CIE
Division 8 - TC8-03: Survey of Gamut Mapping Papers
Tsumura, Imai, Saito, Haneishi & Miyake (1997)
Unlike the other papers on gamut mapping, this one is concerned with their
objective (computational) evaluation by means of calculating colour differences
between original and gamut mapped images. However, instead of using conventional
colour difference formulæ using simple Euclidean distance (e.g. *E*ab),
the approach taken here is to use Mahalanobis distance (Duda and Hart,
1973), which takes into account the correlation between differences in
individual colour attribute predictors (i.e. L*, C* and hab in CIELAB),
as a colour difference metric. Simple gamut mapping algorithms using either
lightness compression, chroma compression or a combination of these were
evaluated in the context of visualising endoscopic images on a CRT in a
lit room, whereby the technique resulting in the smallest Mahalanobis distances
was considered to be most suitable for this application.
Psychophysical experiments were performed to find a covariance matrix
to define the Mahalanobis distance for four endoscopic images. For this
purpose, the lightness of endoscopic images was changed by -4, -2, 0, 2,
4 units, the chroma was changed by -6, -3, 0, 3, 6 units, and the hue angle
was changed by -2, -1, 0, 1, 2 degrees from the original images. Every
possible combination of these three color attributes was generated and
this resulted in 125 images for each endoscopic image. Each image was displayed
randomly with the original image and ten observers were asked to view each
pair on CRT and to judge whether the two images had a noticeable difference
or not.
This results of this study suggested that it is better to adjust metric
lightness and chroma simultaneously and maintain the hue angle unchanged
to minimise changes of color appearance when reproducing endoscopic images.
Last updated: 17 August 1999 by Jan
Morovic