色度

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色度(光の色を数量的に表したもの)

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/09/05 13:50:28」(JST)

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The CIE 1931 xy chromaticity space, also showing the chromaticities of black-body light sources of various temperatures, and lines of constant correlated color temperature

Chromaticity is an objective specification of the quality of a color regardless of its luminance. Chromaticity consists of two independent parameters, often specified as hue (h) and colorfulness (s), where the latter is alternatively called saturation, chroma, intensity,^[1] or excitation purity.^[2]^[3] This number of parameters follows from trichromacy of vision of most humans, which is assumed in most models in the color science.

Quantitative description

In color science, the white point of an illuminant or of a display is a neutral reference characterized by a chromaticity; all other chromaticities may be defined in relation to this reference using polar coordinates. The hue is the angular component, and the purity is the radial component, normalized^{[clarification needed]} by the maximum radius for that hue.

Purity is roughly equivalent to the term "saturation" in the HSV color model. The property "hue" is as used in general color theory and in specific color models such as HSV and HSL color spaces, though it is more perceptually uniform in color models such as Munsell, CIELAB or CIECAM02.

Some color spaces separate the three dimensions of color into one luminance dimension and a pair of chromaticity dimensions. For example, the white point of an sRGB display is an $x$ , $y$ chromaticity of (0.3127, 0.3290), where $x$ and $y$ coordinates are used in the xyY space.

(u', v')

, the chromaticity in CIELUV, is a pretty perceptionally uniform presentation of the chromaticity as (another than in CIE 1931) planar Euclidean shape. This presentation is a projective transformation of the CIE 1931 chromaticity diagram above.

These pairs determine a chromaticity as affine coordinates on a triangle in a 2-space, which contains all possible chromaticities. These $x$ and $y$ are used because of simplicity of expression in CIE 1931 (see below) and have no inherent advantage. Other coordinate systems on the same X-Y-Z triangle, or other color triangles, can be used.

On the other hand, some color spaces such as RGB and XYZ do not separate out chromaticity; though chromaticity is defined by a mapping that normalizes out intensity and its coordinates, such as $r$ and $g$ or $x$ and $y$ , can be calculated through the division operation, such as $x =$ X/X + Y + Z and so on.

The xyY space is a cross between the CIE XYZ and its normalized chromaticity coordinates xyz, such that the luminance Y is preserved and augmented with just the required two chromaticity dimensions.^[4]

References

^ In modern terminology the word "intensity" may refer to lightness, not to colorfulness.
^ Emil Wolf (1961). Progress in Optics. North Holland Pub. Co.
^ Leslie D. Stroebel, Richard D. Zakia (1993). The Focal Encyclopedia of Photography. Focal Press. ISBN 0-240-51417-3.
^ Charles A. Poynton (2003). Digital Video and HDTV: Algorithms and Interfaces. Morgan Kaufmann. ISBN 1-55860-792-7.

External links

Stanford University CS 178 interactive Flash demo explaining chromaticity diagrams.

English Journal

Synthesis of blue emitting InP/ZnS quantum dots through control of competition between etching and growth.

Lim K, Jang HS, Woo K.SourceMolecular Recognition Research Center, Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul 130-650, Republic of Korea.
Nanotechnology.Nanotechnology.2012 Dec 7;23(48):485609. doi: 10.1088/0957-4484/23/48/485609. Epub 2012 Nov 9.
Blue (<480 nm) emitting Cd-free quantum dots (QDs) are in great demand for various applications. However, their synthesis has been challenging. Here we present blue emitting InP/ZnS core/shell QDs with a band edge emission of 475 nm and a full width at half maximum of 39 nm (215 meV) from the
PMID 23138715

Eu2+-Activated Sr8ZnSc(PO4)7: A Novel Near-Ultraviolet Converting Yellow-Emitting Phosphor for White Light-Emitting Diodes.

Huang CH, Chiu YC, Yeh YT, Chan TS, Chen TM.AbstractThe crystal structure of Eu2+-activated Sr8ZnSc(PO4)7:Eu2+ phosphor was refined and determined from XRD profiles by the Rietveld refinement method using a synchrotron light source. This phosphor crystallizes in the monoclinic structure with the I2/a space group. The SZSP:xEu2+ phosphors showed a broad yellow emission band centered at 511 and 571 nm depending on the concentration of Eu2+, and the composition-optimized concentration of Eu2+ in the Sr8ZnSc(PO4)7:Eu2+ phosphor was determined to be 2 mol%. The estimated crystal-field splitting and CIE chromaticity coordinates of Sr8ZnSc(PO4)7:xEu2+ (x = 0.001-0.05 mol) were 20181 ~ 20983 cm-1 and (0.3835, 0.5074) ~ (0.4221, 0.5012), respectively, and the emission band showed a redshift from 547 to 571 nm with increasing Eu2+ concentration. The non-radiative transitions between the Eu2+ ions in the Sr8ZnSc(PO4)7 host were attributable to dipole-dipole interactions, and the critical distance was approximately 19.8 Å. The combination of a 400 nm NUV chip with a blend of Sr8ZnSc(PO4)7:0.02Eu2+ and BAM:Eu2+ phosphors (light converters) gave high color rendering indices between 79.38 to 92.88, correlated color temperatures between 4325 K ~ 7937 K, and tuned CIE chromaticity coordinates in the range (0.381, 0.435) ~ (0.294, 0.310), respectively, depending on the SZSP:0.02Eu2+/BAM:Eu2+ weight ratio. These results suggest that the Sr8ZnSc(PO4)7:0.02Eu2+/BAM:Eu2+ phosphor blend has potential applications in white NUV LEDs.
ACS applied materials & interfaces.ACS Appl Mater Interfaces.2012 Nov 21. [Epub ahead of print]
The crystal structure of Eu2+-activated Sr8ZnSc(PO4)7:Eu2+ phosphor was refined and determined from XRD profiles by the Rietveld refinement method using a synchrotron light source. This phosphor crystallizes in the monoclinic structure with the I2/a space group. The SZSP:xEu2+ phosphors showed a bro
PMID 23167702

Japanese Journal

Document color modification with hatching for color vision defectives (福祉情報工学)

KOSHI Takaaki,HASHIMOTO Naotaka,OHTA Naoya [他]
電子情報通信学会技術研究報告 = IEICE technical report : 信学技報 114(512), 159-163, 2015-03-13
NAID 40020428936

ヒトの色と明度の恒常性を模擬したカラー画像処理形態 (スマートインフォメディアシステム)

有井栞,田口亮
電子情報通信学会技術研究報告 = IEICE technical report : 信学技報 114(496), 11-16, 2015-03-05
NAID 40020431133

Fabrication of sodium borosilicate glass and Eu-doped SiAlON composites for white LED

,
Journal of the Ceramic Society of Japan 123(1437), 452-455, 2015
… The chromaticity of the composites, which was estimated from photoluminescence spectra, changed from blue to yellow with increasing SiAlON concentration and sample thickness. …
NAID 130005068658