1. An image processing method comprising: using a computer to perform a process of: reducing a difference of at least one of a pair of images corresponding to a parallax of both eyes, said difference is other than a geometric difference between image structures corresponding to said parallax of both eyes; wherein the difference other than the geometric difference between the image structures corresponding to the parallax of both eyes is a difference between noise components superposed on the selected pair of images; and wherein the reducing a difference comprises using a least-squares method, the least-squares method determining a minimizing constant that minimizes a residual between (1) an average data function plus a constant and (2) a data function over a region of one of the selected pair of images, and setting each pixel in said region to have the value of the average data function at said each pixel plus the minimizing constant; wherein said average function is determined based on the selected pair of images.