1. An image generation method for generating an output image from a plurality of input images captured at a plurality of viewpoints by an image sensor, the method comprising: a step of generating a plurality of pixel shifted images by performing different shifting for each of the plurality of input images according to a virtual image forming plane that is different from an image sensing plane at which the input images are captured, wherein an amount of pixel shifting is non-integral; and a step of generating an output image that has a higher resolution than the resolution of the input images from the plurality of pixel shifted images through composition processing.