1. A method for processing a source digital image, comprising using a processor or computer to perform steps of: accessing the source digital image comprised of a plurality of pixels; applying a spatial filter to the source digital image to produce an enhanced digital image, wherein the spatial filter changes pixel values of the source digital image based on neighboring pixel values in the source digital image; applying an inverse spatial filter to the enhanced digital image to produce an estimated digital image, wherein the inverse spatial filter changes pixel values of the enhanced digital image based on neighboring pixel values in the enhanced digital image, the inverse spatial filter being matched to the spatial filter; and producing a difference digital image from the estimated digital image and the source digital image, the difference digital image being representative of a difference between the source digital image and the estimated digital image.