1. An image processing method, comprising: upscaling an input image to a first image by a factor of n according to an upscaling algorithm; downsampling the first image to a second image by the factor of n; upscaling the second image to a third image by a factor of n according to the upscaling algorithm; subtracting the third image from the input image so as to obtain a first difference image; upscaling the first difference image to a second difference image by a factor of n according to the upscaling algorithm, further comprising: allocating the first difference image to an intermediate image according to a color filter matrix; and interpolating the intermediate image to the second difference image according to an interpolation algorithm, wherein sizes of the intermediate image and the second difference are each n times greater than a size of the input image; and summing the first image and the second difference image to an output image, wherein n is a positive integer.