Gamut Mapping in Munsell Constant Hue Sections

The problem of gamut mapping is of interest in achieving an optimum color reproduction whenever a translation from one device (source) to another device (destination) is requested and the source gamut differs from destination gamut. For printing applications, if the ICC profile specifications are used, gamut mapping is applied to build the color tables that characterize the printing device. Within this approach, the color reproduction performance depends (among other factors) on the ability of the profile to include an efficient mapping method between the device independent color space (referred as the profile connection space, or PCS) and the reproduction device space. In order to map the out of gamut colors to the colors that can be reproduced on an output device, several mapping methods have been proposed. Most of them use a constant angle section in the CIELAB color space [1-6]. Within this section, different strategies can be used according to the reproduction intent. However the constant angle section in the CIELAB space only approximates the constant perceptual hue. Several studies reported perceptual hue shifts along constant angle section in CIELAB [4-6]. This is why, mapping in constant hue angle in CIELAB space may not give satisfactory performances for certain hue values. Figure 1 shows in CIELAB space the perceptual hue shift with the variation of lightness [7]. The oblique lines (i.e. segment (1)-(2)) drawn on the exterior of the hue circle illustrate the hue shift in CIELAB for different lightness levels. The end of the oblique segment closer to the achromatic center of CIELAB section points to the Munsell hue for lightness 2 to 4 (i.e. marked as (1)). The other end of the oblique segment (marked as (2)) points to the same Munsell hue for the lightness 6 to 8. As the segment deviates more from the direction of a hue, the hue shift is larger. For example, the constant hue angle for Munsell 5P hue covers 7 degrees in the CIELAB (a*, b*) plane with the variation of Munsell lightness from 4 to 8. Performing gamut mapping in CIELAB constant angle section can result in perceptual hue error. This error is larger if the mapping procedure modifies the lightness of the mapped color. To overcome the hue shift, we proposed to perform the gamut mapping in a more uniform space. We pick up for this experiment a space that results from re-mapping the CIELAB coordinate system based on the constraints imposed by the Munsell renotation system. In the Munsell renotation system the colors progress from top to bottom