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| {{other uses|Lightness (disambiguation)}}
| | The name of the writer is Nestor. Delaware has usually been my residing location and will by no means move. The thing she adores most is to play handball but she can't make it her occupation. Interviewing is what she does but soon she'll be on her personal.<br><br>my blog post: [http://ssdpro.Com.ng/web/index.php?do=/GreggMaitland/blog/improve-your-auto-repair-knowledge-with-this-particular-advice/ extended auto warranty] |
| [[Image:ColorValue.svg|frame|right|Three [[hue]]s in the [[Munsell color system|Munsell color model]]. Each color differs in value from top to bottom in equal perception steps. The right column undergoes a dramatic change in perceived color.]]
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| '''Lightness''' (sometimes called '''value''' or '''tone''') is a property of a [[color]], or a dimension of a [[color space]], that is defined in a way to reflect the subjective brightness perception of a color for humans along a lightness–darkness axis.
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| Various [[color models]] have an explicit term for this property. The [[Munsell color system|Munsell color model]] uses the term ''value'', while the [[HSL and HSV|HSL color model]] and [[Lab color space]] use the term ''lightness''. The [[HSL and HSV|HSV model]] uses the term ''value'' a little differently: a color with a low value is nearly black, but one with a high value is the pure, fully saturated color.
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| In [[subtractive color]] (i.e. paints) value changes can be achieved by adding black or white to the color. However, this also reduces saturation. [[Chiaroscuro]] and [[Tenebrism]] both take advantage of dramatic contrasts of value to heighten drama in art. Artists may also employ [[shading]], subtle manipulation of value.
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| ==Relationship between lightness, value, and luminance==
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| The [[Munsell]] [[value (colorimetry)|value]] has long been used as a [[perceptually uniform]] lightness scale. A question of interest is the relationship between the Munsell value scale and the [[luminance (relative)|relative luminance]]. Aware of the [[Weber–Fechner law]], Munsell remarked "Should we use a logarithmic curve or curve of squares?"<ref>{{cite journal|title=The early development of the Munsell system|first=Rolf G.|last=Kuehni|volume=27|issue=1|pages=20–27|doi=10.1002/col.10002|date=February 2002|journal=Color Research & Application}}</ref> Neither option turned out to be quite correct; scientists eventually converged on a roughly cube-root curve, consistent with the [[Stevens power law]] for brightness perception, reflecting the fact that lightness is proportional to the number of nerve impulses per nerve fiber per unit time.<ref>{{cite journal|title=Light Energy and Brightness Sensation|first=Robert W. G.|last=Hunt|date=May 18, 1957|page=1026|volume=179|issue=4568| journal=Nature|doi=10.1038/1791026a0}}</ref> The remainder of this section is a chronology of lightness approximations, leading to CIELAB.
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| ''Note'': Munsell's V runs from 0 to 10, while Y typically runs from 0 to 100 (often interpreted as a percentage). Typically, the relative luminance is normalized so that the "reference white" (say, [[magnesium oxide]]) has a tristimulus value of Y=100. Since the reflectance of magnesium oxide (MgO) relative to the [[diffuser (optics)#Perfect reflecting diffuser|perfect reflecting diffuser]] is 97.5%, V=10 corresponds to Y=100/97.5%≈102.6 if MgO is used as the reference.<ref>{{cite book| url=http://books.google.com/?id=hNDS1C6x0WYC&pg=PA200&dq=0.975+OR+97.5+%22magnesium+oxide%22|title=Light Vision Color|first=Arne|last=Valberg|publisher=John Wiley and Sons|year=2006|isbn=0470849029|page=200}}</ref> | |
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| [[Image:Lightness approximations.svg|thumb|right|500px|Observe that the lightness is 50% for a luminance of around 18% relative to the reference white.]]
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| ;1920 : Priest ''et al.'' provide a basic estimate of the Munsell value (with Y running from 0 to 1 in this case):<ref>{{Cite journal|first=Irwin G.|last=Priest|last2=Gibson|first2=K.S.|last3=McNicholas|first3=H.J.|title=An examination of the Munsell color system. I: Spectral and total reflection and the Munsell scale of Value|series=Technical paper 167|page=27|issue=3|publisher=United States Bureau of Standards|date=September 1920|postscript=<!--None-->}}</ref>
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| :<math>V=10 \sqrt{Y}</math>
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| ;1933 : Munsell, Sloan, and Godlove launch a study on the Munsell neutral value scale, considering several proposals relating the relative luminance to the Munsell value, and suggest:<ref>{{cite journal|first=A.E.O.|last=Munsell|coauthors=Sloan, L.L.; Godlove, I.H.|title=Neutral value scales. I. Munsell neutral value scale|volume=23|issue=11|pages=394–411|date=November 1933|journal=[[JOSA]]| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-23-11-394|doi=10.1364/JOSA.23.000394}} ''Note:'' This paper contains a historical survey stretching to 1760.</ref><ref>{{cite journal|first=A.E.O.|last=Munsell|coauthors=Sloan, L.L.; Godlove, I.H.|journal=[[JOSA]]|title=Neutral value scales. II. A comparison of results and equations describing value scales|volume=23|date=December 1933|issue=12|pages=419–425| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-23-12-419|doi=10.1364/JOSA.23.000419}}</ref>
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| :<math>V^2=1.4742Y-0.004743Y^2</math>
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| ;1943 : Newhall, Nickerson, and Judd prepare a report for the [[Optical Society of America]]. They suggest a quintic parabola (relating the reflectance in terms of the value):<ref>{{cite journal|year=1943|month=May|title=Final report of the O.S.A. subcommittee on the spacing of the Munsell colors|volume=33|issue=7|pages=385–418|last=Newhall|first=Sidney M.|coauthors=Nickerson, Dorothy; Judd, Deane B| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-33-7-385|doi=10.1364/JOSA.33.000385|journal=Journal of the Optical Society of America}}</ref>
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| :<math>Y=1.2219V-0.23111V^2+0.23951V^3-0.021009V^4+0.0008404V^5</math>
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| ;1943 : Using Table II of the O.S.A. report, Moon and Spencer express the value in terms of the luminance:<ref>{{cite journal|journal=[[JOSA]]|title=Metric based on the composite color stimulus|first=Parry|last=Moon|coauthors=Spencer, Domina Eberle|volume=33|issue=5|date=May 1943|pages=270–277|url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-33-5-270|doi=10.1364/JOSA.33.000270}}</ref>
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| :<math>V=5 (Y/19.77)^{0.426}=1.4 Y^{0.426}</math>
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| ;1944 : Saunderson and Milner introduce a subtractive constant in the previous expression, for a better fit to the Munsell value.<ref>{{cite journal|journal=[[JOSA]]|title=Further study of ω space|last=Saunderson|first=Jason L.|coauthors=Milner, B.I.|volume=34|issue=3|pages=167–173|date=March 1944| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-34-3-167|doi=10.1364/JOSA.34.000167}}</ref> Later, [[Dorothea Jameson|Jameson]] and Hurvich claim that this corrects for simultaneous [[contrast effect]]s.<ref>{{cite journal|first=Leo M.|last=Hurvich|coauthors= Jameson, Dorothea|title=An Opponent-Process Theory of Color Vision|journal=[[Psychological Review]]|pages=384–404|date=November 1957|volume=64|issue=6|pmid=13505974|url=http://psycnet.apa.org/index.cfm?fa=buy.optionToBuy&id=1959-02846-001|doi=10.1037/h0041403}}</ref><ref>{{cite journal|first=Dorothea|last=Jameson|coauthors=Leo M., Hurvich|title=Theory of brightness and color contrast in human vision|journal=Vision Research|date=May 1964|volume=4|issue=1-2|pmid=5888593|pages=135–154|doi=10.1016/0042-6989(64)90037-9}}</ref>
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| :<math>V=2.357 Y^{0.343}-1.52</math>
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| ;1955 : Ladd and Pinney of [[Eastman Kodak]] are interested in the Munsell value as a perceptually uniform lightness scale for use in [[television]]. After considering one logarithmic and five [[power-law]] functions (per [[Stevens' power law]]), they relate value to reflectance by raising the reflectance to the power of 0.352:<ref>{{cite journal|title=Empirical relationships with the Munsell Value scale|last=Ladd|first=J.H.|coauthors=Pinney, J.E.|journal=Proceedings of the [[Institute of Radio Engineers]]|volume=43|issue=9|page=1137|date=September 1955|doi=10.1109/JRPROC.1955.277892| url=http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=4055542&arnumber=4055558}}</ref>
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| :<math>V=2.217 Y^{0.352}-1.324</math>
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| :Realizing this is quite close to the cube root, they simplify it to:
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| :<math>V=2.468 Y^{1/3}-1.636</math>
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| ;1958 : Glasser ''et al.'' define the lightness as ten times the Munsell value (so that the lightness ranges from 0 to 100):<ref>{{cite journal|title=Cube-root color coordinate system|first=L.G.|last=Glasser|coauthors=A.H. McKinney, C.D. Reilly, and P.D. Schnelle|journal=[[JOSA]]|volume=48|issue=10|pages=736–740|date=October 1958| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-48-10-736|doi=10.1364/JOSA.48.000736}}</ref>
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| :<math>L^*=25.29 Y^{1/3} - 18.38</math>
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| ;1964 : Wyszecki simplifies this to:<ref name=gunter>{{cite journal|first=Günther|last=Wyszecki|title=Proposal for a New Color-Difference Formula|pages=1318–1319|date=November 1963|volume=53|journal=[[JOSA]]| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-53-11-1314|doi=10.1364/JOSA.53.001318|issue=11}} ''Note:'' The asterisks are not used in the paper.</ref>
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| :<math>W^*=25Y^{1/3}-17</math>
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| :This formula approximates the Munsell value function for <math>1% < Y < 98%</math> (it is not applicable for Y<1%) and is used for the [[CIE 1964 color space]].
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| ;1976 : [[CIELAB]] uses the following formula:
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| :<math>L^* = 116 (Y/Y_n)^{1/3}-16</math>
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| :where <math>Y_n</math> is the Y tristimulus value of a "specified white object" and is subject to the restriction <math>Y/Y_n > 0.01</math>. Pauli removes this restriction by computing a [[linear extrapolation]] which maps Y/Y<sub>n</sub>=0 to L<sup>*</sup>=0 and is tangent to the formula above at the point at which the linear extension takes effect. First, the transition point is determined to be <math>Y/Y_n=(6/29)^3 \approx 0.008856</math>, then the slope of <math>(29/3)^3 \approx 903.3</math> is computed. This gives the two-part function:<ref>{{cite journal|first=Hartmut K.A.|last=Pauli|title=Proposed extension of the CIE recommendation on "Uniform color spaces, color spaces, and color-difference equations, and metric color terms"|journal=[[JOSA]]|volume=66|issue=8|pages=866–867|year=1976| url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-66-8-866|doi=10.1364/JOSA.66.000866}}</ref>
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| :<math>f(u)= \left\{\begin{array}{ll}\frac{841}{108}u + \frac{4}{29}, & u \le (6/29)^3 \\ \\
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| u^{1/3}, & u > (6/29)^3\end{array}\right.</math>
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| :The lightness is then <math>L^*=116 f(Y/Y_n)-16</math>.
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| {{-}}
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| At first glance, you might approximate the lightness function by a cube root, an approximation that is found in much of the technical literature. However, the linear segment near black is significant. The best-fit pure power function has an exponent of about 0.42, far from 1/3.{{citation needed|date=December 2013}}
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| An approximately 18% grey card, having an exact reflectance of <math>\left(33/58\right)^3</math>, has a lightness value of 50. It is called "mid grey" because its lightness is midway between black and white.
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| == Other psychological effects ==
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| This subjective perception of luminance in a non-linear fashion is one thing that makes gamma compression of images worthwhile. Beside this phenomenon there are other effects involving perception of lightness. Chromacity can affect perceived lightness as described by the [[Helmholtz–Kohlrausch effect]]. Though the CIE L*a*b* space and relatives do not account for this effect on lightness, it may be implied in the Munsell color model.
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| Light levels may also affect perceived chromacity, as with the [[Purkinje effect]].
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| == See also ==
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| * [[Brightness]]
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| * [[Tints and shades]]
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| ==References==
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| {{Reflist}}
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| {{Color topics}}
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| [[Category:Color]]
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| [[Category:Photometry]]
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| [[Category:Vision]]
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| [[ar:إضاءة اللون]]
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| [[be-x-old:Сьвятлыня]]
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| [[fr:Clarté (colorimétrie)]]
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| [[ja:バルール]]
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| [[no:Valør]]
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| [[no:Lyshet]]
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| [[pt:Luminosidade (cor)]]
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| [[ru:Светлота (цвет)]]
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The name of the writer is Nestor. Delaware has usually been my residing location and will by no means move. The thing she adores most is to play handball but she can't make it her occupation. Interviewing is what she does but soon she'll be on her personal.
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