This invention has as its object to generate image data having a desired resolution by a small footprint upon execution of resolution conversion processing in an image processing apparatus having an area image sensor. This invention is an image processing method for processing a plurality of image data which have phase shifts in the main scanning direction and sub scanning direction, including a step of inputting a target resolution, a step of executing super-resolution processing for respective positions using image data, corresponding to each position of the document in the sub scanning direction, of the plurality of image data, and a step of further executing variable-magnification processing of the image data which has undergone the super-resolution processing at that position when the resolution of the image data executed super-resolution processing is lower than the target resolution.