Color space

A lot of different color space systems have been constructed and tailored for a wide variety of applications (5,7,8). 

The CIE values were established by the International Commission on Illumination (Commission Internationale de I Eclairage, CIE) (5,6,9). The original CIE standard primary light sources are narrow band light sources with red at 700 ran, green at 546 ran, and blue at 436 nm. We emphasize that the latter are incidentally the bands of from mercury lamps (10). 

The usual reference standard is the CIEXYZ color space or CIELAB color space (5,9). From this standard, other color spaces have been developed. 

The RGB color space uses additive color mixing. It is based on what kind of light needs to be emitted to produce a given color. In contrast, CMYK uses subtractive color mixing. It is used for inks or coatings and it is based on the light reflected from the substrate by which the surfaces produce a certain color. 

There are special color spaces for the application in electronic monitors, used in computers and television. 

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Experienced color matchers can achieve a good color match by trial and error without using any instmmentation. In some cases, however, this technique can be a lengthy process, and should the desired match be outside the color space defined by the available color standards, the technician might spend too much time just to determine that the match is not possible. To get the most cost-effective match using a low metamerism in the shortest possible time, the use of a computet color matching system is preferable. 

In color technology and measurement, both types of approaches are used. Color printing, for example, generally employs three colors (usually plus black), and the ever useful CIE system was founded on experiments in which colors were matched by mixtures of three primary colors, often blue, green, and red. Yet transmitted television signals are based on the opponent system, with one intensity and two color-balance signals, as are the modern representations of color, such as the CIELAB and related color spaces based on red-green and yeUow-blue opponent axes. 

The 1976 CIELUV Color Space. Properly designated CIE this uses a white object or light source designated by the subscript n as... 

The 1976 CIELAB Color Space. Defiaed at the same time as the CIELUV space, the CIELAB space, propedy designated CIE E i , is a nonlinear transformation of the 1931 CIE X, Y, Z space. It also uses the metric lightness coordinate E, together with ... 

The 1976 CIE Metric Color Spaces. Both the CIELUV and CIELAB spaces can have their Cartesian coordinates converted to cylindtical coordinates, called metric or hue-angle coordinates, with E unchanged. These coordinates are designated CIE LYC h and CIE LYC, b, respectively. 

Hunter L,a,b and Other Color Spaces. The CIELAB and CIELUV color spaces were the outgrowth of a large and complex group of interrelated early systems and have replaced essentially all of them except for the 1942 Hunter Y,a,b group of color spaces (3). This was the earliest practical opponent-based system which is still widely used. In this system, for illuminant C and the 2° standard observer ... 

In the CIELAB and CIELUV color spaces, the difference between a batch sample and a reference standard designated with a subscript s, can be designated by its components, eg, AAL = L — L. The three-dimensional total color differences are given by EucHdian geometry as the 1976 CIE lYa b and 1976 CIE lYu Y color difference formulas ... 

There are instances in which one manufacturer may designate a bluish red dye as Red 4B and another manufacturer uses Violet 2R for the same dye. To resolve such a problem the manufacturers pattern leaflets should be consulted. These show actual dyed pieces of cloth so the colors of the dyes in question can be compared directly in the actual appHcation. Alternatively, colors can be specified in terms of color space coordinates. The Cielab system is becoming the standard in this system the color of a dye is defined by three numbers, the L, a, and b coordinates (see Color). 

Color Difference Evaluation. Shade evaluation is comparable in importance to relative strength evaluation for dyes. This is of interest to both dye manufacturer and dye user for purposes of quaUty control. Objective evaluation of color differences is desirable because of the well-known variabihty of observers. A considerable number of color difference formulas that intend to transform the visually nonuniform International Commission on Illumination (CIE) tristimulus color space into a visually uniform space have been proposed over the years. Although many of them have proven to be of considerable practical value (Hunter Lab formula, Friele-MacAdam-Chickering (FMC) formula, Adams-Nickerson formula, etc), none has been found to be satisfactorily accurate for small color difference evaluation. Correlation coefficients for the correlation between average visually determined color difference values and those based on measurement and calculation with a formula are typically of a magnitude of approximately 0.7 or below. In the interest of uniformity of international usage, the CIE has proposed two color difference formulas (CIELAB and CIELUV) one of which (CIELAB) is particularly suitable for appHcation on textiles (see Color). 

The frame-grabbed interferograms with a resolution of 512 pixels by 512 lines are first transformed from RGB to CIELAB color space and they are then converted to the him thickness map using appropriate calibration and a color... 

When Munsell devised his color space, he did so on the basis of minimum observable color perception steps. But the problem with the Munsell System was one of reproducibility, which the CIE Standard Observer cured. In formulating a color match, one wants to be able to predict the correct concentration of colorants required, whose scattering and absorption properties are known, i.e.- the lightness, so as to match the sample submitted, starting with their spectrophotometric curves. In practice, this is not so simple, since two colors must have identical spectrophotometric curves to be exactly equal. It turns out that the human eye will identify the two colors to be equal if their spectrophotometric reflectances are reasonably close. Two colors may appear to be equal under Daylight illumination, but quite different under incandescent lamp illumination. These colors are known zus "metamers" and the phenomenon "metamerism". 

The HunterLab system (1958) was the hrst to use the opponent color theory stating that the red, green, and blue cone responses are re-mixed into opponent coders as they move up the optic nerve to the brain.Based on that theory, the HunterLab color space is three-dimensional and rectangular (see Figure 1.6). 

Adams-Nickerson color space, 7 320 Adapalene, 25 789 Adapress, molecular formula and structure, 5 128t Adaptive control system, 20 698 Adaptive sampling techniques, 26 1016-1019... 

CIE color system, 7 304. See also Commission Internationale de l clairage (CIE) chromacity diagrams, 7 313-315 standard illuminants, 7 315-316 CIEDE200 color difference equation, 7 322 CIELAB, 7 304 CIELAB Color Space, 7 320 CIELAB color values, of flax fiber, 11 614t Cielab dye nomenclature system, 9 244 CIELAB Metric Color Spaces, 7 320 CIELAB system, 19 428, 451 CIELUV Color Space, 7 319-320 CIE Standard Observer, 7 311-312 Cigarette filters... 

Hunig s Base, 2 549t Hunter Color Spaces, 7 321 Hunter-Nash procedure, 10 757 Huntsman fixed-bed maleic anhydride process, 15 501... 

Here both, ta and Aa> are the antisymmetric generators of 87/(3), i.e., the antisymmetric Gell-Mann matrices (A, A e 2,5,7 ), acting in flavor and color space, respectively. In the two-flavor color superconducting phase (2SC) where only the light quarks are involved in the condensation, the flavor index in Eq. (1) is restricted to A = 2. In this case it is always possible, without loss of generality, to perform a color rotation such that the 2SC phase is described by s22 / 0 and saa = 0 if (A, A ) (2,2). 

It is instructive to start with the excitation spectrum in the case of the ordinary 2SC phase when dfi = 0. With the conventional choice of the gap pointing in the anti-blue direction in color space, the blue quarks are not affected by the pairing dynamics, and the other four quasi-particle excitations are linear superpositions of ur>g and dr(J quarks and holes. The quasi-particle is nearly identical with a quark at large momenta and with a hole at small momenta. We represent the quasi-particle in the form of Q(quark, hole), then the four quasiparticles can be represented explicitly as Q(ur,dg), Q(ug, dr), Q(dr,ug) and Q(dg,ur). When S/i = 0, the four quasi-particles are degenerate, and have a common gap A. 

Commission Internationale de I Eclairage (1978) Recommendations on uniform color spaces, color difference and psychometric color terms. Supplement No. 2. Publ. No. 15. Colorimetry, CIE 1971, Paris Condon, N.G. Leibsle, F.M. Lennie, A.R. Murray, P.W. Parker,T.M. Vaughan D.S. Thornston, G. (1998) Scanning tunnelling microscopy studies of a-Fe203 (0001). Surface Sd. 397 278-287... 

Fig. 2. We show the electron localization function (ELF) of (from left to right and from above to below) the Cl-, the AlCLj-, the 12 1 , the A12C17-, and the AI4CI13- species. The purple colored space indicates high values of ELF or electron pairs. Therefore, electron deficiency can be recognized from the half open spheres.

In the work with cottonseed flours, we used the Hunterlab color meter D25D2A and expressed these measurements as Hunter L, a, b color values. These are coordinates of the three-dimensional opponent-color space shown in Figure 2. The L value measures lightness, or the amount of light reflected or transmitted by the object. The a and b values are the chromaticity coordinates from which information about hue and saturation can be obtained. The a value measures redness when plus and greenness when minus. The b value measures yellowness when plus and blueness when minus. 

Colorimetry [1.17] - [1.19]. The principles of colorimetry are based on the fact that all color stimuli can be simulated by additively mixing only three selected color stimuli (trichromatic principle). A color stimulus can, however, also be produced by mixing the spectral colors. Thus, it has a spectral distribution, which in the case of nonluminous, perceived colors is called the spectral reflectance q (2). After defining three reference stimuli, the trichromatic principle allows a three-dimensional color space to be built up in which the color coordinates (tristimulus values) can be interpreted as components of a vector (CIE system for standards, see Table 1, Colorimetry CIE = Commission Internationale de l Eclairage). For uncolored illumination the three CIE tristimulus values depend on the spectral reflectance as follows ... 

The color difference is finally calculated as the geometrical distance between the two positions in the CIELAB color space ... 

An important advantage of the CIELAB system is that the resulting color difference can be split up into component contributions, namely lightness, saturation, and hue, corresponding to the arrangement of the color space ... 

The sequence of interference colors obtained with increasing Ti02 layer thickness agrees with theoretical calculations in the color space [5.206], [5.224], [5.225]. An experimental development of L a b values is given in Figure 78. 

The eye, as amazing as it is, cannot measure color quantitatively. Color-order systems have been developed to specify color based on a space with coordinates. Color can be presented as an arrangement of three dimensions within a color space. One dimension relates to a lightness attribute and the other two are chromatic attributes, referred to as hue and chroma (or saturation). The human observer is not equally... 

The subject of color, as it relates to the human eye and brain, is complex and fascinating. Overall, there are many factors that can affect the perceived color of a surface. Models like Munsell use an alphanumeric notation to identify the dimensions for a color and its location within the color space. A Munsell notation (hue, value, and chroma) depends on a subjective visual judgment made by a human observer. There are other color-order systems that specify color by objective three-dimen-... 

Figure F5.1.10 The Hunter L,a,b color space was designed for measuring color differences. Figure courtesy of GretagMacbeth. This black and white facsimile of the figure is intended only as a placeholder for full-color version of figure go to http //www.currentprotocols.com/colorfigures...

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