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For a set of ''subtractive'' primary colors for humans, as in mixing of pigments or dyes for printing, [[cyan]] (a bright aqua), [[magenta]] (fuchsia), and [[yellow]] are often used (usually supplemented by [[black]] to make [[CMYK color model|CMYK]]).<ref>{{cite book |title=Color and Its Applications |author=Matthew Luckiesh |year=1915 |publisher=D. Van Nostrand company |pages=58, 221 |url=https://books.google.com/books?id=0BgCAAAAYAAJ&pg=RA1-PA221&dq=magenta+cyan+yellow+date:0-1923+printing }}</ref> Although red, yellow, and blue ([[RYB_color_model|RYB]]) are a well-known traditional set of primaries, cyan and magenta can be mixed to produce blue, while yellow and magenta can be mixed to produce red, and therefore CMY[K] can produce most of the colors that RYB can, whereas typical RYB primaries cannot be mixed so as to produce intense shades similar to turquoise, magenta, and some green and orange shades for example.
For a set of ''subtractive'' primary colors for humans, as in mixing of pigments or dyes for printing, [[cyan]] (a bright aqua), [[magenta]] (fuchsia), and [[yellow]] are often used (usually supplemented by [[black]] to make [[CMYK color model|CMYK]]).<ref>{{cite book |title=Color and Its Applications |author=Matthew Luckiesh |year=1915 |publisher=D. Van Nostrand company |pages=58, 221 |url=https://books.google.com/books?id=0BgCAAAAYAAJ&pg=RA1-PA221&dq=magenta+cyan+yellow+date:0-1923+printing }}</ref> Although red, yellow, and blue ([[RYB_color_model|RYB]]) are a well-known traditional set of primaries, cyan and magenta can be mixed to produce blue, while yellow and magenta can be mixed to produce red, and therefore CMY[K] can produce most of the colors that RYB can, whereas typical RYB primaries cannot be mixed so as to produce intense shades similar to turquoise, magenta, and some green and orange shades for example.


The precise set of primary colors that are used in a specific color application depend on gamut requirements as well as application-specific constraints such as cost, power consumption, lightfastness, mixing behavior etc.
The precise set of primary colors to be used in a specific color application depends on gamut requirements as well as application-specific constraints such as cost, power consumption, lightfastness, mixing behavior etc.


== Additive and subtractive color mixing ==
== Additive and subtractive color mixing ==

Revision as of 23:58, 19 September 2017

File:CRT phosphors en.svg
The emission spectra of the three phosphors that define the additive primary colors of a CRT color video display. Other electronic color display technologies (LCD, Plasma display, OLED) have analogous sets of primaries with different emission spectra.

A set of primary colors is a set of pigments/dyes, colored lights, or abstract elements of a mathematical colorspace model (usually based on measured aspects of vision), that can be combined in certain ways to produce some gamut (range) of colors that are visible to humans or other animals, and sometimes some colors that aren't. Distinct colors can be specified in terms of a mixture of primary colors, facilitating technological and artistic applications such as painting, electronic displays and printing. Any small set of pigments or lights are "imperfect" physical primary colors in that they cannot be mixed to yield all possible colors that can be perceived by the color vision system, but some sets of primaries can produce a far wider range than others.

For an additive set of primary colors for human vision, as in a television or computer display screen, projector, or other emissive electronic visual displays, the usual choice is red, green, and blue (RGB), although the primaries' specific chromaticities can vary.

For a set of subtractive primary colors for humans, as in mixing of pigments or dyes for printing, cyan (a bright aqua), magenta (fuchsia), and yellow are often used (usually supplemented by black to make CMYK).[1] Although red, yellow, and blue (RYB) are a well-known traditional set of primaries, cyan and magenta can be mixed to produce blue, while yellow and magenta can be mixed to produce red, and therefore CMY[K] can produce most of the colors that RYB can, whereas typical RYB primaries cannot be mixed so as to produce intense shades similar to turquoise, magenta, and some green and orange shades for example.

The precise set of primary colors to be used in a specific color application depends on gamut requirements as well as application-specific constraints such as cost, power consumption, lightfastness, mixing behavior etc.

Additive and subtractive color mixing

In additive color mixing, the total light present is simply the sum of individual light sources. For example, an overlapping blue and red spotlight (on a white surface) produces a saturated purplish-pink such as magenta, which will be brighter than either of the spotlights alone. Combining two additive primaries produces a color brighter than either. For example, red and green lights together produce a yellow (if bright enough) or brown, while blue and green produce a bright, saturated greenish-blue or aqua such as cyan.

When paints, inks, or dyes are mixed or applied to a surface, each one absorbs certain proportions of the illuminating light at certain wavelengths. The result after each primary absorbs some of the light is therefore darker than any one of the primaries, i.e. they are said to mix subtractively.

Good additive primaries are often darker than their related subtractive counterparts (for example at least blue darker than cyan and magenta, red darker than magenta and yellow, and green darker than cyan and yellow), because they will be able to produce brighter colors (including the subtractive primaries themselves) when they sum. If subtractive primaries were that dark, they would not be able to produce such bright colors, except by allowing more of an illuminating light or white surface to show through and thus losing saturation as the color becomes more pastel.

A chromaticity diagram can illustrate the gamut (at a fixed luminance) of different choices of primaries, for example showing which colors are lost (and gained) if you use RGB for subtractive color mixing (instead of CMY).[2]

Biological basis

Population weighted cone spectral sensitivities

The effects of different primary colors are not merely due to fundamental properties of light, but rather are determined by the color vision system of a given type of animal. The human eye normally contains only three types of color photoreceptors (L, M and S) that are associated with specialized cone cells. These photoreceptor types respond to different (though overlapping) ranges of the visible electromagnetic spectrum, and there is no single wavelength that stimulates only one photoreceptor type. Humans and other species with three such types of color photoreceptor are known as trichromats.

Although there are complexities to the psychological process by which it is perceived, color has nevertheless been comprehensively mapped via controlled color matching experiments (e.g., CIE 1931), demonstrating the range of all possible colors visible to the average human eye in terms of each of the three color photoreceptors' responses and their corresponding three primaries called tristimulus values X, Y, and Z, which can be mathematically summed to specify essentially all colors that can be perceived (and some imaginary colors too). However, XYZ are termed abstract primaries in that some values of them cannot be physically realized by any combination of actual light due to the underlying structure and overlapping spectral sensitivities of each of the human cone photoreceptors.[3] Color appearance models like CIECAM02 describe color more generally in six dimensions and can be used to predict how colors appear under different viewing conditions.

For real (dye/pigment/light source) primary colors (as opposed to abstract like XYZ), the number of color receptors becomes the minimum number of primaries needed in order to produce more than a tiny sliver of the perceptible color gamut. Thus for trichromats like humans, we use three (or more) primaries for most general purposes. Two primaries would be unable to produce even some of the most common among the named colors. Adding a reasonable choice of third primary can drastically increase the available gamut, while adding a fourth or fifth may increase the gamut but typically not by as much.

Most placental mammals other than primates have only two types of color photoreceptor and are therefore dichromats, so it is possible that certain combinations of just two primaries might cover some significant gamut relative to the range of their color perception. Meanwhile, birds and marsupials have four color photoreceptors in their eyes, and hence are tetrachromats with a more complex colour perception system. There is no currently peer reviewed scholarly work that has confirmed the existence of a functional human tetrachromat, but they are suspected to exist.[4]

The presence of photoreceptor cell types in an organism's eyes do not directly imply that they are being used to functionally perceive color. Demonstrating improved spectral discrimination in any animal is difficult due to the underlying neural complexity of the process.[5]

History

There are numerous competing primary colour systems throughout history. Scholars and scientists engaged in debate over which hues best describe the primary color sensations of the eye.[6] Thomas Young proposed red, green and violet as the three primary colors, while James Clerk Maxwell favoured changing violet to blue. Hermann von Helmholtz proposed "a slightly purplish red, a vegetation-green, slightly yellowish, and an ultramarine-blue" as a trio.[7] In modern understanding, human cone cells do not correspond precisely to a specific set of primary colors, as each cone type responds to a relatively broad range of wavelengths.

Examples

Self portrait by Andres Zorn with white, red, yellow and black palette
A self portrait by Anders Zorn clearly showing a four pigment palette of what are thought to be white, yellow ochre, red vermilion and black pigments.[8]
LCD pixels
A photograph of the red, green and blue pixels of an LC display.
CMYK inks
The cyan, magenta, yellow and black (key) (CMYK) inks found in an inkjet printer that can be used for color photographic reproduction.

Limited palettes in visual art

There are hundreds of commercially available pigments for visual artists to use and mix (in various media such as oil, watercolor, acrylic and pastel). A common approach is to use just a limited palette of pigments (often between four and eight) that can be physically mixed to any color that the artist desires in the final work. There are no specific set of pigments that are primary colors, the choice of pigment depends entirely on the artist's subjective preference of subject and style of art as well as material considerations like lightfastness and mixing heuristics. Contemporary classical realists have often advocated that a limited palette of white, red, yellow and black pigment (often described as the "Zorn palette") is sufficient for compelling work.[9]

RGB for electronic displays

Three Laser diodes showing the RGB colours, those being red, blue and green

Media that combine emitted lights to create the sensation of a range of colors are using the additive color system. The primary colors used in most electronic displays are typically saturated red, green and blue light.[10]

The exact colors chosen for the primaries are a technological compromise between the available phosphors (including considerations such as cost and power usage) and the need for large color triangle to allow a large gamut of colors. The ITU-R BT.709-5/sRGB primaries are typical. Additive mixing of red and green light produces shades of yellow, orange, or brown.[11] Mixing green and blue produces shades of cyan, and mixing red and blue produces shades of purple, including magenta. Mixing nominally equal proportions of the additive primaries results in shades of grey or white; the color space that is generated is called an RGB color space. The experiments used to derive the CIE 1931 colorspace used monochromatic primary colored lights with the (arbitrary) wavelengths of 435.8 nm (violet), 546.1 nm (green) and 700 nm (red) due to the convenience they afforded to the experimental work.

Recent developments

Some recent TV and computer displays are starting to include yellow as a fourth primary color, often in a four-point square pixel area, so as to achieve brighter pure yellows and a larger color gamut.[12] Even the four-primary technology does not yet reach the range of colors that the human eye can see from light reflected by illuminated surfaces (as defined by the sample-based estimate called the Pointer Gamut[13]), with 4-primary LED prototypes providing typically about 87% and 5-primary prototypes about 95%. Several firms, including Samsung and Mitsubishi, have demonstrated LED displays with five or six "primaries", or color LED point light sources per pixel.[14][15] A recent academic literature review claims a gamut of 99% can be achieved with 5-primary LED technology.[16] While technology for achieving a wider gamut appears to be within reach, other issues remain; for example, affordability, dynamic range, and brilliance. In addition, there exists hardly any source material recorded in this wider gamut, nor is it currently possible to recover this information from existing visual media. Regardless, industry is still exploring a wide variety of "primary" active light sources (per pixel) with the goal of matching the capability of human color perception within a broadly affordable price. One example of a potentially affordable but yet unproven active light hybrid places an LED screen over a plasma light screen, each with different "primaries".

CMYK color model or four-color printing

In the printing industry, the subtractive primaries cyan, magenta and yellow are applied together in varying amounts for useful gamuts. An additional key ink (shorthand for the key printing plate that impressed the artistic detail of an image, usually in black ink.[17]) is also usually used since it is difficult to mix a dark enough black ink using the other three inks as well as other practical considerations such as cost and ink bleed. Before the color names cyan and magenta were in common use, these primaries were often known as blue-green and purple or in some pop art circles as blue and red, respectively, and their exact color has changed over time with access to new pigments and technologies.[18]

Psychological primaries

Approximations within the sRGB gamut to the "aim colors" of the Natural Color System, a model based on the opponent process theory of color vision.

The 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. The three types of cones have some overlap in the wavelengths of light 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 versus green, blue versus yellow and black versus white.[19] Responses to one color of an opponent channel are antagonistic to those of the other color. The theory states that 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 could be described in terms of some combination of these.

See also

References

  1. ^ Matthew Luckiesh (1915). Color and Its Applications. D. Van Nostrand company. pp. 58, 221.
  2. ^ Steven Westland, "subtractive mixing – why not RGB?", October 4, 2009 http://colourware.org/2009/10/04/subtractive-mixing-why-not-rgb/
  3. ^ Bruce MacEvoy. "Do 'Primary' Colors Exist?" (Material Trichromacy section). Handprint. Accessed 10 August 2007.
  4. ^ Greenwood, Veronique. "The Humans With Super Human Vision". Discover Magazine. Kalmbach Publishing Co. Retrieved 29 September 2016.
  5. ^ Morrison, Jessica (23 January 2014). "Mantis shrimp's super colour vision debunked". Nature. doi:10.1038/nature.2014.14578.
  6. ^ Edward Albert Sharpey-Schäfer (1900). Text-book of physiology. Vol. 2. Y. J. Pentland. p. 1107.
  7. ^ Alfred Daniell (1904). A text book of the principles of physics. Macmillan and Co. p. 575.
  8. ^ Nyholm, Arvid (1914). "Anders Zorn: The Artist and the Man". Fine Arts Journal. 31 (4): 469. doi:10.2307/25587278.
  9. ^ Gurney. "The Zorn Palette". Gurney Journey. Retrieved 27 September 2016.
  10. ^ Thomas D. Rossing; Christopher J. Chiaverina (1999). Light science: physics and the visual arts. Birkhäuser. p. 178. ISBN 978-0-387-98827-6. {{cite book}}: Unknown parameter |lastauthoramp= ignored (|name-list-style= suggested) (help)
  11. ^ "Some Experiments on Color", Nature 111, 1871, in John William Strutt (Lord Rayleigh) (1899). Scientific Papers. University Press.
  12. ^ Garvey, Jude (2010-01-20). "Sharp four primary color TVs enable over one trillion colors". gizmag.com.
  13. ^ M. R. Pointer (1980). "The Gamut of Real Surface Colours". Color Research and Application. 5 (3). John Wiley & Sons, Inc.: 145–155. doi:10.1002/col.5080050308.
  14. ^ Chih-Cheng Chan; Guo-Feng Wei; Hui Chu-Ke; Sheng-Wen Cheng; Shih-Chang Chu; Ming-Sheng Lai; Arex Wang; Shmuel Roth; Oded Ben David; Moshe Ben Chorin; Dan Eliav; Ilan Ben David (1999). Development of Multi-Primary Color LCD. AU Optronics, Science-Based Industrial Park, Hsin-Chu, Taiwan; Genoa Color Technologies, Herzelia, Israel.
  15. ^ Thomas Rossing; Christopher J Chiaverina (24 September 1999). Light Science: Physics and the Visual Arts. Springer Science & Business Media. pp. 178–. ISBN 978-0-387-98827-6.
  16. ^ Abhinav Priya (2011), Five-Primary Color LCD (PDF), Cochin University of Science and Technology, Department of Electronics Engineering, p. 2
  17. ^ Frank S. Henry (1917). Printing for School and Shop: A Textbook for Printers' Apprentices, Continuation Classes, and for General use in Schools. John Wiley & Sons.
  18. ^ Ervin Sidney Ferry (1921). General Physics and Its Application to Industry and Everyday Life. John Wiley & Sons.
  19. ^ Michael Foster (1891). A Text-book of physiology. Lea Bros. & Co. p. 921.