CIE standard observer

The GIE Standard Observer. The CIE standard observer is a set of curves giving the tristimulus responses of an imaginary observer representing an average population for three primary colors arbitrarily chosen for convenience. The 1931 CIE standard observer was deterrnined for 2° foveal vision, while the later 1964 CIE supplementary standard observer appHes to a 10° vision a subscript 10 is usually used for the latter. The curves for both are given in Eigure 7 and the differences between the two observers can be seen in Table 2. The standard observers were defined in such a way that of the three primary responses x(X),jy(X), and X), the value ofjy(X) corresponds to the spectral photopic luminous efficiency, ie, to the perceived overall lightness of an object. 

CIE used the 1931 CIE standard observer to estabUsh a color representation system in which the hue and saturation could be represented on a two-dimensional diagram. Three tristimulus values X, Y, and Z are first obtained, based on the standard observer, so that the hue and saturation of two... 

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". 

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... 

Figure 3. Spectral tristimulus values according to the 1931 CIE standard observer. These values are dimensionless.

Tristimulus colorimeters are used to measure color in certain food applications. They combine light source, filters, and photodetectors to reproduce the CIE Standard Observer response functions (Fig. F5.1.8). Colorimeters, having broad band-pass filters, do not measure the spectral data. Without spectral data they cannot offer the choice of either observer or... 

Figure 6-2 Spectral Energy Distribution of Light Sources A and C, the CIE, and Relative Luminosity Function y for the CIE Standard Observer...

Color Meter. The Chroma Meter CR-300 (Minolta, Osaka, Japan) provides both accurate and precise color data (Post et al., 1993). This color meter uses a pulsed xenon light for stable and uniform illumination of the sample. Three photocells measure the photons diifusely reflected by the sample through filters matching the CIE standard observer spectral response. A standard white plate is used for calibration. For analysis, the hand-held detector unit which is protected by a glass window may be placed on top of a small pile of a powdered sample (300 mg), thus standardizing the sample surface. This way, up to one hundred samples can be precisely measured within one hour. Further advantages are the mobility of the unit, and the output of the three color parameters in several color systems (see below). 

This diagram illustrates the optical analogue process in which the properties of an instrument light source, a properly selected filter, tmd a photo-detector are combined to provide an optical analogue of the similar properties of a CIE standard iUuminant (here ILLUMINANT C) and a CIE standard observer response function (here the "y response). 

CIE standard observer n. The observer data adopted by the Commission Internationale d Eclairage to represent the response of the average human eye, when light-adapted, to an equal-energy spectrum. Unless otherwise specified, the term applies to the data adopted in 1931 for a 2° field of vision. The data adopted in 1964, sometimes called the 1964 observer, were obtained for a 10°, annular field which excludes the 2° field of the 1931 observer functions. 

Color matching functions n. Relative amounts of three additive primaries required to match each wavelength of light. The term is generally used to refer to the CIE Standard Observer color matching functions designated x + y + z. 

Trichromat tri-kro- mat [back-formation fir. trichromatic] (1929) n. Person requiring mixtures of three component primaries to match colors. Normal observers fall into this classification the CIE standard observer is defined in terms of the amounts of three primary colors required to match all spectral colors. Not all trichromats are normal, however. Some observers exhibit anomalous trichromatism, requiring abnormal proportions of three primary colors for color matching. 

X n. Special color matching functions of the CIE standard observer used for calculating the X tristimulus value. McDonald R (ed) (1997) Colour physics for industry, 2nd edn. Society of Dyers and Colourists, West Yorkshire, England. 

Y n. Special color matching function of the CIE standard observed used for calculating... 

Fig. 2.9 a Sensitivity curves for the rods (370 nm curve) and cones (445 nm curve—blue 508 nm curve—green 565 nm curve— red, orange, yellow) in the human eye b The 1931 CIE standard observer. 1980, American Chemical Society, Ref. [15]... 

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