PSYCHOPHYSICAL EVALUATION OF GAMUT MAPPING TECHNIQUES USING SIMPLE RENDERED IMAGES AND ARTIFICIAL GAMUT BOUNDARIES

Using a paired comparison paradigm, various gamut mapping algorithms w ere evaluated using simple rendered images and artificial gamut bounda ries, The test images consisted of simple rendered spheres floating in front of a gray background, Using CIELAB as our device-independent co lor space, cut-off values for lightness and chroma, based on the stati stics of the images, were chosen to reduce the gamuts for the test ima ges, The gamut mapping algorithms consisted of combinations of clippin g and mapping the original gamut in linear piecewise segments, Complet e color space compression in RGB and CIELAB was also tested, Each of t he colored originals (R,G,B,C,M,Y, and Skin) were mapped separately in lightness and chroma, In addition, each algorithm was implemented wit h saturation (C/L*) allowed to vary or retain the same values as in t he original image, Pairs of test images with reduced color gamuts were presented to twenty subjects along with the original image. For each pair the subjects chose the test image that better reproduced the orig inal, Rank orders and interval scales of algorithm performance with co nfidence limits were then derived, Clipping all out-of-gamut colors wa s the best method for mapping chroma, For lightness mapping at low lig htness levels and high lightness levels particular gamut mapping algor ithms consistently produced images chosen as most like the original, T he choice of device-independent color space may also influence which g amut mapping algorithms are best.