Patent ID: 8000554

Claim:
A method of controlling contrast in digital printing comprising: (a) scanning a document to be copied and printed and generating a digital image thereof; (b) mapping a pixel count and pixel values on a scale for a range of pixel values in the image between a black point and a white point range of pixel values for the image; (c) performing a linear transformation of the mapped values over said range; (d) selecting a portion of said range and performing a non-linear transformation outside said portion; and, (e) altering the image contrast for each pixel in the image based upon the non-linear transformation, a computed adjustment factor and a correction factor obtained from a look-up table; wherein the adjustment factor is computed by: V g/o =( V input −black point)*255/(white point−black point); delta= V g/o −V input ; V out =V input +m *delta; where V g/o , is the change in gain; V input is a value of a pixel; where the factor m is determined from a look-up table of selected transformation values; where V out is the adjustment factor.