CIE
Division 8 - TC8-03: Survey of Gamut Mapping Papers
Braun & Fairchild (1999)
Linear lightness rescaling techniques globally reduce the image contrast
and shift the mean lightness of the image. As the dynamic range of the
destination device decreases this effect becomes more pronounced. Often,
a lighter, "milky", low contrast reproduction results from the linear rescaling.
What is suggested to overcome this effect are "sigmoidal" lightness remapping
functions that selectively boost the contrast of the image to account for
the reduction in perceived contrast when the full dynamic range image is
mapped into the reduced output dynamic range. Using an empirically based
model, the forms of these sigmoidal remapping functions are tuned to the
characteristics of the lightness histograms of the source images and the
lightness ranges of the destination devices.
The results of this study suggest that it is possible to maintain the
perceived lightness contrast of the reproduced image by applying sigmoidal
remapping functions. The process essentially works on the basis of simultaneous
image contrast. By selectively making the high lightness colours lighter
and making the low lightness colours darker the perceived lightness dynamic
range of the reproduction is increased to be more similar to that of the
source device. This process is reported to be very robust across various
input images (i.e., with a variety of lightness histograms) and a large
range of destination device dynamic ranges.
Last updated: 17 August 1999 by Jan
Morovic