Color
Color
or colour
(see spelling
differences) is the visual
perceptual property
corresponding in humans
to the categories called red,
blue,
yellow,
green
and others. Color derives from the spectrum
of light (distribution of light
power versus wavelength)
interacting in the eye with the spectral sensitivities of the light
receptors. Color categories and physical specifications of color
are also associated with objects or materials based on their physical
properties such as light absorption, reflection, or emission spectra.
By defining a color
space, colors can be identified numerically by their coordinates.
Because
perception of color stems from the varying spectral
sensitivity of different types of cone
cells in the retina
to different parts of the spectrum, colors may be defined and
quantified by the degree to which they stimulate these cells. These
physical or physiological
quantifications of color, however, do not fully explain the
psychophysical
perception of color appearance.
The
science of color is sometimes called chromatics,
chromatography,
colorimetry,
or simply color
science.
It includes the perception of color by the human
eye and brain, the origin of color in materials, color
theory in art, and
the physics of
electromagnetic
radiation in the visible range (that is, what we commonly refer
to simply as light).
Electromagnetic
radiation is characterized by its wavelength
(or frequency)
and its intensity.
When the wavelength is within the visible spectrum (the range of
wavelengths humans can perceive, approximately from 390 nm
to 700 nm), it is known as "visible light".
Most light sources emit
light at many different wavelengths; a source's spectrum
is a distribution giving its intensity at each wavelength. Although
the spectrum of light arriving at the eye from a given direction
determines the color sensation
in that direction, there are many more possible spectral combinations
than color sensations. In fact, one may formally define a color as a
class of spectra that give rise to the same color sensation, although
such classes would vary widely among different species, and to a
lesser extent among individuals within the same species. In each such
class the members are called metamers
of the color in question.