Primary color - AbsoluteAstronomy.com

Primary colors are sets of colors that can be combined to make a useful range of colors. For human applications, three primary colors are usually used, since human color vision

Color vision

Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths of the light they reflect, emit, or transmit...

is trichromatic.

For additive combination of colors, as in overlapping projected lights or in CRT

Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

displays, the primary colors normally used are red

Red

Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...

, green

Green

Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...

, and blue

Blue

Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...

. For subtractive combination of colors, as in mixing of pigment

Pigment

A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

s or dye

Dye

A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....

s, such as in printing, the primaries normally used are cyan

Cyan

Cyan from , transliterated: kýanos, meaning "dark blue substance") may be used as the name of any of a number of colors in the blue/green range of the spectrum. In reference to the visible spectrum cyan is used to refer to the color obtained by mixing equal amounts of green and blue light or the...

, magenta

Magenta

Magenta is a color evoked by light stronger in blue and red wavelengths than in yellowish-green wavelengths . In light experiments, magenta can be produced by removing the lime-green wavelengths from white light...

, and yellow

Yellow

Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, with no significant stimulation of the S cone cells. Light with a wavelength of 570–590 nm is yellow, as is light with a suitable mixture of red and green...

, though the set of red

Red

, yellow

Yellow

, blue

Blue

is popular among artists.
See RGB color model

RGB color model

The RGB color model is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors...

, CMYK color model

CMYK color model

The CMYK color model is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key...

, and RYB color model

RYB color model

RYB is a historical set of colors used in subtractive color mixing, and is one commonly used set of primary colors...

for more on these popular sets of primary colors.

Any choice of primary colors is essentially arbitrary; for example, an early color photographic process, autochrome

Autochrome Lumière

The Autochrome Lumière is an early color photography process. Patented in 1903 by the Lumière brothers in France and first marketed in 1907, it was the principal color photography process in use before the advent of subtractive color film in the mid-1930s....

, typically used orange, green

Green

, and violet

Violet (color)

As the name of a color, violet is synonymous with a bluish purple, when the word "purple" is used in the common English language sense of any color between blue and red, not including either blue or red...

primaries. However, unless negative amounts of a color are allowed the gamut

Gamut

In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a...

will be restricted by the choice of primaries.

The combination of any two primary colors creates a secondary color.

The most commonly used additive color

Additive color

An additive color model involves light emitted directly from a source or illuminant of some sort. The additive reproduction process usually uses red, green and blue light to produce the other colors. Combining one of these additive primary colors with another in equal amounts produces the...

primaries are the secondary color

Secondary color

A secondary color is a color made by mixing two primary colors in a given color space. Examples include the following:-Light : red + green = yellowgreen + blue = cyan blue +...

s of the most commonly used subtractive color

Subtractive color

A subtractive color model explains the mixing of paints, dyes, inks, and natural colorants to create a full range of colors, each caused by subtracting some wavelengths of light and reflecting the others...

primaries, and vice versa.

Biological basis

Primary colors are not a fundamental property of light but are often related to the physiological response of the eye to light. Fundamentally, light is a continuous spectrum

Spectrum

A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

of the wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

s that can be detected by the human eye, an infinite-dimensional stimulus

Stimulus (physiology)

In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....

space. However, the human eye normally contains only three types of color receptors, called cone cell

Cone cell

Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...

s. Each color receptor responds to different ranges of the color spectrum. Humans and other species with three such types of color receptors are known as trichromats. These species respond to the light stimulus via a three-dimensional sensation, which generally can be modeled as a mixture of three primary colors.

Before the nature of colorimetry and visual physiology were well understood, scientists such as Thomas Young

Thomas Young (scientist)

Thomas Young was an English polymath. He is famous for having partly deciphered Egyptian hieroglyphics before Jean-François Champollion eventually expanded on his work...

, James Clark Maxwell, and Hermann von Helmholtz

Hermann von Helmholtz

Hermann Ludwig Ferdinand von Helmholtz was a German physician and physicist who made significant contributions to several widely varied areas of modern science...

expressed various opinions about what should be the three primary colors to describe the three primary color sensations of the eye. Young originally proposed red, green, and violet, and Maxwell changed violet to blue; Helmholtz proposed "a slightly purplish red, a vegetation-green, slightly yellowish (wave-length about 5600 tenth-metres), and an ultramarine-blue (about 4820)". In modern understanding, the human cone cell

Cone cell

s do not correspond to any real primary colors.

Species with different numbers of receptor cell types would have color vision requiring a different number of primaries. For example, for species known as tetrachromats, with four different color receptors, one would use four primary colors. Since humans can only see to 380 nanometers (violet

Violet (color)

), but tetrachromats can see into the ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

to about 300 nanometers, this fourth primary color for tetrachromats is located in the shorter-wavelength range.

Many bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s and marsupial

Marsupial

Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...

s are tetrachromats, and it has been suggested that some human females are tetrachromats as well, having an extra variant version of the long-wave (L) cone type.
The peak response of human color receptors varies, even among individuals with "normal" color vision; in non-human species this polymorphic variation is even greater, and it may well be adaptive.
Most mammals other than primates have only two types of color receptors and are therefore dichromats; to them, there are only two primary colors.

It would be incorrect to assume that the world "looks tinted" to an animal (or human) with anything other than the human standard of three color receptors. To an animal (or human) born that way, the world would look normal to it, but the animal's ability to detect and discriminate colors would be different from that of a human with normal color vision. If a human and an animal both look at a natural color, they see it as natural; however, if both look at a color reproduced via primary colors, such as on a color television

Color television

Color television is part of the history of television, the technology of television and practices associated with television's transmission of moving images in color video....

screen, the human may see it as matching the natural color, while the animal does not, since the primary colors have been chosen to suit human capabilities.

Additive primaries

Media that combine emitted lights to create the sensation of a range of colors are using the additive color

Additive color

system. Typically, the primary colors used are red, green, and blue.

Television

Television

Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

and other computer and video displays are a common example of the use of additive primaries and the RGB color model

RGB color model

The RGB color model is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors...

. The exact colors chosen for the primaries are a technological compromise between the available phosphor

Phosphor

A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...

s (including considerations such as cost and power usage) and the need for large color triangle

Color triangle

A color triangle is an arrangement of colors within a triangle, based on the additive combination of three primary colors at its corners.An additive color space defined by three primary colors has a chromaticity gamut that is a color triangle, when the amounts of the primaries are constrained to be...

to allow a large gamut of colors. The ITU-R BT.709-5

Rec. 709

ITU-R Recommendation BT.709, more commonly known by the abbreviations Rec. 709 or BT.709, standardizes the format of high-definition television, having 16:9 aspect ratio. The first edition of the standard was approved in 1990....

/sRGB primaries are typical.
Additive mixing of red and green light produces shades of yellow

Yellow

, orange, or brown

Brown

Brown is a color term, denoting a range of composite colors produced by a mixture of orange, red, rose, or yellow with black or gray. The term is from Old English brún, in origin for any dusky or dark shade of color....

. Mixing green and blue produces shades of cyan, and mixing red and blue produces shades of purple

Purple

Purple is a range of hues of color occurring between red and blue, and is classified as a secondary color as the colors are required to create the shade....

, including magenta

Magenta

. Mixing nominally equal proportions of the additive primaries results in shades of grey

Grey

Grey or gray is an achromatic or neutral color.Complementary colors are defined to mix to grey, either additively or subtractively, and many color models place complements opposite each other in a color wheel. To produce grey in RGB displays, the R, G, and B primary light sources are combined in...

or white

White

White is a color, the perception of which is evoked by light that stimulates all three types of color sensitive cone cells in the human eye in nearly equal amounts and with high brightness compared to the surroundings. A white visual stimulation will be void of hue and grayness.White light can be...

; the color space

Color space

A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components...

that is generated is called an RGB color space

RGB color space

An RGB color space is any additive color space based on the RGB color model. A particular RGB color space is defined by the three chromaticities of the red, green, and blue additive primaries, and can produce any chromaticity that is the triangle defined by those primary colors...

.

The CIE 1931 color space

CIE 1931 color space

In the study of color perception, one of the first mathematically defined color spaces is the CIE 1931 XYZ color space, created by the International Commission on Illumination in 1931....

defines monochromatic primary colors with wavelengths of 435.8 nm (violet), 546.1 nm (green) and 700 nm (red). The corners of the color triangle are therefore on the spectral locus, and the triangle is about as big as it can be. No real display device uses such primaries, as the extreme wavelengths used for violet and red result in a very low luminous efficiency.

Subtractive primaries

Media that use reflected light and colorants to produce colors are using the subtractive color

Subtractive color

method of color mixing.

Traditional

RYB (red, yellow, and blue) is a historical set of subtractive primary colors. It is primarily used in art and art education, particularly painting

Painting

Painting is the practice of applying paint, pigment, color or other medium to a surface . The application of the medium is commonly applied to the base with a brush but other objects can be used. In art, the term painting describes both the act and the result of the action. However, painting is...

. It predates modern scientific color theory

Color theory

In the visual arts, color theory is a body of practical guidance to color mixing and the visual impacts of specific color combinations. Although color theory principles first appeared in the writings of Leone Battista Alberti and the notebooks of Leonardo da Vinci , a tradition of "colory theory"...

RYB make up the primary colors in a painter's color wheel

Color wheel

A color wheel or color circle is an abstract illustrative organization of color hues around a circle that shows relationships between primary colors, secondary colors, complementary colors, etc....

; the secondary color

Secondary color

A secondary color is a color made by mixing two primary colors in a given color space. Examples include the following:-Light : red + green = yellowgreen + blue = cyan blue +...

s VOG (violet, orange, and green) make up another triad. Triads are formed by 3 equidistant colors on a particular color wheel; neither RYB nor VOG is equidistant on a perceptually uniform color wheel, but rather have been defined to be equidistant in the RYB wheel.

Painters have long used more than three "primary" colors in their palettes—and at one point considered red, yellow, blue, and green to be the four primaries. Red, yellow, blue, and green are still widely considered the four psychological primary colors, though red, yellow, and blue are sometimes listed as the three psychological primaries, with black and white occasionally added as a fourth and fifth.

During the 18th century, as theorists became aware of Isaac Newton

Isaac Newton

Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

’s scientific experiments with light and prisms, red, yellow, and blue became the canonical primary colors—supposedly the fundamental sensory qualities that are blended in the perception of all physical colors and equally in the physical mixture of pigments or dyes. This theory became dogma, despite abundant evidence that red, yellow, and blue primaries cannot mix all other colors, and has survived in color theory to the present day.

Using red, yellow, and blue as primaries yields a relatively small gamut

Gamut

, in which, among other problems, colorful greens, cyans, and magentas are impossible to mix, because red, yellow, and blue are not well-spaced around a perceptually uniform color wheel. For this reason, modern three- or four-color printing processes, as well as color photography, use cyan, yellow, and magenta as primaries instead. Most painters include colors in their palettes which cannot be mixed from yellow, red, and blue paints, and thus do not fit within the RYB color model. Some who do use a three-color palette opt for the more evenly spaced cyan, yellow, and magenta used by printers, and others paint with 6 or more colors to widen their gamuts. The cyan, magenta, and yellow used in printing are sometimes known as "process blue," "process red," and "process yellow."

CMYK color model, or four-color printing

In the printing industry, to produce the varying colors the subtractive primaries cyan

Cyan

, magenta

Magenta

, and yellow

Yellow

are applied together in varying amounts. Before the color names cyan and magenta were in common use, these primaries were often known as blue-green and purple, or in some circles as blue and red, respectively, and their exact color has changed over time with access to new pigments and technologies.

Mixing yellow and cyan produces green colors; mixing yellow with magenta produces reds, and mixing magenta with cyan produces blues. In theory, mixing equal amounts of all three pigments should produce grey, resulting in black when all three are applied in sufficient density, but in practice they tend to produce muddy brown

Brown

colors. For this reason, and to save ink and decrease drying times, a fourth pigment, black

Black

Black is the color of objects that do not emit or reflect light in any part of the visible spectrum; they absorb all such frequencies of light...

, is often used in addition to cyan, magenta, and yellow.

The resulting model is the so-called CMYK color model

CMYK color model

. The abbreviation

Abbreviation

An abbreviation is a shortened form of a word or phrase. Usually, but not always, it consists of a letter or group of letters taken from the word or phrase...

stands for cyan, magenta, yellow, and key—black is referred to as the key color, a shorthand for the key printing plate
Key plate
In printing, a key plate is the plate which prints the detail in an image.When printing color images by combining multiple colors of inks, the colored inks usually do not contain much image detail...

that impressed the artistic detail of an image, usually in black ink.

In practice, colorant mixtures in actual materials such as paint

Paint

Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...

tend to be more complex. Brighter or more saturated

Saturation (color theory)

In colorimetry and color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity of a specific color. Colorfulness is the degree of difference between a color and gray. Chroma is the colorfulness relative to the brightness of another color...

colors can be created using natural pigments instead of mixing, and natural properties of pigments can interfere with the mixing. For example, mixing magenta and green in acrylic

Acrylic paint

Acrylic paint is fast drying paint containing pigment suspension in acrylic polymer emulsion. Acrylic paints can be diluted with water, but become water-resistant when dry...

creates a dark cyan—something which would not happen if the mixing process were perfectly subtractive.

In the subtractive model, adding white to a color, whether by using less colorant or by mixing in a reflective white pigment such as zinc oxide

Zinc oxide

Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

, does not change the color’s hue

Hue

Hue is one of the main properties of a color, defined technically , as "the degree to which a stimulus can be describedas similar to or different from stimuli that are described as red, green, blue, and yellow,"...

but does reduce its saturation. Subtractive color printing works best when the surface or paper is white, or close to it.

A system of subtractive color does not have a simple chromaticity gamut analogous to the RGB color triangle, but a gamut that must be described in three dimensions. There are many ways to visualize such models, using various 2D chromaticity spaces or in 3D color spaces.

Psychological primaries

Main article: Opponent process
Opponent process
The color opponent process is a color theory that states that the human visual system interprets information about color by processing signals from cones and rods in an antagonistic manner...

. See also: Natural Color System
Natural Color System
The Natural Color System is a proprietary perceptual color model published by the Scandinavian Colour Institute of Stockholm, Sweden. It is based on the color opponency description of color vision, first proposed by German physiologist Ewald Hering...

, Unique hues
Unique hues
In the opponent process theory of color, there are four unique hues – red, yellow, green, and blue – relative to which other hues are defined. Unique red is a red which appears to have no yellow or blue in it; unique yellow is a yellow which appears to have no red or green in it; etc.Color names...

The opponent process

Opponent process

The color opponent process is a color theory that states that the human visual system interprets information about color by processing signals from cones and rods in an antagonistic manner...

is a color theory

Color theory

that states that the human visual system

Visual system

The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...

interprets information about color

Color

Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...

by processing signals from cones

Cone cell

and rods

Rod cell

Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...

in an antagonistic manner. The three types of cones have some overlap in the wavelengths of light

Light

Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

to which they respond, so it is more efficient for the visual system to record differences between the responses of cones, rather than each type of cone's individual response. The opponent color theory suggests that there are three opponent channels: red

Red

versus green

Green

, blue

Blue

versus yellow

Yellow

, and black

Black

Black is the color of objects that do not emit or reflect light in any part of the visible spectrum; they absorb all such frequencies of light...

versus white

White

. Responses to one color of an opponent channel are antagonistic to those of the other color. The particular colors considered by an observer to be uniquely representative of the concepts red, yellow, green, blue, white, and black might be called “psychological primary colors”, because any other color can be described in terms of some combination of these.

External links

Bruce MacEvoy. "Do Primary Colors Exist?". handprint.com. The history and science of primary colors, part of MacEvoy’s sprawling comprehensive site about color.
Ask A Scientist: Primary Colors
The Color-Sensitive Cones at HyperPhysics
Color Tutorial

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.