In colorimetry , the CIE 1976 L *, u *, v * color space , commonly known by its abbreviation CIELUV , is a color space adopted by the International Commission on Illumination (CIE) in 1976, as a simple-to-compute transformation of the 1931 CIE XYZ color space , but which attempted perceptual uniformity . It is extensively used for applications such as computer graphics which deal with colored lights. Although additive mixtures of different colored lights will fall on a line in CIELUV's uniform chromaticity diagram (called the CIE 1976 UCS ), such additive mixtures will not, contrary to popular belief, fall along a line in the CIELUV color space unless the mixtures are constant in lightness .
46-541: CIELUV is an Adams chromatic valence color space and is an update of the CIE 1964 ( U *, V *, W *) color space (CIEUVW). The differences include a slightly modified lightness scale and a modified uniform chromaticity scale, in which one of the coordinates, v ′, is 1.5 times as large as v in its 1960 predecessor . CIELUV and CIELAB were adopted simultaneously by the CIE when no clear consensus could be formed behind only one or
92-553: A digital representation. A color space may be arbitrary, i.e. with physically realized colors assigned to a set of physical color swatches with corresponding assigned color names (including discrete numbers in – for example – the Pantone collection), or structured with mathematical rigor (as with the NCS System , Adobe RGB and sRGB ). A "color space" is a useful conceptual tool for understanding
138-461: A linear space (vector space)... became widely known around 1920, when Hermann Weyl and others published formal definitions. In fact, such a definition had been given thirty years previously by Peano , who was thoroughly acquainted with Grassmann's mathematical work. Grassmann did not put down a formal definition—the language was not available—but there is no doubt that he had the concept. With this conceptual background, in 1853, Grassmann published
184-685: A Cartesian coordinate pair. Furthermore, the saturation correlate can be defined as Similar correlates of chroma and hue, but not saturation, exist for CIELAB. See Colorfulness for more discussion on saturation. The color difference can be calculated using the Euclidean distance of the ( L *, u *, v *) coordinates. It follows that a chromaticity distance of ( Δ u ′ ) 2 + ( Δ v ′ ) 2 = 1 / 13 {\displaystyle {\sqrt {(\Delta u')^{2}+(\Delta v')^{2}}}=1/13} corresponds to
230-523: A class of color spaces suggested by Elliot Quincy Adams . Two important Adams chromatic valence spaces are CIELUV and Hunter Lab . Chromatic value/valence spaces are notable for incorporating the opponent process model and the empirically-determined 2 + 1 ⁄ 2 factor in the red/green vs. blue/yellow chromaticity components (such as in CIELAB ). In 1942, Adams suggested chromatic value color spaces. Chromatic value, or chromance , refers to
276-417: A color model with no associated mapping function to an absolute color space is a more or less arbitrary color system with no connection to any globally understood system of color interpretation. Adding a specific mapping function between a color model and a reference color space establishes within the reference color space a definite "footprint", known as a gamut , and for a given color model, this defines
322-459: A color space. For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB color model. When defining a color space, the usual reference standard is the CIELAB or CIEXYZ color spaces, which were specifically designed to encompass all colors the average human can see. Since "color space" identifies a particular combination of the color model and the mapping function,
368-471: A graphic or document is sometimes called tagging or embedding ; tagging, therefore, marks the absolute meaning of colors in that graphic or document. A color in one absolute color space can be converted into another absolute color space, and back again, in general; however, some color spaces may have gamut limitations, and converting colors that lie outside that gamut will not produce correct results. There are also likely to be rounding errors, especially if
414-409: A theory of how colors mix; it and its three color laws are still taught, as Grassmann's law . As noted first by Grassmann... the light set has the structure of a cone in the infinite-dimensional linear space. As a result, a quotient set (with respect to metamerism) of the light cone inherits the conical structure, which allows color to be represented as a convex cone in the 3- D linear space, which
460-650: Is a new international digital video color space standard published by the IEC (IEC 61966-2-4). It is based on the ITU BT.601 and BT.709 standards but extends the gamut beyond the R/G/B primaries specified in those standards. HSV ( h ue, s aturation, v alue), also known as HSB (hue, saturation, b rightness) is often used by artists because it is often more natural to think about a color in terms of hue and saturation than in terms of additive or subtractive color components. HSV
506-419: Is a transformation of an RGB color space, and its components and colorimetry are relative to the RGB color space from which it was derived. HSL ( h ue, s aturation, l ightness/ l uminance), also known as HLS or HSI (hue, saturation, i ntensity) is quite similar to HSV , with "lightness" replacing "brightness". The difference is that the brightness of a pure color is equal to the brightness of white, while
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#1732772139290552-415: Is based on CIEUVW and is another attempt to define an encoding with uniformity in the perceptibility of color differences . The non-linear relations for L *, u *, and v * are given below: The quantities u ′ n and v ′ n are the ( u ′, v ′) chromaticity coordinates of a "specified white object" – which may be termed the white point – and Y n is its luminance. In reflection mode, this
598-417: Is increasingly seen in the information visualization community as a way to help with presenting data without the bias implicit in using varying saturation . The cylindrical version of CIELUV is known as CIELCh uv , or CIELChuv, CIELCh(uv) or CIEHLC uv , where C * uv is the chroma and h uv is the hue : where atan2 function, a "two-argument arctangent", computes the polar angle from
644-720: Is intended to make radial distance from the white point correlate with the Munsell chroma along any one hue radius (i.e., to make the diagram perceptually uniform). For achromatic surfaces, ( y n / x n ) X = Y = ( y n / z n ) Z , {\displaystyle (y_{n}/x_{n})X=Y=(y_{n}/z_{n})Z,} and hence V X − V Y = 0 , {\displaystyle V_{X}-V_{Y}=0,} V Z − V Y = 0. {\displaystyle V_{Z}-V_{Y}=0.} In other words,
690-458: Is often (but not always) taken as the ( u ′, v ′) of the perfect reflecting diffuser under that illuminant. (For example, for the 2° observer and standard illuminant C, u ′ n = 0.2009 , v ′ n = 0.4610 .) Equations for u ′ and v ′ are given below: The transformation from ( u ′, v ′) to ( x , y ) is: The transformation from CIELUV to XYZ is performed as follows: CIELCh uv , or HCL color space (hue–chroma–luminance)
736-461: Is referred to as the color cone. Colors can be created in printing with color spaces based on the CMYK color model , using the subtractive primary colors of pigment ( c yan , m agenta , y ellow , and blac k ). To create a three-dimensional representation of a given color space, we can assign the amount of magenta color to the representation's X axis , the amount of cyan to its Y axis, and
782-464: Is sometimes referred to as absolute, though it also needs a white point specification to make it so. A popular way to make a color space like RGB into an absolute color is to define an ICC profile, which contains the attributes of the RGB. This is not the only way to express an absolute color, but it is the standard in many industries. RGB colors defined by widely accepted profiles include sRGB and Adobe RGB . The process of adding an ICC profile to
828-429: Is the 24- bit implementation, with 8 bits, or 256 discrete levels of color per channel . Any color space based on such a 24-bit RGB model is thus limited to a range of 256×256×256 ≈ 16.7 million colors. Some implementations use 16 bits per component for 48 bits total, resulting in the same gamut with a larger number of distinct colors. This is especially important when working with wide-gamut color spaces (where most of
874-534: Is the basis for almost all other color spaces. The CIERGB color space is a linearly-related companion of CIE XYZ. Additional derivatives of CIE XYZ include the CIELUV , CIEUVW , and CIELAB . RGB uses additive color mixing, because it describes what kind of light needs to be emitted to produce a given color. RGB stores individual values for red, green and blue. RGBA is RGB with an additional channel, alpha, to indicate transparency. Common color spaces based on
920-450: Is the translation of the representation of a color from one basis to another. This typically occurs in the context of converting an image that is represented in one color space to another color space, the goal being to make the translated image look as similar as possible to the original. The RGB color model is implemented in different ways, depending on the capabilities of the system used. The most common incarnation in general use as of 2021
966-445: Is very perceptually non-uniform: small perceptual changes in chromaticity in greens, for example, translate into large distances , while larger perceptual differences in chromaticity in other colors are usually much smaller. Adams suggested a relatively simple uniform chromaticity scale in his 1942 paper: where x n , y n , z n {\displaystyle x_{n},y_{n},z_{n}} are
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#17327721392901012-594: The Munsell value for lightness. Defining chromatic valence components W X = ( x / x n y / y n − 1 ) V J {\displaystyle W_{X}=\left({\frac {x/x_{n}}{y/y_{n}}}-1\right)V_{J}} and W Z = ( z / z n y / y n − 1 ) V J {\displaystyle W_{Z}=\left({\frac {z/z_{n}}{y/y_{n}}}-1\right)V_{J}} , we can determine
1058-517: The Munsell-Sloan-Godlove value function is applied to the tristimulus value indicated in the subscript. (Note that the two spaces use different lightness approximations.) Color space A color space is a specific organization of colors . In combination with color profiling supported by various physical devices, it supports reproducible representations of color – whether such representation entails an analog or
1104-659: The difference between two colors as: where V J is the Newhall-Nickerson-Judd value function and the 0.4 factor is incorporated to better make differences in W X and W Z perceptually correspond to one another. In chromatic value color spaces, the chromaticity components are W X = V X − V Y {\displaystyle W_{X}=V_{X}-V_{Y}} and W Z = V Z − V Y {\displaystyle W_{Z}=V_{Z}-V_{Y}} . The difference is: where
1150-430: The lightness of a pure color is equal to the lightness of a medium gray. Early color spaces had two components. They largely ignored blue light because the added complexity of a 3-component process provided only a marginal increase in fidelity when compared to the jump from monochrome to 2-component color. In color science , there are two meanings of the term absolute color space : In this article, we concentrate on
1196-595: The RGB model include sRGB , Adobe RGB , ProPhoto RGB , scRGB , and CIE RGB . CMYK uses subtractive color mixing used in the printing process, because it describes what kind of inks need to be applied so the light reflected from the substrate and through the inks produces a given color. One starts with a white substrate (canvas, page, etc.), and uses ink to subtract color from white to create an image. CMYK stores ink values for cyan, magenta, yellow and black. There are many CMYK color spaces for different sets of inks, substrates, and press characteristics (which change
1242-626: The X, Y, and Z axes. Colors generated on a given monitor will be limited by the reproduction medium, such as the phosphor (in a CRT monitor ) or filters and backlight ( LCD monitor). Another way of creating colors on a monitor is with an HSL or HSV color model, based on hue , saturation , brightness (value/lightness). With such a model, the variables are assigned to cylindrical coordinates . Many color spaces can be represented as three-dimensional values in this manner, but some have more, or fewer dimensions, and some, such as Pantone , cannot be represented in this way at all. Color space conversion
1288-451: The amount of yellow to its Z axis. The resulting 3-D space provides a unique position for every possible color that can be created by combining those three pigments. Colors can be created on computer monitors with color spaces based on the RGB color model , using the additive primary colors ( red , green , and blue ). A three-dimensional representation would assign each of the three colors to
1334-426: The chromaticities of the reference white object (the n suggests normalized ). (Adams had used smoked magnesium oxide under CIE Illuminant C , but these would be considered obsolete today. This exposition is generalized from his papers.) Objects which have the same chromaticity coordinates as the white object usually appear neutral, or fairly so, and normalizing in this fashion ensures that their coordinates lie at
1380-497: The chromaticity of the sample. Accordingly, he called their plot a "constant-brightness chromaticity diagram". This diagram does not have the white point at the origin, but at (1, 1) instead. Chromatic valence spaces incorporate two relatively perceptually uniform elements: a chromaticity scale and a lightness scale. The lightness scale, determined using the Newhall–Nickerson–Judd value function , forms one axis of
1426-428: The color capabilities of a particular device or digital file. When trying to reproduce color on another device, color spaces can show whether shadow/highlight detail and color saturation can be retained, and by how much either will be compromised. A " color model " is an abstract mathematical model describing the way colors can be represented as tuples of numbers (e.g. triples in RGB or quadruples in CMYK ); however,
CIELUV - Misplaced Pages Continue
1472-460: The color space: The remaining two axes are formed by multiplying the two uniform chromaticity coordinates by the lightness, V J : This is essentially what Hunter used in his Lab color space . As with chromatic value, these functions are plotted with a scale factor of 2 + 1 ⁄ 2 to give nearly equal radial distance for equal changes in Munsell chroma. Adams' color spaces rely on
1518-731: The color. It is similar to the YUV scheme used in most video capture systems and in PAL ( Australia , Europe , except France , which uses SECAM ) television, except that the YIQ color space is rotated 33° with respect to the YUV color space and the color axes are swapped. The YDbDr scheme used by SECAM television is rotated in another way. YPbPr is a scaled version of YUV. It is most commonly seen in its digital form, YCbCr , used widely in video and image compression schemes such as MPEG and JPEG . xvYCC
1564-410: The conversion between them should maintain the same color. However, in general, converting between two non-absolute color spaces (for example, RGB to CMYK ) or between absolute and non-absolute color spaces (for example, RGB to L*a*b*) is almost a meaningless concept. A different method of defining absolute color spaces is familiar to many consumers as the swatch card, used to select paint, fabrics, and
1610-469: The dot gain or transfer function for each ink and thus change the appearance). YIQ was formerly used in NTSC ( North America , Japan and elsewhere) television broadcasts for historical reasons. This system stores a luma value roughly analogous to (and sometimes incorrectly identified as) luminance , along with two chroma values as approximate representations of the relative amounts of blue and red in
1656-473: The eye, each of which was sensitive to a particular range of visible light. Hermann von Helmholtz developed the Young–Helmholtz theory further in 1850: that the three types of cone photoreceptors could be classified as short-preferring ( blue ), middle-preferring ( green ), and long-preferring ( red ), according to their response to the wavelengths of light striking the retina . The relative strengths of
1702-505: The intensity of the opponent process responses and is derived from Adams' theory of color vision. A chromatic value space consists of three components: A chromatic value diagram is a plot of V X − V Y {\displaystyle V_{X}-V_{Y}} (horizontal axis) against 0.4 ( V Z − V Y ) {\displaystyle 0.4(V_{Z}-V_{Y})} (vertical axis). The 2 + 1 ⁄ 2 scale factor
1748-506: The more common colors are located relatively close together), or when a large number of digital filtering algorithms are used consecutively. The same principle applies for any color space based on the same color model, but implemented at different bit depths . CIE 1931 XYZ color space was one of the first attempts to produce a color space based on measurements of human color perception (earlier efforts were by James Clerk Maxwell , König & Dieterici, and Abney at Imperial College ) and it
1794-465: The origin. Adams plotted the first one the horizontal axis and the latter, multiplied by 0.4, on the vertical axis. The scaling factor is to ensure that the contours of constant chroma (saturation) lie on a circle. Distances along any radius from the origin are proportional to colorimetric purity . The chromance diagram is not invariant to brightness, so Adams normalized each term by the Y tristimulus value: These expressions, he noted, depended only on
1840-598: The other of these two color spaces. CIELUV uses Judd-type (translational) white point adaptation (in contrast with CIELAB, which uses a von Kries transform ). This can produce useful results when working with a single illuminant, but can predict imaginary colors (i.e., outside the spectral locus ) when attempting to use it as a chromatic adaptation transform . The translational adaptation transform used in CIELUV has also been shown to perform poorly in predicting corresponding colors. By definition, 0 ≤ L * ≤ 100 . CIELUV
1886-558: The popular range of only 256 distinct values per component ( 8-bit color ) is used. One part of the definition of an absolute color space is the viewing conditions. The same color, viewed under different natural or artificial lighting conditions, will look different. Those involved professionally with color matching may use viewing rooms, lit by standardized lighting. Occasionally, there are precise rules for converting between non-absolute color spaces. For example, HSL and HSV spaces are defined as mappings of RGB. Both are non-absolute, but
CIELUV - Misplaced Pages Continue
1932-454: The same Δ E * uv as a lightness difference of Δ L * = 1 , in direct analogy to CIEUVW. The Euclidean metric can also be used in CIELCh, with that component of Δ E * uv attributable to difference in hue as Δ H * = √ C * 1 C * 2 2 sin (Δ h /2) , where Δ h = h 2 − h 1 . Adams chromatic valence color space Adams chromatic valence color spaces are
1978-483: The second definition. CIEXYZ , sRGB , and ICtCp are examples of absolute color spaces, as opposed to a generic RGB color space . A non-absolute color space can be made absolute by defining its relationship to absolute colorimetric quantities. For instance, if the red, green, and blue colors in a monitor are measured exactly, together with other properties of the monitor, then RGB values on that monitor can be considered as absolute. The CIE 1976 L*, a*, b* color space
2024-525: The signals detected by the three types of cones are interpreted by the brain as a visible color. But it is not clear that they thought of colors as being points in color space. The color-space concept was likely due to Hermann Grassmann , who developed it in two stages. First, he developed the idea of vector space , which allowed the algebraic representation of geometric concepts in n -dimensional space . Fearnley-Sander (1979) describes Grassmann's foundation of linear algebra as follows: The definition of
2070-564: The white point is at the origin. Constant differences along the chroma dimension did not appear different by a corresponding amount, so Adams proposed a new class of spaces, which he termed chromatic valence . These spaces have "nearly equal radial distances for equal changes in Munsell chroma". In chromaticity scales, lightness is factored out, leaving two dimensions. Two lights with the same spectral power distribution , but different luminance, will have identical chromaticity coordinates. The familiar CIE ( x , y ) chromaticity diagram
2116-467: The word is often used informally to identify a color model. However, even though identifying a color space automatically identifies the associated color model, this usage is incorrect in a strict sense. For example, although several specific color spaces are based on the RGB color model , there is no such thing as the singular RGB color space . In 1802, Thomas Young postulated the existence of three types of photoreceptors (now known as cone cells ) in
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