1. A method for enhancing an input image to produce a contrast enhanced output image, the method comprising: producing a contrast value for each pixel in the input image, said contrast value being proportional to an intensity gradient between each respective pixel and at least one pixel adjacent said respective pixel; selecting pixels in said input image having respective contrast values that meet a first criterion, thereby forming a selected plurality of pixels; producing a frequency distribution of intensity values of said selected plurality of pixels; selecting at least one range of intensity values in said frequency distribution that meet a second criterion, thereby producing a selected range of intensity values for enhancement; producing the contrast enhanced output image by, at least one of: expanding pixel intensity values in the input image that fall within said selected range of intensity values; and compressing pixel intensity values in the input image that fall outside said selected range of intensity values.