1. An image processing method of generating an output image of a resolution higher than a resolution of an input image, using the input image, said method comprising: obtaining an edge strength of one of the input image and an image corresponding to the input image; calculating, based on the edge strength, J that is a count of data items to be used for generating a synthesized image to be used in generating the output image, where J is an integer equal to or larger than 2; and generating the synthesized image by synthesizing J data items, and generating the output image using the synthesized image.