CIE Division 8 - TC8-03: Survey of Gamut Mapping Papers

Herzog & Müller (1997)

The gamut mapping algorithms proposed here were evaluated by mapping between media with the same lightness ranges. No lightness compression was therefore necessary, the hue angle of colours was kept unchanged and the following chroma mapping methods were evaluated:
(a) Piecewise linear compression along lines of constant lightness and hue angle as proposed by Gentile et al. (1990).
1.) Piecewise linear compression along the same lines, which leaves part of the range (between zero and a chosen chroma) unchanged and compresses the rest of the range more heavily.
2.) Non-linear compression along the lines of soft-clipping proposed by Stone and Wallace (1991) using the following formula:
 

Here r and o represent the reproduction and original respectively, l is a parameter, whereby the function results in clipping when l = 1 and linear compression when l = 0 and C*max = C*r(max)/C*o(max).
3.) Compression towards L*=50 on lightness axis.
4.) Mapping whereby colours with a lightness larger than L*0 were compressed towards L*0 on the lightness axis and colours with a smaller lightness were compressed along lines of constant lightness or vice versa, whereby L*0 was either 50 or the lightness of the reproduction cusp.
5.) Two-step mapping where a colourís chroma is first compressed to a certain value after which the colour is mapped towards L*=50 on the lightness axis.

These methods were experimentally studied using the pair comparison technique by evaluating reproductions made by mapping between two printed media. It was found that if lightness is held constant, clipping along lines of constant lightness and hue angle gave the best results. Indeed this is in line with a number of previous studies carried out under similar circumstances (e.g. Gentile et al., 1990; Pariser, 1991). The study also suggested that highly chromatic colours with very high or very low lightnesses should be adapted in lightness (and/or hue) in order to preserve more of their chroma.  Further, the authors have also suggested that if lightness is modified, then clipping is not a good solution due to the possibility of blocking artefacts.
 

Last updated: 17 August 1999 by Jan Morovic