CIE 1931 Standard

Figure 5.5.10-2 A comparison of various sets of spectrums. Vertical bars, R, G B are theoretical components used by the CIE 1931 Standard Colorimetric Observer. Solid curves are probable sensitivity curves of the three types of cones using the words of Hunt in 1991. Dashed lines are the theoretical spectra of the photoreceptors based on this work when excited and viewed axially.

Figure 3 CIE 1931 Standard Colorimetric Observer curve. CIE, Commission Internationale de I Eclairage.

CIE 1931 standard observer Set of curves obtained by averaging the results of color matching experiments performed in 1931 for noncolor defective observers. The relative luminances of the colors of the spectrum were matched by mixtures of three spectral stimuH. The curves are often called color matching curves. 

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. 

The A(A), y(A), and z(A) terms were derived by the CIE from data obtained in visual experiments where observers matched colors obtained by the mixing of the blue, green, and red primary colors. The average result for human observers were defined as the CIE 1931 2° standard observer, and the wavelength dependencies of these color-matching functions are illustrated in Fig. 6. 

Fig. 6 Color-matching functions Jc(A), and z(A) of the CIE 1931 2° standard observer. (Data adapted from Ref. 40.)...

For the blue pixel, the standard CIE 1931 color chromaticity coordinates are (0.14-0.16, 0.11-0.15). Since a relatively large band gap is required for blue emitters, the appropriate blue host materials with even larger band gap are needed to optimize the energy transfer requirements. The main challenge in designing the blue emitter or its host is the device stability. 

The standard CIE 1931 "xy" chro-maticity diagram3, with "pure" colors, and their wavelength in nometers, on the periphery. 

Chromaticity coordinates n. General The two dimensions of any color order system which exclude the lightness dimension and describe the chromaticity. Thus, x and y, or a and b, or u and v, or YB and RG, may be considered as chromaticity coordinates in various color spaces. Unless otherwise specified, the term chromaticity coordinates is assumed to refer to the CIE coordinates x, y, and zfor Illuminant C and the 2° (1931) Standard Observer. 

The tables incorporated into color calculating routines by spectrophotometer manufacturers can be found in the ASTM publication Standard Test Method for Computing the Color of Objects by Using the CIE System (90). This ASTM standard is a compilation of calculated product tables for various illuminants with the two standard observers for color matching. Both standard observers are used in various industries to specify color. The operator must choose which observer is to be incorporated into the color calculations for the measured specimens. The overall difference in the color of an object observed by the 10° CIE 1964 Supplementary Observer or the 2° CIE 1931 Observer is usually small but noticeable. This is due to an uneven distribution of cone receptors in the retina of the standard eye. At a solid acceptance (cone) angle of 2°, light from the object activates the cones around the fovea, which are relatively close together and allow maximum... 

K and appears to be bluish white. The CIE Standard Illuminant D65 (Figure 12.2b) is a commonly used standard illuminant that tries to portray standard illumination conditions in the open air in different parts of the world. It represents average daylight and has a CCT of approximately 6500 K (exactly 6504 K). The CIE 1931 color space chromaticity coordinates of D65 are x = 0.3128,3 = 0.3290, which is close to a white-point in the CIE diagram. 

Instrument Sensor, shall provide a beam for illuminating the sample cell in transmission. The instrument shall be capable of converting light measured in total transmission through the sample cell to QE X Y Z tristimuius color values for the measurement conditions of CIE illuminant C and the CIE 1931 2 d ree standard observer as described in Practices E 179 and Test Method E 308. 

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... 

Fig. 8. The 1931 CIE chromaticity diagram showing wavelengths in nm and energies in eV. The central point W (for white) corresponds to standard...

Clearly, standardized light sources are desirable for color matching, particularly in view of the phenomenon of illuminant metamerism described below. Over the years CIE has defined several standard illuminants, some of which can be closely approximated by practical sources. In 1931 there was Source A, defined as a tungsten filament incandescent lamp at a color temperature of 2854 K. Sources B and C used filtering of A to simulate noon sunlight and north sky daylight, respectively. Subsequently a series of D illuminants was estabUshed to better represent natural daylight. Of these the most important is Illuminant E). ... 

The proper implementation of the CIE system requires use of a standard illumination source for calculation of the tristimulus values. Three standard sources were recommended in the 1931 CIE system, and these may be presented in terms of color temperatures (the temperature at which the color of a black-body radiator matches that of the illuminant). The, simplest source is an incandescent lamp, operating at a color temperature of 2856 K. The other two sources are combinations of lamps and solution filters designed to provide the equivalent of sunlight at noon, or the daylight associated with an overcast sky. The latter two sources are equivalent to color temperatures of 5000 K and 6800 K, respectively. 

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

The first standard observer was defined by the CIE in 1931. This was based upon a series of colour-matching experiments carried out four years earlier and... 

The CIE system for expressing color in objective terms was first presented in 1931 and has survived with relatively few modifications. The starting point is a standard observer, or rather a suitably filtered photocell, and a standard white light source. White light or a... 

Figure 2 The 1931 CIE x, g) chromaticity diagram for a 2° observer, showing the Planckian locus and the chromaticities of standard illuminants A, C, and Des.

CIE color notation system n. Colorimetric specification system based on stimulus-response characteristics adopted by the CIE in 1931. The current recommendations for the system may be obtained from the official publication, CIE Publication No. 15 (E-1.3.1) 1971, Colorimetry Official Recommendation of the International Commission on Illumination , available from National Bureau of Standards and Technology, Washington, DC. 

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. 

Observer, standard n. The spectral response characteristics of the average observer defined by the CIE. Two such sets of data are defined, the 1931 data for the 2° visual field (distance viewing) and the 1964 data for the annular 10° visual field (approximately arm s length viewing). By custom, the assumption is made that if the observer is not specified the tristimulus data has been calculated for the 1931, or 2° field observer. The use of the 1964 data should be specified. 

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