CIE
Division 8 - TC8-03: Survey of Gamut Mapping Papers
Gentile, Walowit & Allebach
(1990)
Both clipping and compression techniques are described in this paper and
for both kinds the gamut mapping environment is either RGB or CIELUV. In
terms of clipping algorithms two possibilities are looked at: clipping
to the closest colour in terms of *E and clipping to such a colour, which
is closest when one or more attributes are kept constant (i.e. lightness,
chroma, saturation or hue angle). Two compression algorithms were also
investigated: compression along lines of constant lightness and hue angle
and compression along lines of constant saturation. In addition to looking
at linear compression along a given line, piecewise linear compression,
which varied the slope of two segments joined at the point having the value
of the reproduction range was also investigated (Figure 1). These piecewise
linear functions were labelled with a l value which represented the normalised
distance of the connection point from the linear compression function.
A psychophysical experiment looking at the preference of gamut mapped
images was conducted to test a number of algorithms. To this end, three
images were used and gamuts of different sizes were simulated on screen.
The results suggested that clipping is preferred to compression and that
lightness and hue angle are more important than chroma and saturation.
However, it needs to be seen how well the results of an experiment which
uses synthetic gamuts and simulates a reproduction medium on the original
medium correlate with the performance of GMAs on real reproduction media.
Further it needs to be noted that the compression of lightness is not addressed
in this paper and different methods for this could also have an effect
on the results of the discussed mappings. Nonetheless, the range of chroma
and saturation compressions suggested here is a very good one and well
worth investigating in future.
Figure 1 Piecewise linear compression functions.
Last updated: 17 August 1999 by Jan
Morovic