Editing HSL and HSV (section)

===Color-making attributes===
{{see also|Color vision}}
The dimensions of the HSL and HSV geometries – simple transformations of the not-perceptually-based RGB model – are not directly related to the [[photometry (optics)|photometric]] color-making attributes of the same names, as defined by scientists such as the [[International Commission on Illumination|CIE]] or [[ASTM International|ASTM]]. Nonetheless, it is worth reviewing those definitions before leaping into the derivation of our models.{{refn|group=upper-alpha |"Clearly, if color appearance is to be described in a systematic, mathematical way, definitions of the phenomena being described need to be precise and universally agreed upon."<ref name=Fairchild-term>[[#Fairchild|Fairchild (2005)]], [https://books.google.com/books?id=8_TxzK2B-5MC&pg=PT106 {{nobr|pp. 83–93}}]</ref>}} For the definitions of color-making attributes which follow, see:<ref name=Fairchild-term/><ref name=Kuehni>[[#Kuehni|Kuehni (2003)]]</ref><ref>{{cite book |publisher=[[ASTM International|ASTM]] |date=2009 |url=http://www.astm.org/Standards/E284.htm |title=Standard Terminology of Appearance E284}}</ref><ref>{{cite book |publisher=[[International Commission on Illumination|CIE]] and [[International Electrotechnical Commission|IEC]] |date=1987 |url=http://www.cie.co.at/publ/abst/17-4-89.html |title=International Lighting Vocabulary |edition=4th |isbn=978-3-900734-07-7 |access-date=2010-02-05 |archive-url=https://web.archive.org/web/20100227034508/http://www.cie.co.at/publ/abst/17-4-89.html |archive-date=2010-02-27 |url-status=dead }}</ref><ref name=Poynton>[[#Poynton|Poynton (1997)]]</ref><ref>{{cite book |title=Digital Color Imaging Handbook |last=Sharma |first=G.|year=2003 |publisher=CRC Press |location=Boca Raton, FL |isbn=978-0-8493-0900-7 }}</ref>

; [[Hue]]: The "attribute of a visual sensation according to which an area appears to be similar to one of the [[unique hues|perceived colors]]: red, yellow, green, and blue, or to a combination of two of them".<ref name=Fairchild-term/>
; [[Radiance]] (''L''<sub>e,Ω</sub>): The [[Radiant flux|radiant power]] of light passing through a particular surface per unit [[solid angle]] per unit projected area, measured in [[International System of Units|SI units]] in [[watt]] per [[steradian]] per [[square metre]] ({{nobreak|W·sr<sup>−1</sup>·m<sup>−2</sup>}}).
; [[Luminance]] (''Y'' or ''L''<sub>v,Ω</sub>): The radiance weighted by the effect of each wavelength on a typical human observer, measured in SI units in [[candela per square metre|candela per square meter]] ({{nobreak|cd/m<sup>2</sup>}}). Often the term ''luminance'' is used for the [[relative luminance]], ''Y''/''Y''<sub>''n''</sub>, where ''Y''<sub>''n''</sub> is the luminance of the reference [[white point]].
; [[Luma (video)|Luma]] (''{{prime|Y}}''): The weighted sum of [[gamma correction|gamma-corrected]] {{nobr|''{{prime|R}}''}}, {{nobr|''{{prime|G}}''}}, and {{nobr|''{{prime|B}}''}} values, and used in [[YCbCr|{{nobr|Y{{prime}}CbCr}}]], for [[JPEG]] compression and video transmission.
; [[Brightness|Brightness (or value)]]: The "attribute of a visual sensation according to which an area appears to emit more or less light".<ref name=Fairchild-term/>
; [[Lightness (color)|Lightness]]: The "brightness relative to the brightness of a similarly illuminated white".<ref name=Fairchild-term/>
; [[Colorfulness]]: The "attribute of a visual sensation according to which the perceived color of an area appears to be more or less chromatic".<ref name=Fairchild-term/>
; [[Chrominance|Chroma]]: The "colorfulness relative to the brightness of a similarly illuminated white".<ref name=Fairchild-term/>
; [[Colorfulness#Saturation|Saturation]]: The "colorfulness of a stimulus relative to its own brightness".<ref name=Fairchild-term/>

''Brightness'' and ''colorfulness'' are absolute measures, which usually describe the [[spectral power distribution|spectral distribution]] of light entering the eye, while ''lightness'' and ''chroma'' are measured relative to some white point, and are thus often used for descriptions of surface colors, remaining roughly constant even as brightness and colorfulness change with different [[computer graphics lighting|illumination]]. ''Saturation'' can be defined as either the ratio of colorfulness to brightness, or that of chroma to lightness.