1. A method of producing a tone scale function which can operate on a source digital image to improve tonal characteristics, comprising the steps of: a) receiving a source digital image including a plurality of pixels; and b) producing a tone scale function having a highlight tone scale segment and a shadow tone scale segment defined relative to a reference point on the tone scale function, and that is adapted to operate on the source digital image to improve its tonal characteristics, wherein: i) the highlight tone scale segment is defined by a different mathematical function than the shadow tone scale segment; ii) at least one of the highlight tone scale or shadow tone scale segments have at least one inflection point; iii) the highlight tone scale segment is defined for points that are equal to or greater than the reference point; and iv) the shadow tone scale segment is defined for points that are equal to or less than the reference point.