Contents 1 Saturation 2 Excitation purity 3 Chroma in CIE 1976 L*a*b* and L*u*v* color spaces 3.1 Chroma in color appearance models 4 References

Saturation Saturation scale (0% at bottom, corresponding to black and white). Saturation is one of three coordinates in the HSL and HSV color spaces. The saturation of a color is determined by a combination of light intensity and how much it is distributed across the spectrum of different wavelengths. The purest (most saturated) color is achieved by using just one wavelength at a high intensity, such as in laser light.[citation needed] If the intensity drops, then as a result the saturation drops. To desaturate a color of given intensity in a subtractive system (such as watercolor), one can add white, black, gray, or the hue's complement. Various correlates of saturation follow. CIELUV  The chroma normalized by the lightness: s u v = C u v ∗ L ∗ = 13 ( u ′ − u n ′ ) 2 + ( v ′ − v n ′ ) 2 {\displaystyle s_{uv}={\frac {C_{uv}^{*}}{L^{*}}}=13{\sqrt {(u'-u'_{n})^{2}+(v'-v'_{n})^{2}}}} where (u′n, v′n) is the chromaticity of the white point, and chroma is defined below.[8] By analogy, in CIELAB this would yield: s a b = C a b ∗ L ∗ = a ∗ 2 + b ∗ 2 L ∗ {\displaystyle s_{ab}={\frac {C_{ab}^{*}}{L^{*}}}={\frac {\sqrt {{a^{*}}^{2}+{b^{*}}^{2}}}{L^{*}}}} The CIE has not formally recommended this equation since CIELAB has no chromaticity diagram, and this definition therefore lacks direct correlation with older concepts of saturation.[9] Nevertheless, this equation provides a reasonable predictor of saturation, and demonstrates that adjusting the lightness in CIELAB while holding (a*, b*) fixed does affect the saturation. But the following formula is in agreement with the human perception of saturation: The formula proposed by Eva Lübbe is in agreement with the verbal definition of Manfred Richter: Saturation is the proportion of pure chromatic color in the total color sensation.[10] S a b = C a b ∗ C a b ∗ 2 + L ∗ 2 100 % {\displaystyle S_{ab}={\frac {C_{ab}^{*}}{\sqrt {{C_{ab}^{*}}^{2}+{L^{*}}^{2}}}}100\%} where Sab is the saturation, L* the lightness and C*ab is the chroma of the color. CIECAM02  The square root of the colorfulness divided by the brightness: s = M / Q {\displaystyle s={\sqrt {M/Q}}} This definition is inspired by experimental work done with the intention of remedying CIECAM97s's poor performance.[11][12] M is proportional to the chroma C (M = CFL0.25), thus the CIECAM02 definition bears some similarity to the CIELUV definition. An important difference is that the CIECAM02 model accounts for the viewing conditions through the parameter FL.[11]

Excitation purity Excitation purity is the relative distance from the white point. Contours of constant purity can be found by shrinking the spectral locus about the white point. The points along the line segment have the same hue, with pe increasing from 0 to 1 between the white point and position on the spectral locus (position of the color on the horseshoe shape in the diagram) or (as at the saturated end of the line shown in the diagram) position on the line of purples. The excitation purity (purity for short) of a stimulus is the difference from the illuminant's white point to the furthest point on the chromaticity diagram with the same hue (dominant wavelength for monochromatic sources); using the CIE 1931 color space:[13] p e = ( x − x n ) 2 + ( y − y n ) 2 ( x I − x n ) 2 + ( y I − y n ) 2 {\displaystyle p_{e}={\sqrt {\frac {(x-x_{n})^{2}+(y-y_{n})^{2}}{(x_{I}-x_{n})^{2}+(y_{I}-y_{n})^{2}}}}} where (xn, yn) is the chromaticity of the white point and (xI, yI) is the point on the perimeter whose line segment to the white point contains the chromaticity of the stimulus. Different color spaces, such as CIELAB or CIELUV may be used, and will yield different results.

Chroma in CIE 1976 L*a*b* and L*u*v* color spaces See also: Psychophysics The naïve definition of saturation does not specify its response function. In the CIE XYZ and RGB color spaces, the saturation is defined in terms of additive color mixing, and has the property of being proportional to any scaling centered at white or the white point illuminant. However, both color spaces are nonlinear in terms of psychovisually perceived color differences. It is also possible—and sometimes desirable—to define a saturation-like quantity that is linearized in term of the psychovisual perception. In the CIE 1976 L*a*b* and L*u*v* color spaces, the unnormalized chroma is the radial component of the cylindrical coordinate CIE L*C*h (lightness, chroma, hue) representation of the L*a*b* and L*u*v* color spaces, also denoted as CIE L*C*h(a*b*)[citation needed] or CIE L*C*h for short, and CIE L*C*h(u*v*). The transformation of (a*, b*) to (C*ab, hab) is given by: C a b ∗ = a ∗ 2 + b ∗ 2 {\displaystyle C_{ab}^{*}={\sqrt {a^{*2}+b^{*2}}}} h a b = arctan ⁡ b ∗ a ∗ {\displaystyle h_{ab}=\arctan {\frac {b^{*}}{a^{*}}}} and analogously for CIE L*C*h(u*v*). The chroma in the CIE L*C*h(a*b*) and CIE L*C*h(u*v*) coordinates has the advantage of being more psychovisually linear, yet they are non-linear in terms of linear component color mixing. And therefore, chroma in CIE 1976 L*a*b* and L*u*v* color spaces is very much different from the traditional sense of "saturation". Chroma in color appearance models Another, psychovisually even more accurate, but also more complex method to obtain or specify the saturation is to use a color appearance model. Here, the chroma color appearance parameter might (depending on the color appearance model) be intertwined with e.g. the physical brightness of the illumination or the characteristics of the emitting/reflecting surface, which is more sensible psychovisually.

References ^ "colourfulness | eilv". eilv.cie.co.at. Archived from the original on 2017-08-06. Retrieved 2017-12-20.  ^ a b c Fairchild, Mark (2013). Color Appearance Models. John Wiley & Sons. , page 87. ^ "CIE e-ILV 17-139". Archived from the original on 2017-04-10.  ^ "CIE e-ILV 17-831". Archived from the original on 2017-04-10.  ^ "The Dimensions of Colour". www.huevaluechroma.com. Archived from the original on 2017-03-30. Retrieved 2017-04-10.  ^ "CIE e-ILV 17-1136". Archived from the original on 2017-04-10.  ^ a b "The Dimensions of Colour". www.huevaluechroma.com. Archived from the original on 2017-03-30. Retrieved 2017-04-10.  ^ Schanda, János (2007). Colorimetry: Understanding the CIE System. Wiley Interscience. ISBN 978-0-470-04904-4. Archived from the original on 2017-01-17. , page 88. ^ Hunt, Robert William Gainer (1993). Leslie D. Stroebel, Richard D. Zakia, ed. The Focal Encyclopedia of Photography. Focal Press. p. 124. ISBN 0-240-51417-3. Archived from the original on 2017-01-17.  ^ Lübbe, Eva (2010). Colours in the Mind - Colour Systems in Reality- A formula for colour saturation. [Book on Demand]. ISBN 978-3-7881-4057-1.  ^ a b Moroney, Nathan; Fairchild, Mark D.; Hunt, Robert W.G.; Li, Changjun; Luo, M. Ronnier; Newman, Todd (November 12, 2002). IS&T/SID Tenth Color Imaging Conference. The CIECAM02 Color Appearance Model (PDF). Scottsdale, Arizona: The Society for Imaging Science and Technology. ISBN 0-89208-241-0.  ^ Juan, Lu-Yin G.; Luo, Ming R. (June 2002). Robert Chung, Allan Rodrigues, eds. Magnitude estimation for scaling saturation. 9th Congress of the International Colour Association. Proceedings of SPIE. 4421. pp. 575–578. doi:10.1117/12.464511. CS1 maint: Uses editors parameter (link) ^ Stroebel, Leslie D.; Zakia, Richard D. (1993). The Focal Encyclopedia of Photography (3E ed.). Focal Press. p. 121. ISBN 0-240-51417-3. Archived from the original on 2017-01-17.  v t e Color topics Red Orange Yellow Green Cyan Blue Indigo Violet Purple Magenta Pink Brown White Gray Black Color science Color physics Electromagnetic spectrum Light Rainbow Visible Spectral colors Chromophore Structural coloration Animal coloration On Vision and Colors Metamerism Spectral power distribution Color perception Color vision Color blindness Achromatopsia test Tetrachromacy Color constancy Color term Color depth Color photography Spot color Color printing Web colors Color mapping Color code Color management Chrominance False color Chroma key Color balance Color cast Color temperature Eigengrau Color psychology Color symbolism Color preferences Lüscher color test Kruithof curve Political color National colors Chromophobia Chromotherapy Color philosophy Color space Color model additive subtractive Color mixing Primary color Secondary color Tertiary color (intermediate) Quaternary color Quinary color Aggressive color (warm) Receding color (cool) Pastel colors Color gradient Color scheme Color tool Monochromatic colors Complementary colors Analogous colors Achromatic colors (Neutral) Polychromatic colors Impossible colors Light-on-dark Tinctures in heraldry Color theory Chromaticity diagram Color solid Color wheel Color triangle Color analysis (art) Color realism (art style) Color terms Basic terms Blue Green Red Yellow Pink Purple Orange Black Gray White Brown Cultural differences Linguistic relativity and the color naming debate Blue–green distinction in language Color history Color in Chinese culture Traditional colors of Japan Human skin color Color dimensions Hue Dichromatism Colorfulness (chroma and saturation) Tints and shades Lightness (tone and value) Grayscale Color organizations Pantone Color Marketing Group The Color Association of the United States International Colour Authority International Commission on Illumination (CIE) International Color Consortium International Colour Association Lists List of colors: A–F List of colors: G–M List of colors: N–Z List of colors (compact) List of colors by shade List of color palettes List of color spaces List of Crayola crayon colors history pencil colors marker colors Color chart List of fictional colors List of RAL colors List of web colors Related Vision Image processing Multi-primary color display Quattron Qualia Lighting Local color (visual art) Category Portal Index of color-related articles Retrieved from "https://en.wikipedia.org/w/index.php?title=Colorfulness&oldid=816381179" Categories: ColorHidden categories: CS1 maint: Uses editors parameterArticles needing expert attention from December 2011All articles needing expert attentionColor articles needing expert attentionAll articles with unsourced statementsArticles with unsourced statements from October 2014Articles with unsourced statements from January 2011