1. A method of sharpening a digital image having image pixels values, comprising the steps of: a) determining a D min value, representing a value corresponding to a minimum possible exposure for a system that produced the digital image; b) for each pixel value in the digital image providing a gain factor that is dependent on the difference between the pixel value and the D min value, such that pixel values nearer the D min value have smaller gain factors; and c) using the gain factors to sharpen the digital image.