A
set
Set, The Set, SET or SETS may refer to:
Science, technology, and mathematics Mathematics
*Set (mathematics), a collection of elements
*Category of sets, the category whose objects and morphisms are sets and total functions, respectively
Electro ...
of primary colors or primary colours (see
spelling differences) consists of
colorants or colored
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...
s that can be mixed in varying amounts to produce a
gamut of
colors. This is the essential method used to create the perception of a broad range of colors in, e.g., electronic displays, color printing, and paintings. Perceptions associated with a given combination of primary colors can be predicted by an appropriate mixing model (e.g.,
additive,
subtractive) that reflects the physics of how light interacts with physical media, and ultimately the
retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...
.
Primary colors can also be conceptual (not necessarily real), either as additive mathematical elements of a
color space or as irreducible phenomenological categories in domains such as psychology and
philosophy
Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. ...
. Color space primaries are precisely defined and empirically rooted in
psychophysical colorimetry experiments which are foundational for understanding
color vision. Primaries of some color spaces are ''complete'' (that is, all visible colors are described in terms of their primaries weighted by nonnegative primary intensity coefficients) but necessarily ''imaginary''
[Bruce MacEvoy. "Do 'Primary' Colors Exist?"]
imaginary or imperfect primaries section
). ''Handprint''. Accessed 10 August 2007. (that is, there is no plausible way that those primary colors could be represented physically, or perceived). Phenomenological accounts of primary colors, such as the psychological primaries, have been used as the conceptual basis for practical color applications even though they are not a quantitative description in and of themselves.
Sets of color space primaries are generally ''arbitrary'', in the sense that there is no one set of primaries that can be considered the canonical set. Primary pigments or light sources are selected for a given application on the basis of subjective preferences as well as practical factors such as cost, stability, availability etc.
The concept of primary colors has a long, complex history. The choice of primary colors has changed over time in different domains that study color. Descriptions of primary colors come from areas including philosophy, art history, color order systems, and scientific work involving the physics of light and perception of color.
Art education materials commonly use red, yellow, and blue as primary colors, sometimes suggesting that they can mix all colors. No set of real colorants or lights can mix all possible colors, however. In physics, the three primary colors are typically red, green and blue, after the different types of
photoreceptor pigments in the
cone cells.
Additive mixing of light
The perception elicited by multiple light sources co-stimulating the same area of the retina is
additive, i.e., predicted via summing the
spectral power distributions (the intensity of each wavelength) of the individual light sources assuming a color matching context.
For example, a
purple
Purple is any of a variety of colors with hue between red and blue. In the RGB color model used in computer and television screens, purples are produced by mixing red and blue light. In the RYB color model historically used by painters ...
spotlight on a dark background could be matched with coincident
blue and
red spotlights that are both dimmer than the purple spotlight. If the intensity of the purple spotlight was doubled it could be matched by doubling the intensities of both the red and blue spotlights that matched the original purple. The principles of additive color mixing are embodied in
Grassmann's laws. Additive mixing is sometimes described as "additive color matching" to emphasize the fact the predictions based on additivity only apply assuming the color matching context. Additivity relies on assumptions of the color matching context such as the match being in the
foveal
The fovea centralis is a small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina.
The fovea is responsible for sharp central vision (also called foveal vision), which is nece ...
field of view, under appropriate luminance, etc.
Additive mixing of coincident spot lights was applied in the experiments used to derive the
CIE 1931 colorspace (see
color space primaries section). The original ''
monochromatic'' primaries of the wavelengths of 435.8 nm (
violet), 546.1 nm (
green
Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a combin ...
), and 700 nm (red) were used in this application due to the convenience they afforded to the experimental work.
Small red, green, and blue elements (with controllable brightness) in electronic displays mix additively from an appropriate viewing distance to synthesize compelling colored images. This specific type of additive mixing is described as ''partitive mixing''.
Red, green, and blue light are popular primaries for partitive mixing since primary lights with those hues provide a large triangular chromaticity gamut.
The exact colors chosen for additive primaries are a compromise between the available technology (including considerations such as cost and power usage) and the need for large chromaticity gamut. For example, in 1953 the
NTSC specified primaries that were representative of the
phosphors available in that era for color
CRTs. Over decades, market pressures for brighter colors resulted in CRTs using primaries that deviated significantly from the original standard. Currently,
ITU-R BT.709-5 primaries are typical for
high-definition television
High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the g ...
.
Subtractive mixing of ink layers
The
subtractive color mixing model predicts the resultant spectral power distribution of light filtered through overlaid partially absorbing materials, usually in the context of an underlying reflective surface such as white paper.
Each layer partially absorbs some wavelengths of light from the illumination while letting others pass through, resulting in a colored appearance. The resultant spectral power distribution is predicted by the wavelength-by-wavelength product of the spectral reflectance of the illumination and the product of the spectral reflectances of all of the layers. Overlapping layers of ink in printing mix subtractively over reflecting white paper, while the reflected light mixes in a partitive way to generate color images.
Importantly, unlike additive mixture, the color of the mixture is not well predicted by the colors of the individual dyes or inks. The typical number of inks in such a printing process is 3 (CMY) or 4 (
CMYK), but can commonly range to 6 (e.g.,
Pantone hexachrome). In general, using fewer inks as primaries results in more economical printing but using more may result in better color reproduction.
Cyan (C),
magenta (M), and
yellow (Y) are good chromatic subtractive primaries in that filters with those colors can be overlaid to yield a surprisingly large chromaticity gamut. A black (K) ink (from the older "
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. The key plate, which is usually impressed using ...
") is also used in CMYK systems to augment C, M and Y inks or dyes due to both being more efficient in terms of time and expense and less likely to introduce visible defects. Before the color names ''cyan'' and ''magenta'' were in common use, these primaries were often known as blue and red, respectively, and their exact color has changed over time with access to new pigments and technologies. Organizations such as
Fogra,
European Color Initiative and
SWOP publish
colorimetric
Colorimetry is "the science and technology used to quantify and describe physically the human color perception".
It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color ...
CMYK standards for the printing industry.
Traditional red, yellow, and blue primary colors
Color theorists since the seventeenth century, and many artists and designers since that time, have taken red, yellow, and blue to be the primary colors (see
history below). This RYB system, in "traditional color theory", is often used to order and compare colors, and sometimes proposed as a system of mixing pigments to get a wide range of, or "all", colors.
[
O'Connor, Zena. "Traditional colour theory: A review." Color Research & Application, 8 January 2021.
]
O'Connor describes the role of RYB primaries in traditional color theory:
Traditional color theory is based on experience with pigments, more than on the science of light. In 1920, Snow and Froehlich explained: "It does not matter to the makers of dyes if, as the physicist says, red light and green light in mixture make yellow light, when they find by experiment that red pigment and green pigment in mixture produce gray. No matter what the spectroscope may demonstrate regarding the combination of yellow rays of light and blue rays of light, the fact remains that yellow pigment mixed with the blue pigment produces green pigment."
The widespread adoption of teaching of RYB as primary colors in post-secondary art schools in the twentieth century has been attributed to the influence of the
Bauhaus
The Staatliches Bauhaus (), commonly known as the Bauhaus (), was a German art school operational from 1919 to 1933 that combined crafts and the fine arts.Oxford Dictionary of Art and Artists (Oxford: Oxford University Press, 4th edn., 20 ...
, where
Johannes Itten
Johannes Itten (11 November 1888 – 25 March 1967) was a Swiss expressionist painter, designer, teacher, writer and theorist associated with the Bauhaus (''Staatliches Bauhaus'') school. Together with German-American painter Lyonel Feinin ...
developed his ideas on color during his time there in the 1920s, and of his book on color published in 1961.
[
]
In discussing color design for the web, Jason Beaird writes: "The reason many digital artists still keep a red, yellow, and blue color wheel handy is because the color schemes and concepts of traditional color theory are based on that model. ... Even though I design mostly for the Web—a medium that's displayed in RGB—I still use red, yellow, and blue as the basis for my color selection. I believe that color combinations created using the red, yellow, and blue color wheel are more aesthetically pleasing, and that good design is about aesthetics."
Of course, the notion that ''all'' colors can be mixed from RYB primaries is not true, just as it is not true in any system of real primaries.
For example, if the blue pigment is a deep
Prussian blue, then a muddy desaturated green may be the best that can be had by mixing with yellow.
[ To achieve a larger gamut of colors via mixing, the blue and red pigments used in illustrative materials such as the ''Color Mixing Guide'' in the image are often closer to peacock blue (a blue-green or cyan) and carmine (or crimson or magenta) respectively.][
][
][
]
Printers traditionally used inks of such colors, known as "process blue" and "process red", before modern color science and the printing industry converged on the process colors (and names) cyan and magenta[
(this is not to say that RYB is the same as CMY, or that it is exactly subtractive, but that there is a range of ways to conceptualize traditional RYB as a subtractive system in the framework of modern color science).
]
Mixing pigments in limited palettes
The first known use of red, yellow, and blue as "simple" or "primary" colors, by Chalcidius, ca. AD 300, was possibly based on the art of paint mixing.
Mixing pigments for the purpose of creating realistic paintings with diverse color gamuts is known to have been practiced at least since Ancient Greece
Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cu ...
(see history section). The identity of a/the set of minimal pigments to mix diverse gamuts has long been the subject of speculation by theorists whose claims have changed over time, for example, Pliny's white, black, one or another red, and "sil", which might have been yellow or blue; Robert Boyle's white, black, red, yellow, and blue; and variations with more or fewer "primary" color or pigments. Some writers and artists have found these schemes difficult to reconcile with the actual practice of painting. Nonetheless, it has long been known that limited palettes consisting of a small set of pigments are sufficient to mix a diverse gamut of colors.
The set of pigments available to mix diverse gamuts of color (in various media such as oil, watercolor, acrylic
Acrylic may refer to:
Chemicals and materials
* Acrylic acid, the simplest acrylic compound
* Acrylate polymer, a group of polymers (plastics) noted for transparency and elasticity
* Acrylic resin, a group of related thermoplastic or thermosett ...
, gouache
Gouache (; ), body color, or opaque watercolor is a water-medium paint consisting of natural pigment, water, a binding agent (usually gum arabic or dextrin), and sometimes additional inert material. Gouache is designed to be opaque. Gouache ...
, and pastel) is large and has changed throughout history. There is no consensus on a specific set of pigments that are considered primary colors the choice of pigments depends entirely on the artist's subjective preference of subject and style of art, as well as material considerations like lightfastness
Lightfastness is a property of a colourant such as dye or pigment that describes its resistance to fading when exposed to light. Dyes and pigments are used for example for dyeing of fabrics, plastics or other materials and manufacturing paints o ...
and mixing behavior. A variety of limited palettes have been employed by artists for their work.
The color of light (i.e., the spectral power distribution) reflected from illuminated surfaces coated in paint mixes is not well approximated by a subtractive or additive mixing model. Color predictions that incorporate light scattering effects of pigment particles and paint layer thickness require approaches based on the Kubelka–Munk equations, but even such approaches are not expected to predict the color of paint mixtures precisely due to inherent limitations. Artists typically rely on mixing experience and "recipes" to mix desired colors from a small initial set of primaries and do not use mathematical modeling.
MacEvoy explains why artists often chose a palette closer to RYB than to CMY: "Because the 'optimal' pigments in practice produce unsatisfactory mixtures; because the alternative selections are less granulating, more transparent, and mix darker values; and because visual preferences have demanded relatively saturated yellow to red mixtures, obtained at the expense of relatively dull green and purple mixtures. Artists jettisoned 'theory' to obtain the best color mixtures in practice."
Color space primaries
Color space primaries are derived from canonical colorimetric experiments that represent a standardized model of an observer (i.e., a set of ''color matching functions'') adopted by Commission Internationale de l'Eclairage (CIE) standards. The abbreviated account of color space primaries in this section is based on descriptions in ''Colorimetry - Understanding The CIE System''.
The CIE 1931 standard observer is derived experiments in which participants observing a foveal 2° bipartite field with a dark surround. Half of the field is illuminated with a monochromatic ''test stimulus'' (ranging from 380 nm to 780 nm) and the other half is the ''matching stimulus'' illuminated with three coincident monochromatic primary lights: 700 nm for red (R), 546.1 nm for green (G), and 435.8 nm for blue (B). These primaries correspond to CIE RGB color space. The intensities of the primary lights could be adjusted by the participant observer until the matching stimulus matched the test stimulus, as predicted by Grassman's laws of additive mixing. Different standard observers from other color matching experiments have been derived since 1931. The variations in experiments include choices of primary lights, field of view, number of participants etc. but the presentation below is representative of those results.
Matching was performed across many participants in incremental steps along the range of test stimulus wavelengths (380 nm to 780 nm) to ultimately yield the color matching functions: , and that represent the relative intensities of red, green, and blue light to match each wavelength (). These functions imply that