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This chapter covers concepts that are basic to printing in color, including:

• Properties of color

• Printing techniques

• Effective use of color

• Raster images and vector graphics

• File optimization for processing and printing

If you are already familiar with color theory and digital color printing, proceed to 

files for printing.

This section introduces concepts that are basic to color theory. You will encounter some of 
these concepts (such as hue, saturation, and brightness) when you work with color in 
applications; others provide useful background information. Color is a complex topic, so 
consider this a starting point for experimentation and further research.

The human eye can see electromagnetic radiation at wavelengths between 400 nanometers 
(purplish blue) and 700 nanometers (red). This range is called the visible spectrum of light. 
We see pure 

 as intensely saturated or pure colors. Sunlight at midday, which we 

perceive as white or neutral light, is composed of light from across the visible spectrum in 
more or less equal proportions. Shining sunlight through a prism separates it into its spectral 
components, resulting in the familiar rainbow of colors illustrated in the following figure.

Like the sun, most light sources we encounter in our daily environment emit a mixture of 
light wavelengths, although the particular distribution of wavelengths can vary considerably. 
Light from a tungsten light bulb, for example, contains much less blue light than sunlight. 
Tungsten light appears white to the human eye, which, up to a point, can adjust to the 
different light sources. However, color objects appear different under tungsten light than they 
do in sunlight because of the different spectral makeup of the two light sources.

The mixture of light wavelengths emitted by a light source is reflected selectively by different 
objects. Different mixtures of reflected light appear as different colors. Some of these mixtures 
appear as relatively saturated colors, but most appear as grays or impure hues of a color.

In the 1930s, the Commission Internationale de l’Eclairage (CIE) defined a standard 

, a way of defining colors in mathematical terms, to help in the communication of color 

information. This color space is based on research on the nature of color perception. The 
following CIE chromaticity diagram is a two-dimensional model of color vision. The arc 
around the top of the horseshoe encompasses the pure, or spectral, colors from blue-violet to 
red. Although the CIE chromaticity diagram is not perceptually uniform, some areas of the 
diagram seem to compress color differences relative to others, it is a good tool for illustrating 
some interesting aspects of color vision.

By mixing any two spectral colors in different proportions, we can create all the colors found 
on the straight line drawn between them in the diagram. It is possible to create the same gray 
by mixing blue-green and red light or by mixing yellow-green and blue-violet light. This is 
possible because of a phenomenon peculiar to color vision called 

. The eye does 

not distinguish individual wavelengths of light. Therefore, different combinations of spectral 
light can produce the same perceived color. 

Purple colors, which do not exist in the spectrum of pure light, are found at the bottom of the 
diagram. Purples are mixtures of red and blue light—the opposite ends of the spectrum. 

A color can be described in terms of three varying characteristics, called the 

 color model: 

• Hue: Tint (the qualitative aspect of a color—red, green, or orange)

• Saturation: The purity of the color

• Brightness: Relative position between white and black

While the CIE chromaticity diagram illustrated earlier conveys hue and saturation, 
a three-dimensional color model is required to add the brightness component, as illustrated in 
the following figure.

Many computer applications include dialog boxes in which you choose colors by 
manipulating hue, saturation, and brightness. For example, some applications use a color 
picker that can be reconfigured according to your preference (as illustrated in the following 
figure).