Three-Dimensional Control of Color Management Systems - Control of Color Imaging Systems: Analysis and Design - page 351

Σ

CMYK

+

CMY -

0.5 x 2

K + =x 2

x 2

CMY -

x

CMY - = x 2

1

Min

K +

x

Min ( C , M , Y )

(a) (b)

FIGURE 7.25 A simple GCR = UCR function (a) block diagram view (b) plot of GCR
function with respect to min (C, M, Y).

For example, CMY ¼ [0.5 0.3 0.4] color patch (CMY values in 0 to 1 range)

to CMYK ¼ is equivalent [0.455 0.255 0.355 0.09] patch using the above

GCR UCR algorithm. Soon it will become clear that this method has the disadvan-

tage of not producing suf

=

ciently optimized colors for the entire color gamut since
inherently the practice of starting with CMY separations and subsequently adding
black leads to loss of gamut. However, in Ref. [81] a max-gamut GCR is developed
which starts with CMY separations and still preserves the total gamut volume.
Figure 7.26 shows the comparison between the two gamuts; one gamut produced

FIGURE 7.26 CMYK gamut compared to a CMY to L*a*b* printer gamut with the simple
CMY to CMYK GCR (wire: A CMYK to L*a*b* gamut of a four-color printer; solid: a gamut
of a CMY to L*a*b* printer with GCR = UCR of Figure 7.25).