1. An image transformation method, for an image display device, the method comprising: obtaining a 2 dimensional (2D) image and a corresponding depth image; according to the depth image and N gain values GMW, performing a motion process on the 2D image to obtain N motion images, wherein a pixel motion value in each of the motion images varies with the corresponding gain value GMW, N and w are positive integers, and 1≦w≦N; respectively performing an interpolation process on the motion images to obtain a plurality of corresponding view images; and performing a synthesis process on the view images to obtain a 3D image, wherein a formula used in performing the motion process to calculate the pixel motion values in the motion images is as follows: Sw(i,j)=(D(i,j)/a)*GMw, wherein Sw(i,j) represents the pixel motion value of the wth motion image, (i,j) represents coordinates of a pixel at the ith column and jth row in the wth motion image, D(i,j) represents a pixel value of the depth image, a is a constant, and i and j are positive integers.