.