1. An image processing device, comprising: a central processing unit (CPU) configured to: convert a first resolution of one viewpoint image out of a first viewpoint image imaged at the first resolution to a second resolution at which a second viewpoint image is imaged, or convert the second resolution of the second viewpoint image to the first resolution, such that the first viewpoint image and the second viewpoint image have same resolution, wherein the second resolution is lower than the first resolution; generate a disparity map based on a correlation value between the first viewpoint image and the second viewpoint image that have the same resolution; and determine a pixel value of the disparity map of a target pixel based on a pixel value difference, of the first viewpoint image that has the first resolution, between the target pixel and an adjacent pixel that is adjacent to the target pixel, wherein the target pixel is a pixel that has the first resolution and is an edge region of the first viewpoint image that has the first resolution, which is other than an edge region of the first viewpoint image that has the second resolution.