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Chapter 11 ∣ Color
Copyright Goodheart-Willcox Co., Inc.
formed by this curve. Connecting the spectrum
locus curve endpoints forms a line called the purple
line, or the purple boundary. Colors on this line are
mixtures of pure violet (380 nm) and red (770 nm)
light, Figure 11-19B.
The colors plotted on the chromaticity diagram
are relative to the light source used. The A, C,
D
50
, and D
65
labels in Figure 11-19A represent the
location of the CIE standard light sources. The CIE
values of dominant wavelength, purity, and luminosity
are dependent on the color temperature of the light
source used in making the measurements. In the
CIE system, dominant wavelength relates to hue, and
purity relates to chroma or saturation.
CIELAB
In 1976, the CIE revised the standards to create
a more even distribution of colors. The result is
the CIELAB model, Figure 11-20. The distance
between colors corresponds to perceived color
differences. The CIELAB model is the current
standard for measuring the color of light and is very
similar to Munsell’s color model.
The CIELAB color space separates color and
luminance into discrete color space dimensions.
These dimensions are represented by the
designations L, A, and B.
• L. The first dimension, which represents
lightness. All colors of the same lightness lie in
a plane. Lightness varies vertically.
• A. Indicates the red to green value. Positive a*
values (+a*) appear reddish and negative a*
values (–a*) appear greenish.
• B. Represents the yellow to blue value. Positive
b* values (+b*) are yellowish and negative b*
values (–b*) are bluish.
The a* and b* designations both represent a two-
dimensional color subspace.
The human visual system is more sensitive to
the L dimension, so digital systems allocate more
data space to it than to the color components.
This allows even more efficient coding of the color
values. Using the LAB color gamut is the only true
way to accurately describe color that is device-
independent.
The Pantone® System
The Pantone system of color specification is
widely used in the graphic communications industry.
Unlike the HVC or HSB color models, the Pantone
system is not based on equal visual differences
in color. The colors used are based on ink colors
common to the printing industry.
Manuals and swatchbooks provide Pantone
color representations, names, and mixing formulas,
Figure 11-21. The colors are usually presented
on both coated and uncoated paper. Using the
manuals or swatchbooks, designers, clients,
and printers can effectively communicate color
selections. The swatchbooks and the accuracy of
their color depend on the paper, the press, and the
age of the book itself.
For years, displaying the Pantone inks on
your monitor and printing to your desktop printer
were unreliable ways to represent the inks. The
libraries in the software programs that defined the
colors used different lookup tables, all in CMYK
format, which made proofing inconsistent. The
newer Pantone Plus series has changed how they
define the colors. Using LAB values to define the
colors, these spot colors provide a more accurate
representation of the actual Pantone inks, and are
consistent throughout applications and devices,
including desktop and mobile. It is important to
make sure you have properly communicated with
all parties involved in a project when using Pantone
colors.
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Figure 11-20. The CIELAB color space defines color based
on our visual system’s perception of color.