Editing Natural Color System

{{Short description|Proprietary perceptual color model}}

[[File:Animation of the NCS Colour System.gif|right|thumb|240px|Animation showing the NCS 1950 standard color samples in the NCS color circle and hue triangles.]]
[[File:Opponent colors.svg|right|thumb|240px|The NCS color model is based on the three pairs of elementary colors ([[white]]–[[black]], [[green]]–[[red]], and [[yellow]]–[[blue]]), as defined by [[color opponency]].]]
[[File:Flag of Sweden.svg|thumb|240px|The colors of the [[Flag of Sweden|Swedish flag]] are officially established to be NCS 0580-Y10R for the shade of yellow, and NCS 4055-R95B for the shade of blue]]

The '''Natural Colour System''' ('''NCS''') is a [[Patent|proprietary]] [[perception|perceptual]] [[color model]]. It is based on the [[opponent process|color opponency]] hypothesis of [[color vision]], first proposed by German physiologist [[Ewald Hering]].<ref>{{Cite book|title = Outlines of a Theory of the light sense|last = Hering|first = Ewald|publisher = Harvard University Press|year = 1964|location = Cambridge Mass.|editor-last = Hurvich|editor-first = L.M.|orig-year = 1878, Zur Lehre vom Lichtsinne, Wien|editor-last2 = Jameson|editor-first2 = D.}}</ref> The current version of the NCS was developed by the [[Swedish Colour Centre Foundation]], from 1964 onwards. The research team consisted of [[Anders Hård]], [[Lars Sivik]] and [[Gunnar Tonnquist]], who in 1997 received the [[International Colour Association|AIC]] Judd award for their work.<ref name=":0">{{Cite journal|title = NCS Natural Colour System - from Concepts to Research and Applications. Part I and II.|last1 = Hård|first1 = A.|date = 1996|journal = Color Research and Application|last2 = Sivik|first2 = L.|pages = 180–220|volume = 21|last3 = Tonnquist|first3 = G.|doi = 10.1002/(SICI)1520-6378(199606)21:3<180::AID-COL2>3.0.CO;2-O}}</ref><ref>{{Cite web|url = http://www.aic-colour.org/judd.htm|title = International Colour Association}}</ref> The system is based entirely on the [[Phenomenology (psychology)|phenomenology]] of human perception as opposed to [[color mixing]]. It is illustrated by a color atlas, marketed by NCS Colour AB in Stockholm.

== Definition ==
The NCS states that there are six elementary [[color]] percepts of human vision—which might coincide with the [[primary color#Psychological primaries|psychological primaries]]—as proposed by the hypothesis of [[color opponency]]: [[white]], [[black]], [[red]], [[yellow]], [[green]], and [[blue]]. The last four are also called [[unique hues]]. In the NCS all six are defined as elementary colors, irreducible [[qualia]], each of which would be impossible to define in terms of the other elementary colors. All other experienced colors are considered composite perceptions, i.e. experiences that can be defined in terms of similarity to the six elementary colors. E.g., a saturated [[pink]] would be fully defined by its visual similarity to red, blue, black and white.<ref name=":0" />

Colors in the NCS are defined by three values, expressed in [[percentage]]s, specifying the degree of blackness (''s'', = relative visual similarity to the black elementary color), [[Chromaticity|chromaticness]] (''c'', = relative visual similarity to the "strongest", most saturated, color in that hue triangle), and [[hue]] (''Φ'', = relative similarity to one or two of the chromatic elementary colors red, yellow, green and blue, expressed in at most two percentages). This means that a color can be expressed as either Y (yellow), YR (yellow with a red component), R (red), RB (red with a blue component), B (blue), etc. No hue is considered to have visual similarity to both hues of an opponent pair; i.e., there is no "redgreen" or "yellowblue". The blackness and the chromaticness together add up to less than or equal to 100%. The remainder from 100%, if any, gives the amount of whiteness (''w'').<ref name=":0" /> [[Achromatic colors]], i.e., colors that lack chromatic contents (ranging from black, to grey and finally white), have their hue component replaced with a capital "N"; for example, {{colorsample|#191919|description=sample of S9000N}} "NCS S 9000-N" (a more or less complete black). NCS color notations are sometimes prepended by a capital "S", which denotes that the current version of the NCS color standard was used to specify the color.

In summary, the NCS color notation for {{colorsample|#D38E87|description=sample of S2030Y90R}} '''S 2030-Y90R''' (light, pinkish red) is described as follows.

: <math>
\underset{\begin{matrix} \vphantom{|^|}\text{NCS 1950} \\[-4mu] \text{Standard} \end{matrix}} { \text{S} } \quad 
\underbrace{\underset{\vphantom{|^|}s}{20}\ \underset{\vphantom{|^|}c}{30}}_{\text{nuance}}
\quad\frac{\phantom{i}}{}\quad
\underbrace{\text{Y}\ \underset{\vphantom{|^|}\phi}{90}\ \text{R}}_{\text{hue}}
</math>

with

: <math>w = 100 - c - s = 100 - 30 - 20 = 50</math>

=== Saturation and lightness ===
In addition to the above values ''s'' (blackness), ''w'' (whiteness), ''c'' (chromaticness) and ''Φ'' (hue), the NCS system can also describe the two perceptual quantities [[Colorfulness#Saturation|saturation]] and lightness. NCS saturation (''m'') refers to a color's relation between its chromaticness and whiteness (regardless of hue), defined as the ratio between the chromaticness and the sum of its whiteness and chromaticness <math>m = c / (w + c) = c / (100 - s)</math>. The NCS saturation ranges between 0 and 1.

For the example color of '''S 2030-Y90R''', the saturation is calculated as 
: <math>m = c / (100 - s) = 30 / (100 - 20) = 30 / 80 = 0.375.</math>

NCS lightness (''v'') is a color's perceptual characteristic to contain more of the achromatic elementary colors black or white than another color. NCS lightness values varies from 0 for the elementary color black (S) to 1 for the elementary color white (W). For achromatic colors, that is any black, gray or white with no chromatic component (''c'' = 0), lightness is defined as 
: <math>v = \frac{100 - s}{100}.</math>

For chromatic colors, the NCS lightness is determined by comparing the chromatic color to a reference scale of achromatic colors (''c'' = 0), and is determined to have the same lightness value ''v'' as the sample on the reference scale to which it has the least noticeable edge-to-edge difference.

=== Examples ===
Two examples of NCS color notation&mdash;the yellow and blue shades of the [[Swedish flag]]:<ref>{{Cite web|url=https://lagen.nu/1983:826|title=Swedish legal regulation on flag colour|date=2016-03-29}}</ref>
* {{colorsample|#FFC300|description=sample of 0580Y10R}} Yellow – NCS 0580-Y10R (nuance = 5% blackness, 80% chromaticness, hue = 90% yellow + 10% red. Strong, very slightly blackish yellow with a slight orangish tinge)
* {{colorsample|#015483|description=sample of 4055R95B}} Blue – NCS 4055-R95B (nuance = 40% blackness, 55% chromaticness, hue = 5% red + 95% blue. Somewhat dark, medium strong blue with a very slight purplish tinge)
The NCS is represented in nineteen countries and is the reference norm for color designation in [[Sweden]] (since 1979), [[Norway]] (since 1984), [[Spain]] (since 1994) and [[South Africa]] (since 2004). It is also one of the standards used by the [[International Colour Authority]], a leading publisher of color trend forecasts for the [[interior design]] and textile markets.

== NCS 1950 Standard Colors ==

In order to be able to manufacture physical representations of the NCS color space (such as color atlases), a reduced set of colors had to be selected that would illustrate the system well. Originally developed in 1979 as part of becoming the Swedish national color standard by the SIS (Swedish Standards Institute), the Natural Color System was described in an atlas containing 1412 colors. In 1984, an additional 118 colors were added for a total of 1530 colors. Eleven years later, in 1995, a second edition of the NCS Color Samples was released containing 1750 standard colors. In 2004, 200 more colors (184 light colors and 16 in the blue-green space) were added, resulting in the NCS 1950 standard colors. Colors that have a representation in the NCS 1950 samples are denoted with a leading capital "S", for example {{colorsample|#F5B50B|description=Sample of 1070Y10R}} NCS S 1070-Y10R (a chromatic, slightly reddish yellow).

== Comparisons to other color systems ==
The most important difference between NCS and most other color systems resides in their starting points. The aim of NCS is to define colors from their visual appearance, as they are experienced by human consciousness. Other color models, such as [[CMYK color model|CMYK]] and [[RGB color model|RGB]], are based on an understanding of physical processes, how colors can be achieved or "made" in different media.<ref>{{Cite journal|title = The Value of Knowledge for Color Design|last = Green-Armytage|first = Paul|date = 2006|journal = Color Research and Application|volume = 31|issue = 31:4|pages = 253–269|doi = 10.1002/col.20222}}</ref>

According to the opponent process hypothesis, the underlying physiological mechanisms involved in color opponency include the [[bipolar cell|bipolar]] and [[Retinal ganglion cell|ganglion cell]]s in the [[retina]], which process the signal originated by the retinal [[cone cell|cones]] before it is sent to the [[brain]]. Models like [[RGB color model|RGB]] are based<!-- this is correct. XYZ (not RGB) _describes_ it --> on what happens at the lower, retinal cone level, and thus are fitted for presenting self-illuminated, dynamic images as done by [[Television set|TV sets]] and [[computer display]]s; see [[additive color]]. The NCS model, for its part, describes the organization of the color sensations as perceived at the upper, brain level, and thus is much better fitted than RGB to deal with how humans experience and describe their color sensations (hence the "natural" part of its name). More problematic is the relation with the CMYK-model which is generally seen as a correct prediction of the behavior of [[color mixing|mixing pigments]], as a system of [[subtractive color]]. The NCS coincides with the CMYK as regards the green-yellow-red segment of the [[color circle]], but differs from it in seeing the saturated subtractive [[primary color]]s [[magenta]] and [[cyan]] as complex sensations of a "redblue" and a "greenblue" respectively and in seeing green, not as a [[secondary color]] mix of yellow and cyan, but as a unique hue. The NCS explains this by assuming that the behavior of paint is partly counterintuitive to human phenomenology. Observing that the mix of yellow and "greenblue" (cyan) paint results in a green color, would thus be at odds with the intuition of human perception, because green would be perceived as an elementary hue while yellow and the presumed blue component of "greenblue" are by the NCS considered to be mutually excluding percepts.

Hering argued that yellow is not a "redgreen" but a unique hue. [[Colorimetry|Colorimetrist]] [[Jan Koenderink]], in a critique of Hering's system, considered it inconsistent not to apply the same argument to the other two subtractive primaries (or additive secondaries), cyan and magenta, and see them as unique hues as well, not a "greenblue" or a "redblue". He also pointed out the difficulty within a four-color theory that the primaries would not be equally spaced in the color circle; and the problem that Hering does not account for the fact that cyan and magenta are lighter than green, blue and red, whereas this is, in his view, elegantly explained within the CMYK-model. He concluded that Hering's scheme fitted common language better than color experience.<ref>[[Jan Koenderink|Jan J. Koenderink]], 2010, ''Color for the Sciences'', The MIT Press, pp. 579–582</ref>

Overview of the six base colors in Natural Colour System with their equivalent in hex triplet, RGB and HSV coordinates systems. However, note that these codes are only approximate, as the definition of NCS elementaries is based on perception and not production of color.

:{| class="wikitable"
|+ NCS base colors
!colspan=2 | Color !!colspan=3| [[RGB color model|RGB]] !!colspan=3| [[HSL and HSV|HSV]]
|-
|style="background:#FFF;color:#FFF;width:16px"| FFFFFF || White (#FFFFFF) || 100% || 100% || 100% || — || 0% || 100%
|-
|style="background:#000;color:#000"| 000000 || Black (#000000) || 0% || 0% || 0% || — || — || 0%
|-
|style="background:#009f6b;color:#009F6B"| 009F6B || Green (#009F6B) || 0% || 62% || 42% || 160° || 100% || 63%
|-
|style="background:#C40233;color:#C40233"| C40233  || Red (#C40233) || 77% || 1% || 20% || 345° || 99% || 77%
|-
|style="background:#FFD300;color:#FFD300"| FFD300 || Yellow (#FFD300) || 100% || 83% || 0% || 50° || 100% || 100%
|-
|style="background:#0087BD;color:#0087BD"| 0087BD  || Blue (#0087BD) || 0% || 53% || 74% || 197° || 100% || 74%
|}

==See also==
* [[Color chart]], other color systems and charts

==References==
{{reflist}}

==External links==
[https://ncscolour.com NCS Colour – Universal Language for Colour Communication] – official site
<!-- site with nasty popup's
*[http://www.procato.com/rgb/ RGB Browser with NCS color matching]
-->
<!-- Dead links
*[http://www.brf-prasthagen.se/ncs/ncs2rgb.html Another online NCS calculator]
*[http://www.polykat.de/ncs7e.htm Polykat NCS-RGB Konverter] 
*[http://looncox.ivyro.net/palette/ ToyPalette] from Loo & Cox, a web application for generating color palettes from images. NCS color analysis of digital image.
-->

{{color space}}

[[Category:Color models]]