1. A method of processing a digital image to produce an enhanced digital image, comprising the steps of: a) receiving a source digital image; b) receiving a rendering tone scale function wherein the rendering tone scale function is a nonlinear function that has an absolute magnitude slope in the middle of the function domain that is greater than or equal to the absolute magnitude slope at either extreme of the function domain; c) using the rendering tone scale function to calculate a de-rendering tone scale function; d) receiving or calculating an adjustment tone scale function; e) combining the de-rendering, rendering, and adjustment tone scale functions to form an enhancement tone scale function; and f) using the enhancement tone scale function and the source digital image to produce an enhanced digital image.