Patent ID: 7768671

Claim:
A method for controlling image gamut expansion in a document processing system including at least one processor, comprising: converting RGB values of a received document to a luminance-chrominance color space defined by a first set of Y,C 1 ,C 2 parameter values for each pixel in an original image of the received document, the first set of Y,C 1 ,C 2 parameter values including an original luminance value Y, an original chroma value C 1 , and an original hue value C 2 ; applying a gamut expansion function to occupy a greater fraction of a device gamut, including: applying the gamut expansion function to the first set of Y,C 1 ,C 2 parameter values to obtain modified Y′,C 1 ′,C 2 ′ values for a modified image including a first modified luminance value Y′, a first modified chroma value C 1 ′, and a first modified hue value C 2 ′; applying a first gamut mapping G 1 to the modified image, including: obtaining a second set of modified Y″,C 1 ″,C 2 ″ values by moving out-of-gamut pixels of the modified image to a nearest gamut plane, the second set of modified Y″,C 1 ″,C 2 ″ values including a second modified luminance value Y″, a second modified chroma value C 1 ″, and a second modified hue value C 2 ″; applying a standard pixel-wise gamut mapping to the modified image; obtaining a luminance difference output ΔY by comparing the first modified luminance value Y′ to the second modified luminance values Y″; filtering the luminance difference output ΔY of the modified image to obtain a filtered output ΔY′; obtaining an adjusted luminance value Y′″ by adding the filtered output ΔY″ to the first modified luminance value Y′; and, applying a second gamut function G 2 to obtain a third set of modified values Y″″,C 1 ′″,C 2 ′″.