Color (
American English
American English, sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. English is the Languages of the United States, most widely spoken lan ...
) or colour (
British English) is the
visual perceptual property deriving from the
spectrum of light interacting with the
photoreceptor cell
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiatio ...
s of the eyes. Color categories and physical specifications of color are 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
Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cones ...
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
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
quantifications of color, however, do not fully explain the
psychophysical perception of color appearance.
Color science includes the
perception of color
Color vision, a feature of visual perception, is an ability to perceive differences between light composed of different wavelengths (i.e., different spectral power distributions) independently of light intensity. Color perception is a part of t ...
by the
eye
Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...
and brain, the origin of color in materials,
color theory
In the visual arts, color theory is the body of practical guidance for color mixing and the visual effects of a specific color combination. Color terminology based on the color wheel and its geometry separates colors into primary color, seconda ...
in
art, and the
physics of
electromagnetic radiation in the visible range (i.e. ''
light'').
Physics of color
Electromagnetic radiation is characterized by its
wavelength (or
frequency) and its
intensity
Intensity may refer to:
In colloquial use
*Strength (disambiguation)
*Amplitude
* Level (disambiguation)
* Magnitude (disambiguation)
In physical sciences
Physics
*Intensity (physics), power per unit area (W/m2)
*Field strength of electric, ma ...
. 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. This effect can be visualized by comparing the light sources'
spectral power distribution
In radiometry, photometry, and color science, a spectral power distribution (SPD) measurement describes the power per unit area per unit wavelength of an illumination (radiant exitance). More generally, the term ''spectral power distribution'' ...
s and the resulting colors.
Spectral colors
The familiar colors of the
rainbow in the
spectrum—named using the
Latin word for ''appearance'' or ''apparition'' by
Isaac Newton in 1671—include all those colors that can be produced by visible
light of a single wavelength only, the
''pure spectral'' or ''monochromatic'' colors. The table at right shows approximate frequencies (in
terahertz
Terahertz or THz may refer to:
* Terahertz (unit), a unit of frequency, defined as one trillion (1012) cycles per second or 1012 hertz
* Terahertz radiation, electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3 terahe ...
) and wavelengths (in
nanometer
330px, Different lengths as in respect to the molecular scale.
The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...
s) for spectral colors in the visible range. Spectral colors have 100%
purity, and are fully
saturated. A complex mixture of spectral colors can be used to describe any color, which is the definition of a light
power spectrum.
The color table should not be interpreted as a definitive list; the spectral colors form a continuous spectrum, and how it is divided into
distinct colors linguistically is a matter of culture and historical contingency. Despite the ubiquitous
ROYGBIV mnemonic used to remember the spectral colors in english, the inclusion or exclusion of colors in this table is contentious, with disagreement often focused on
indigo and cyan. Even if the subset of color terms is agreed, their wavelength ranges and borders between them may not be.
The ''intensity'' of a spectral color, relative to the context in which it is viewed, may alter its perception considerably according to the
Bezold–Brücke shift; for example, a low-intensity orange-yellow is
brown, and a low-intensity yellow-green is
olive green.
Color of objects
The color of an object as perceived by an observer is not an intrinsic quality of that object, but depends on several factors:
# the physics of the object (which wavelengths of light are selectively absorbed, reflected, transmitted, or emitted)
# the color of the light shining on the object (
color cast
A colour cast is a tint of a particular colour, usually unwanted, that evenly affects a photographic image in whole or in part.
Certain types of light can cause film and digital cameras to render a colour cast. Illuminating a subject with light s ...
of the
illuminant)
# the angles between observer, object and illuminant (applicable to
structural color)
# the physics of light in its environment (how the atmosphere may affect the light through
Rayleigh scattering or
dispersion, for example)
# relative velocity between object and observer (
red shift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in fr ...
; mostly applicable to astronomy)
# the characteristics of the perceiving eye (the number and
spectral sensitivity of
cone classes and
dimensionality of color vision)
# higher order processes in the brain that affect the color, such as
color constancy
Some generalizations of the physics can be drawn, neglecting perceptual effects for now:
*Light arriving at an
opaque surface is either
reflected Reflection or reflexion may refer to:
Science and technology
* Reflection (physics), a common wave phenomenon
** Specular reflection, reflection from a smooth surface
*** Mirror image, a reflection in a mirror or in water
** Signal reflection, in ...
"
specularly" (that is, in the manner of a mirror),
scattered
Scattered may refer to:
Music
* ''Scattered'' (album), a 2010 album by The Handsome Family
* "Scattered" (The Kinks song), 1993
* "Scattered", a song by Ace Young
* "Scattered", a song by Lauren Jauregui
* "Scattered", a song by Green Day from ' ...
(that is, reflected with diffuse scattering), or
absorbed—or some combination of these.
*Opaque objects that do not reflect specularly (which tend to have rough surfaces) have their color determined by which wavelengths of light they scatter strongly (with the light that is not scattered being absorbed). If objects scatter all wavelengths with roughly equal strength, they appear white. If they absorb all wavelengths, they appear black.
*Opaque objects that specularly reflect the light of different wavelengths with different efficiencies look like mirrors tinted with colors determined by those differences. An object that reflects some fraction of impinging light and absorbs the rest may look black but also be faintly reflective; examples are black objects coated with layers of enamel or lacquer.
*Objects that
transmit light are either ''translucent'' (scattering the transmitted light) or ''transparent'' (not scattering the transmitted light). If they also absorb (or reflect) light of various wavelengths differentially, they appear tinted with a color determined by the nature of that absorption (or that reflectance).
*Objects may emit light that they generate from having excited electrons, rather than merely reflecting or transmitting light. The electrons may be excited due to elevated temperature (''
incandescence
Incandescence is the emission of electromagnetic radiation (including visible light) from a hot body as a result of its high temperature. The term derives from the Latin verb ''incandescere,'' to glow white. A common use of incandescence is ...
''), as a result of chemical reactions (''
chemiluminescence
Chemiluminescence (also chemoluminescence) is the emission of light (luminescence) as the result of a chemical reaction. There may also be limited emission of heat. Given reactants A and B, with an excited intermediate â—Š,
: + -> lozenge -> ...
''), after absorbing light of other frequencies ("
fluorescence" or "
phosphorescence") or from electrical contacts as in
light-emitting diodes, or other
light sources.
To summarize, the color of an object is a complex result of its surface properties, its transmission properties, and its emission properties, all of which contribute to the mix of wavelengths in the light leaving the surface of the object. The perceived color is then further conditioned by the nature of the ambient illumination, and by the color properties of other objects nearby, and via other characteristics of the perceiving eye and brain.
Perception
Development of theories of color vision
Although
Aristotle and other ancient scientists had already written on the nature of light and
color vision
Color vision, a feature of visual perception, is an ability to perceive differences between light composed of different wavelengths (i.e., different spectral power distributions) independently of light intensity. Color perception is a part of ...
, it was not until
Newton
Newton most commonly refers to:
* Isaac Newton (1642–1726/1727), English scientist
* Newton (unit), SI unit of force named after Isaac Newton
Newton may also refer to:
Arts and entertainment
* ''Newton'' (film), a 2017 Indian film
* Newton ( ...
that light was identified as the source of the color sensation. In 1810,
Goethe published his comprehensive ''
Theory of Colors
''Theory of Colours'' (german: Zur Farbenlehre, links=no) is a book by Johann Wolfgang von Goethe about the poet's views on the nature of colours and how these are perceived by humans. It was published in German in 1810 and in English in 1840. ...
'' in which he provided a rational description of colour experience, which 'tells us how it originates, not what it is'. (Schopenhauer)
In 1801
Thomas Young proposed his
trichromatic theory, based on the observation that any color could be matched with a combination of three lights. This theory was later refined by
James Clerk Maxwell and
Hermann von Helmholtz. As Helmholtz puts it, "the principles of Newton's law of mixture were experimentally confirmed by Maxwell in 1856. Young's theory of color sensations, like so much else that this marvelous investigator achieved in advance of his time, remained unnoticed until Maxwell directed attention to it."
At the same time as Helmholtz,
Ewald Hering developed the
opponent process theory of color, noting that
color blindness and afterimages typically come in opponent pairs (red-green, blue-orange, yellow-violet, and black-white). Ultimately these two theories were synthesized in 1957 by Hurvich and Jameson, who showed that retinal processing corresponds to the trichromatic theory, while processing at the level of the
lateral geniculate nucleus corresponds to the opponent theory.
In 1931, an international group of experts known as the ''Commission internationale de l'éclairage'' (
CIE) developed a mathematical color model, which mapped out the space of observable colors and assigned a set of three numbers to each.
Color in the eye
The ability of the
human eye
The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm.
...
to distinguish colors is based upon the varying sensitivity of different cells in the
retina to light of different
wavelengths. Humans are
trichromatic—the retina contains three types of color receptor cells, or
cones. One type, relatively distinct from the other two, is most responsive to light that is perceived as blue or blue-violet, with wavelengths around 450
nm; cones of this type are sometimes called ''short-wavelength cones'' or ''S cones'' (or misleadingly, ''blue cones''). The other two types are closely related genetically and chemically: ''middle-wavelength cones'', ''M cones'', or ''green cones'' are most sensitive to light perceived as green, with wavelengths around 540 nm, while the ''long-wavelength cones'', ''L cones'', or ''red cones'', are most sensitive to light that is perceived as greenish yellow, with wavelengths around 570 nm.
Light, no matter how complex its composition of wavelengths, is reduced to three color components by the eye. Each cone type adheres to the
principle of univariance, which is that each cone's output is determined by the amount of light that falls on it over all wavelengths. For each location in the visual field, the three types of cones yield three signals based on the extent to which each is stimulated. These amounts of stimulation are sometimes called ''tristimulus values''.
The response curve as a function of wavelength varies for each type of cone. Because the curves overlap, some tristimulus values do not occur for any incoming light combination. For example, it is not possible to stimulate ''only'' the mid-wavelength (so-called "green") cones; the other cones will inevitably be stimulated to some degree at the same time. The set of all possible tristimulus values determines the human ''color space''. It has been estimated that humans can distinguish roughly 10 million different colors.
The other type of light-sensitive cell in the eye, the
rod
Rod, Ror, Ród, Rőd, Rød, Röd, ROD, or R.O.D. may refer to:
Devices
* Birch rod, made out of twigs from birch or other trees for corporal punishment
* Ceremonial rod, used to indicate a position of authority
* Connecting rod, main, coupling, ...
, has a different response curve. In normal situations, when light is bright enough to strongly stimulate the cones, rods play virtually no role in vision at all. On the other hand, in dim light, the cones are understimulated leaving only the signal from the rods, resulting in a
colorless response. (Furthermore, the rods are barely sensitive to light in the "red" range.) In certain conditions of intermediate illumination, the rod response and a weak cone response can together result in color discriminations not accounted for by cone responses alone. These effects, combined, are summarized also in the
Kruithof curve, which describes the change of color perception and pleasingness of light as a function of temperature and intensity.
Color in the brain
While the mechanisms of
color vision
Color vision, a feature of visual perception, is an ability to perceive differences between light composed of different wavelengths (i.e., different spectral power distributions) independently of light intensity. Color perception is a part of ...
at the level of the
retina are well-described in terms of tristimulus values, color processing after that point is organized differently. A dominant theory of color vision proposes that color information is transmitted out of the eye by three
opponent processes, or opponent channels, each constructed from the raw output of the cones: a red–green channel, a blue–yellow channel, and a black–white "luminance" channel. This theory has been supported by neurobiology, and accounts for the structure of our subjective color experience. Specifically, it explains why humans cannot perceive a "reddish green" or "yellowish blue", and it predicts the
color wheel: it is the collection of colors for which at least one of the two color channels measures a value at one of its extremes.
The exact nature of color perception beyond the processing already described, and indeed the status of color as a feature of the perceived world or rather as a feature of our ''perception'' of the world—a type of
qualia—is a matter of complex and continuing philosophical dispute.
Nonstandard color perception
Color vision deficiency
A color vision deficiency causes an individual to perceive a smaller
gamut of colors than the standard observer with normal color vision. The effect can be mild, having lower "color resolution" (i.e.
anomalous trichromacy
Color blindness or color vision deficiency (CVD) is the decreased ability to color vision, see color or differences in color. It can impair tasks such as selecting ripe fruit, choosing clothing, and reading traffic lights. Color blindness may ...
), moderate, lacking an entire dimension or channel of color (e.g.
dichromacy), or complete, lacking all color perception (i.e.
monochromacy). Most forms of color blindness derive from one or many of the three classes of cone cells either being missing, having a shifted
spectral sensitivity or having lower responsiveness to incoming light. In addition,
cerebral achromatopsia is caused by neural anomalies in those parts of the brain where visual processing takes place.
Some colors that appear distinct to an individual with normal color vision will appear
metameric to the color blind. The most common form of color blindness is
congenital red-green color blindness
A birth defect, also known as a congenital disorder, is an abnormal condition that is present at childbirth, birth regardless of its cause. Birth defects may result in disability, disabilities that may be physical disability, physical, intellect ...
, affecting ~8% of males. Individuals with the strongest form of this condition (
dichromacy) will experience blue and purple, green and yellow, teal and gray as colors of confusion, i.e. metamers.
Tetrachromacy
Outside of humans, which are mostly ''trichromatic'' (having three types of cones), most mammals are dichromatic, possessing only two cones. However, outside of mammals, most vertebrate are ''
tetrachromatic
Tetrachromacy (from Greek ''tetra'', meaning "four" and ''chromo'', meaning "color") is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cell in the eye. Organisms with tetr ...
'', having four types of cones, and includes most,
birds,
reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s,
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s and
bony fish
Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...
. An extra dimension of color vision means these vertebrates can see two distinct colors that a normal human would view as
metamers. Some invertebrates, such as the
mantis shrimp
Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda (). Stomatopods branched off from other members of the class Malacostraca around 340 million years ago. Mantis shrimp typically grow to around in lengt ...
, have an even higher number of cones (12) that could lead to a richer color
gamut than even imaginable by humans.
The existence of human tetrachromats is a contentious notion. As many as
half of all human females have 4 distinct cone classes, which could enable tetrachromacy.
However, a distinction must be made between ''retinal (or weak) tetrachromats'', which express four cone classes in the retina, and ''functional (or strong) tetrachromats'', which are able to make the enhanced color discriminations expected of tetrachromats. In fact, there is only
one peer-reviewed report of a functional tetrachromat. It is estimated that while the average person is able to see one million colors, someone with functional tetrachromacy could see a hundred million colors.
Synesthesia
In certain forms of
synesthesia
Synesthesia (American English) or synaesthesia (British English) is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to involuntary experiences in a second sensory or cognitive pathway. People who re ...
, perceiving letters and numbers (
grapheme–color synesthesia) or hearing sounds (
chromesthesia) will evoke a perception of color. Behavioral and
functional neuroimaging experiments have demonstrated that these color experiences lead to changes in behavioral tasks and lead to increased activation of brain regions involved in color perception, thus demonstrating their reality, and similarity to real color percepts, albeit evoked through a non-standard route. Synesthesia can occur genetically, with 4% of the population having variants associated with the condition. Synesthesia has also been known to occur with brain damage, drugs, and sensory deprivation.
The philosopher Pythagoras experienced synesthesia and provided one of the first written accounts of the condition in approximately 550 BCE. He created mathematical equations for musical notes that could form part of a scale, such as an octave.
Afterimages
After exposure to strong light in their sensitivity range,
photoreceptors of a given type become desensitized. For a few seconds after the light ceases, they will continue to signal less strongly than they otherwise would. Colors observed during that period will appear to lack the color component detected by the desensitized photoreceptors. This effect is responsible for the phenomenon of
afterimages, in which the eye may continue to see a bright figure after looking away from it, but in a
complementary color.
Afterimage effects have also been used by artists, including
Vincent van Gogh.
Color constancy
When an artist uses a limited
color palette, the
human eye
The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm.
...
tends to compensate by seeing any gray or neutral color as the color which is missing from the color wheel. For example, in a limited palette consisting of red, yellow, black, and white, a mixture of yellow and black will appear as a variety of green, a mixture of red and black will appear as a variety of purple, and pure gray will appear bluish.
The trichromatic theory is strictly true when the visual system is in a fixed state of adaptation. In reality, the visual system is constantly adapting to changes in the environment and compares the various colors in a scene to reduce the effects of the illumination. If a scene is illuminated with one light, and then with another, as long as the difference between the light sources stays within a reasonable range, the colors in the scene appear relatively constant to us. This was studied by
Edwin H. Land in the 1970s and led to his retinex theory of
color constancy.
Both phenomena are readily explained and mathematically modeled with modern theories of chromatic adaptation and color appearance (e.g.
CIECAM02, iCAM).
[M.D. Fairchild]
Color Appearance Models
, 2nd Ed., Wiley, Chichester (2005). There is no need to dismiss the trichromatic theory of vision, but rather it can be enhanced with an understanding of how the visual system adapts to changes in the viewing environment.
Color naming
Colors vary in several different ways, including
hue (shades of
red,
orange,
yellow,
green,
blue, and
violet),
saturation,
brightness, and
gloss. Some color words are derived from the name of an object of that color, such as "
orange" or "
salmon", while others are abstract, like "red".
In the 1969 study ''
Basic Color Terms
''Basic Color Terms: Their Universality and Evolution'' (1969; ) is a book by Brent Berlin and Paul Kay. Berlin and Kay's work proposed that the basic color terms in a culture, such as black, brown, or red, are predictable by the number of color ...
: Their Universality and Evolution'',
Brent Berlin and
Paul Kay describe a pattern in naming "basic" colors (like "red" but not "red-orange" or "dark red" or "blood red", which are "shades" of red). All languages that have two "basic" color names distinguish dark/cool colors from bright/warm colors. The next colors to be distinguished are usually red and then yellow or green. All languages with six "basic" colors include black, white, red, green, blue, and yellow. The pattern holds up to a set of twelve: black, gray, white, pink, red, orange, yellow, green, blue, purple, brown, and
azure
Azure may refer to:
Colour
* Azure (color), a hue of blue
** Azure (heraldry)
** Shades of azure, shades and variations
Arts and media
* ''Azure'' (Art Farmer and Fritz Pauer album), 1987
* Azure (Gary Peacock and Marilyn Crispell album), 2013
...
(distinct from blue in
Russian and
Italian, but not English).
In culture
Colors, their meanings and associations can play a major role in works of art, including literature.
Associations
Individual colors have a variety of cultural associations such as
national colors (in general described in individual color articles and
color symbolism). The field of
color psychology attempts to identify the effects of color on human emotion and activity.
Chromotherapy is a form of
alternative medicine
Alternative medicine is any practice that aims to achieve the healing effects of medicine despite lacking biological plausibility, testability, repeatability, or evidence from clinical trials. Complementary medicine (CM), complementary and alt ...
attributed to various Eastern traditions. Colors have different associations in different countries and cultures.
Different colors have been demonstrated to have effects on cognition. For example, researchers at the University of Linz in Austria demonstrated that the color red significantly decreases cognitive functioning in men. The combination of the colors red and yellow together can induce hunger, which has been capitalized on by a number of chain restaurants.
Color plays a role in memory development too. A photograph that is in black and white is slightly less memorable than one in color. Studies also show that wearing bright colors makes you more memorable to people you meet.
Color reproduction
Color reproduction is the science of creating colors for the human eye that faithfully represent the desired color. It focuses on how to construct a spectrum of wavelengths that will best evoke a certain color in an observer. Most colors are not
spectral colors, meaning they are mixtures of various wavelengths of light. However, these non-spectral colors are often described by their
dominant wavelength, which identifies the single wavelength of light that produces a sensation most similar to the non-spectral color. Dominant wavelength is roughly akin to
hue.
There are many color perceptions that by definition cannot be pure spectral colors due to
desaturation
Desaturation may refer to:
* In pulse oximetry, the condition of a low blood oxygen concentration
* Reduction of colorfulness in image processing
* Conversion of a saturated compound
In chemistry, a saturated compound is a chemical compound (or ...
or because they are
purples (mixtures of red and violet light, from opposite ends of the spectrum). Some examples of necessarily non-spectral colors are the achromatic colors (black, gray, and white) and colors such as
pink,
tan, and
magenta.
Two different light spectra that have the same effect on the three color receptors in the
human eye
The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm.
...
will be perceived as the same color. They are
metamers of that color. This is exemplified by the white light emitted by fluorescent lamps, which typically has a spectrum of a few narrow bands, while daylight has a continuous spectrum. The human eye cannot tell the difference between such light spectra just by looking into the light source, although the
color rendering index of each light source may affect the color of objects illuminated by these metameric light sources.
Similarly, most human color perceptions can be generated by a mixture of three colors called ''primaries''. This is used to reproduce color scenes in photography, printing, television, and other media. There are a number of methods or
color spaces for specifying a color in terms of three particular
primary colors. Each method has its advantages and disadvantages depending on the particular application.
No mixture of colors, however, can produce a response truly identical to that of a spectral color, although one can get close, especially for the longer wavelengths, where the
CIE 1931 color space chromaticity diagram has a nearly straight edge. For example, mixing green light (530 nm) and blue light (460 nm) produces cyan light that is slightly desaturated, because response of the red color receptor would be greater to the green and blue light in the mixture than it would be to a pure cyan light at 485 nm that has the same intensity as the mixture of blue and green.
Because of this, and because the ''primaries'' in
color printing systems generally are not pure themselves, the colors reproduced are never perfectly saturated spectral colors, and so spectral colors cannot be matched exactly. However, natural scenes rarely contain fully saturated colors, thus such scenes can usually be approximated well by these systems. The range of colors that can be reproduced with a given color reproduction system is called the
gamut. The
CIE chromaticity diagram can be used to describe the gamut.
Another problem with color reproduction systems is connected with the initial measurement of color, or
colorimetry. The characteristics of the color sensors in measurement devices (e.g. cameras, scanners) are often very far from the characteristics of the receptors in the human eye.
A color reproduction system "tuned" to a human with normal color vision may give very inaccurate results for other observers, according to color vision deviations to the
standard observer
The CIE 1931 color spaces are the first defined quantitative links between distributions of wavelengths in the electromagnetic visible spectrum, and physiologically perceived colors in human color vision. The mathematical relationships that defin ...
.
The different color response of different devices can be problematic if not properly managed. For color information stored and transferred in digital form,
color management techniques, such as those based on
ICC profiles, can help to avoid distortions of the reproduced colors. Color management does not circumvent the gamut limitations of particular output devices, but can assist in finding good mapping of input colors into the gamut that can be reproduced.
Additive coloring
Additive color is light created by mixing together
light of two or more different colors.
Red,
green, and
blue are the additive
primary colors normally used in additive color systems such as projectors and computer terminals.
Subtractive coloring
Subtractive coloring uses dyes, inks, pigments, or filters to absorb some wavelengths of light and not others. The color that a surface displays comes from the parts of the visible spectrum that are not absorbed and therefore remain visible. Without pigments or dye, fabric fibers, paint base and paper are usually made of particles that scatter white light (all colors) well in all directions. When a pigment or ink is added, wavelengths are absorbed or "subtracted" from white light, so light of another color reaches the eye.
If the light is not a pure white source (the case of nearly all forms of artificial lighting), the resulting spectrum will appear a slightly different color.
Red paint, viewed under
blue light, may appear
black. Red paint is red because it scatters only the red components of the spectrum. If red paint is illuminated by blue light, it will be absorbed by the red paint, creating the appearance of a black object.
Structural color
Structural colors are colors caused by interference effects rather than by pigments. Color effects are produced when a material is scored with fine parallel lines, formed of one or more parallel thin layers, or otherwise composed of microstructures on the scale of the color's
wavelength. If the microstructures are spaced randomly, light of shorter wavelengths will be scattered preferentially to produce
Tyndall effect colors: the blue of the sky (Rayleigh scattering, caused by structures much smaller than the wavelength of light, in this case, air molecules), the luster of
opals, and the blue of human irises. If the microstructures are aligned in arrays, for example, the array of pits in a CD, they behave as a
diffraction grating: the grating reflects different wavelengths in different directions due to
interference phenomena, separating mixed "white" light into light of different wavelengths. If the structure is one or more thin layers then it will reflect some wavelengths and transmit others, depending on the layers' thickness.
Structural color is studied in the field of
thin-film optics. The most ordered or the most changeable structural colors are
iridescent
Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...
. Structural color is responsible for the blues and greens of the feathers of many birds (the blue jay, for example), as well as certain butterfly wings and beetle shells. Variations in the pattern's spacing often give rise to an iridescent effect, as seen in
peacock feathers,
soap bubble
A soap bubble is an extremely thin film of soap or detergent and water enclosing air that forms a hollow sphere with an iridescent surface. Soap bubbles usually last for only a few seconds before bursting, either on their own or on contact wi ...
s, films of oil, and
mother of pearl, because the reflected color depends upon the viewing angle. Numerous scientists have carried out research in butterfly wings and beetle shells, including Isaac Newton and Robert Hooke. Since 1942,
electron micrography has been used, advancing the development of products that exploit structural color, such as "
photonic" cosmetics.
Additional terms
*
Color wheel: an illustrative organization of color hues in a circle that shows relationships.
*
Colorfulness
Colorfulness, chroma and saturation are attributes of perceived color relating to chromatic intensity. As defined formally by the International Commission on Illumination (CIE) they respectively describe three different aspects of chromatic ...
, chroma, purity, or saturation: how "intense" or "concentrated" a color is. Technical definitions distinguish between colorfulness, chroma, and saturation as distinct perceptual attributes and include purity as a physical quantity. These terms, and others related to light and color, are internationally agreed upon and published in the CIE Lighting Vocabulary. More readily available texts on colorimetry also define and explain these terms.
[R.S. Berns]
Principles of Color Technology
, 3rd Ed., Wiley, New York (2001).
*
Dichromatism
Dichromatism (or polychromatism) is a phenomenon where a material or solution's hue is dependent on both the concentration of the absorbing substance and the depth or thickness of the medium traversed. In most substances which are not dichromatic, ...
: a phenomenon where the hue is dependent on the concentration and thickness of the absorbing substance.
*
Hue: the color's direction from white, for example in a
color wheel or
chromaticity diagram.
*
Shade: a color made darker by adding black.
*
Tint: a color made lighter by adding white.
*
Value, brightness, lightness, or luminosity: how light or dark a color is.
See also
*
Chromophore
A chromophore is the part of a molecule responsible for its color.
The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molec ...
*
Color analysis (art)
Color analysis (American English; colour analysis in Commonwealth English), also known as personal color analysis (PCA), seasonal color analysis, or skin-tone matching, is a term often used within the cosmetics and fashion industry to describe ...
*
Color in Chinese culture
Chinese culture attaches certain values to colors, like which colors are considered auspicious () or inauspicious (). The Chinese word for "color" is ''yánsè'' (). In Classical Chinese, the character ''sè'' () more accurately meant "color i ...
*
Color mapping
Color mapping is a function that maps (transforms) the colors of one (source) image to the colors of another (target) image. A color mapping may be referred to as the algorithm that results in the mapping function or the algorithm that transforms ...
*
Complementary color
*
Impossible color
Impossible colors are colors that do not appear in ordinary visual functioning. Different color theories suggest different hypothetical colors that humans are incapable of perceiving for one reason or another, and fictional colors are rou ...
*
International Color Consortium
*
International Commission on Illumination
*
Lists of colors (compact version)
*
Neutral color
Neutral or neutrality may refer to:
Mathematics and natural science Biology
* Neutral organisms, in ecology, those that obey the unified neutral theory of biodiversity
Chemistry and physics
* Neutralization (chemistry), a chemical reaction in ...
*
Pearlescent coating
Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterf ...
including Metal effect pigments
*
Pseudocolor
False color (or pseudo color) refers to a group of color Signal processing, rendering methods used to display images in color which were recorded in the visible spectrum, visible or non-visible parts of the electromagnetic spectrum. A false-c ...
*
Primary
Primary or primaries may refer to:
Arts, entertainment, and media Music Groups and labels
* Primary (band), from Australia
* Primary (musician), hip hop musician and record producer from South Korea
* Primary Music, Israeli record label
Works
* ...
,
secondary
Secondary may refer to: Science and nature
* Secondary emission, of particles
** Secondary electrons, electrons generated as ionization products
* The secondary winding, or the electrical or electronic circuit connected to the secondary winding i ...
and
tertiary colors
References
External links
ColorLabMATLAB toolbox for color science computation and accurate color reproduction (by Jesus Malo and Maria Jose Luque, Universitat de Valencia). It includes CIE standard tristimulus colorimetry and transformations to a number of non-linear color appearance models (CIE Lab, CIE CAM, etc.).
Buenos Aires University
*
*
*
Robert Ridgway'
''A Nomenclature of Colors'' (1886)an
''Color Standards and Color Nomenclature'' (1912)€”text-searchable digital facsimiles at Linda Hall Library
*
Albert Henry Munsell'
''A Color Notation''(1907) at Project Gutenberg
AIC International Colour AssociationThe Effect of Color , OFF BOOKDocumentary produced by
Off Book
''Off Book'' is a web series on digital culture and art created for PBS by Kornhaber Brown, a Webby award-winning production studio that creates web series, videos, and motion graphics. The series has been viewed more than six million times, and ...
Study of the history of colors
{{Authority control
Image processing
Qualia
Vision