This is the first paper which does not assume that an overall uniform
lightness compression needs to be applied as the first step of gamut mapping
(though lightness compression might have been omitted due to there being
no significant lightness range difference between original and reproduction
gamuts). Instead, a method is suggested here whereby (in a plane of constant
hue angle) colours are mapped towards three different centres of gravity
depending on where they are relative to the colour K which has the lightness
of the reproductionís cusp and can have different chroma values (Figure
1).
K divides the input gamut into three regions: A - the colorimetric region where colours are reproduced exactly in terms of CIELAB, B - the region where colours are compressed towards K, C - the shadow region where colours are compressed towards the white point and D - the highlight region where colours are compressed towards the minimum lightness point of the reproduction medium on the L* axis.
This is only one of the methods described in the paper, which also deals
with their evaluation. Unfortunately, the paper was only published in Japanese
and the present review is based on private communication with one of the
authors (Katoh, 1998).