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Tyner indb
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Bog'liq Judith A. Tyner. Principles of map design. New York. „The Guilford Press”, 2010the nAtURe of coloR
When we speak of “color” we are actually referring to the eye and brain reaction to
a part of the electromagnetic spectrum (Figure 4.1). The electromagnetic spectrum is
all energy that moves with the speed of light. It includes radio waves, x-rays, infrared
waves, ultraviolet waves, microwaves, and what we refer to as the visible spectrum.
Only a very small portion of the electromagnetic spectrum is visible to the human
eye. This portion is called the visible spectrum and includes energy with wavelengths
from 0.4 to 0.7 micrometers (µm). (A micrometer is one-millionth of a meter.) Light
waves that have a length of 0.45 µm appear blue to us; those that have a length of
0.65 µm appear red. If a light source emits waves of all these lengths, the combina-
tion appears to have no color and is called white light. Light from the sun contains
all the wavelengths. If white light is broken into its components, as with a prism or
a raindrop, then we see a rainbow with the hues of the visible spectrum displayed in
spectral order, from the shortest to longest wavelengths of violet, indigo, blue, green,
yellow, orange, and red (Figure 4.2).
If light from single-hue sources of green, red, and blue are combined, the result
is white light. Because these three wavelengths in various combination can produce
any other hue of the visible spectrum or white, they are called primaries. Since the
other hues are formed by adding the different wavelengths, they are called additive
primaries (Figure 4.3 and Plate 4.1). The colors on a television screen or color moni-
tor are formed by the additive primaries. These are used when working with maps on
a computer screen. More research is being carried out in this area.
For conventional paper maps, we do not work with colored lights, but rather
with inks or pigments on a sheet of paper. Mixing red, green, and blue pigments on
a page does not result in white, but rather in a somewhat muddy hue that approaches
black. When light strikes an opaque object, some of the light is absorbed by the
object and some is reflected. A red object absorbs all but the red light waves, which
are reflected. Pigment colors that can be combined on a page to produce all other
hues are called subtractive primaries because some of the light waves are absorbed
or subtracted by the paper. The subtractive primaries are magenta, cyan, and yellow
(Figure 4.3 and Plate 4.1). These hues, plus black, are used in printing to produce any
color or shade.
GAMMA
RAYS
X-RAYS ULTRA-
VIOLET
VISIBLE
NEAR INFRARED
SHOR
T INFRARED
MIDDLE INFRARED
THERMAL
(RED)
INFRARED
MICROWAVE
RADIOWAVES
VHF TO LF
WAVELENGTH
fIgURe 4.1.
The electromagnetic spectrum.
Color in Cartographic Design 59
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