994:(gamma encoded) R′G′B′ components, where in some implementations the weighting coefficients are applied to the gamma encoded signal. Also, in many instances, for technical reasons the weighting coefficients are not identical to those coefficients that naturally follow from the primaries and the white point; for example PAL SDTV signals, and also NTSC signals as specified since 1987, use weighting coefficients that were natural for the primaries of the original 1953 NTSC standard (mixing the three defined 1953 NTSC primaries in the proportions given by the weighting coefficients results in the defined 1953 NTSC white) but which aren’t the natural ones to use for their own specified primaries. In those cases, luma will not purely be a function of gamma-corrected brightness (however defined) but also depends to some extent on the hue and saturation of the color. Some colorspaces that use luma include
1914:
32:
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Different linear coefficients are needed to determine luminance for a given colorspace, which are calculated from their primary chromaticities (defined by their x&y or uʹ&vʹ chromaticity coordinates). For RGB spaces that use real colors for primaries, these coefficients will be positive for
250:
The use of relative values is useful in color or appearance models that describe perception relative to the eye's adaptation state and a reference white. For example, in prepress for print media, the absolute luminance of light reflecting off the print depends on the specific illumination, but a
803:
656:) are both linear to changes in the volume of light. Conversions from color spaces where light or lightness are encoded with a power curve, such as most image and video formats, must be linearized before being transformed to Y or the XYZ space.
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the conversion into XYZ space, but may be negative for transforming back to RGB. The green coefficient is normally the largest and blue normally smallest, and normally form the middle row of the RGB-to-XYZ color transformation matrix.
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For nonlinear gamma-compressed R′G′B′ color spaces as typically used for computer images, a linearization of the R′G′B′ components to RGB is needed before the linear combination.
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The simple method is to apply the inverse power curve to each of the color channels, as an example for several common RGB color spaces, a 2.2 power curve is applied:
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as "green" light is the major component of luminance, responsible for the majority of light perceived by humans, and "blue" light the smallest component.
208:. Like the photometric definition, it is related to the luminous flux density in a particular direction, which is radiant flux density weighted by the
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can then be calculated for these colorspaces by using the coefficients for the Y component of the transform matrix. For instance, for
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must be used with the subcomponents to create the gamma encoded R′G′B′ components, which are then linearized to RGB by inverting the
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is intended to be linear to human perception of lightness/darkness, and since human perception of light is non-linear,
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values are normalized as 0.0 to 1.0 (or 1 to 100), with 1.0 (or 100) being a theoretical perfect reflector of 100%
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798:{\displaystyle R_{lin}={R^{\prime }}^{2.2}\ \ G_{lin}={G^{\prime }}^{2.2}\ \ B_{lin}={B^{\prime }}^{2.2}}
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is linear to light, but human perception has a non-linear response to lightness/darkness/brightness.
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both of which use the same primaries and whitepoint, relative luminance can be calculated from
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using relative luminance can predict the appearance by referencing the given light source.
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602:{\displaystyle \ \ Y_{scale_{100}}={L_{stimulus} \over L_{max}}\ \times \ 100}
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refers to relative luminance. If the maximum luminance for a given example is
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including spectral weighting for human vision, but while luminance
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934:{\displaystyle Y=0.2126*R_{lin}+0.7152*G_{lin}+0.0722*B_{lin}}
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For the vision capacities of organisms or machines, see
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convert the gamma-compressed RGB values to linear RGB
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1126:(also known as "Lstar" and not to be confused with
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may be too technical for most readers to understand
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613:Relative luminance and "gamma encoded" colorspaces
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480:{\displaystyle Y={L_{stimulus} \over L_{ref}}\ \ }
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1262:Digital Video and HDTV: Algorithms and Interfaces
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958:Relative luminance should not be confused with
1200:is a nonlinear function of relative luminance
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1294:(6 ed.). Item 3.2: ITU. 2015. p. 3
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259:Relative luminance and colorimetric spaces
240:{\displaystyle {\overline {y}}(\lambda )}
69:Learn how and when to remove this message
53:, without removing the technical details.
1061:Relative luminance and perceptual spaces
1006:. To determine relative luminance, The
146:is a measure of light in units such as
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990:(Y prime), which is a weighted sum of
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51:make it understandable to non-experts
105:photometric definition of luminance
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16:Ratiometric definition of luminance
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404:then the relative luminance is
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1359:A Field Guide to Digital Color
1346:
1320:
1279:
1252:
247:of the CIE Standard Observer.
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228:
1:
1245:
946:luminous efficiency function
397:{\displaystyle L_{stimulus}}
223:
210:luminous efficiency function
7:
1223:
1026:{\displaystyle Y^{\prime }}
983:{\displaystyle Y^{\prime }}
10:
1965:
1825:Colour Index International
21:Luminance (disambiguation)
18:
1949:Film and video technology
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1259:Poynton, Charles (2003).
944:The formula reflects the
1312:: CS1 maint: location (
1122:component is perceptual
177:{\displaystyle cd/m^{2}}
1288:ITU Parameters for HDTV
349:{\displaystyle L_{ref}}
316:{\displaystyle L_{max}}
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1193:{\displaystyle L^{*}}
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1166:{\displaystyle L^{*}}
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1115:{\displaystyle L^{*}}
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1842:Federal Standard 595
1422:List of color spaces
1235:CIE 1931 color space
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19:For other uses, see
1362:. A K Peters, Ltd.
1265:. Morgan Kaufmann.
82:Relative luminance
1329:"RGB/XYZ Matrices"
1327:Lindbloom, Bruce.
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1213:{\displaystyle Y}
1139:{\displaystyle L}
1077:{\displaystyle Y}
1050:{\displaystyle Y}
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649:{\displaystyle L}
629:{\displaystyle Y}
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283:{\displaystyle Y}
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197:{\displaystyle Y}
139:{\displaystyle L}
118:{\displaystyle L}
95:{\displaystyle Y}
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1531:RGB color spaces
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1757:Imaginary color
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1576:SMPTE 240M/"C"
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1806:Color systems
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1503:CIELUV (1976)
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1498:CIELAB (1976)
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39:This article
37:
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1919:Color vision
1427:Color models
1358:
1348:
1336:. Retrieved
1332:
1322:
1296:. Retrieved
1287:
1281:
1261:
1254:
1240:Chromaticity
1146:luminance).
1086:
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959:
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950:
943:
843:, and then
829:ITU-R BT.709
807:
658:
616:
488:
262:
249:
103:follows the
81:
80:
65:
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40:
1897: [
1852:ICC profile
1411:Color space
1095:space, the
265:colorspaces
1944:Photometry
1933:Categories
1742:Hexachrome
1551:Wide-gamut
1493:UVW (1964)
1488:YUV (1960)
1483:RGB (1931)
1478:XYZ (1931)
1246:References
1894:JIS Z8102
1677:Rec. 2100
1665:Rec. 2100
1660:Rec. 2020
1591:Rec. 2100
1586:Rec. 2020
1338:9 October
1308:cite book
1298:9 October
1230:Luminance
1186:∗
1159:∗
1124:lightness
1108:∗
1019:′
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863:∗
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591:×
232:λ
224:¯
59:June 2020
1857:ISCC–NBS
1747:HSL, HSV
1732:Coloroid
1727:ColorADD
1655:Rec. 709
1650:Rec. 601
1581:Rec. 709
1571:Rec. 601
1556:ProPhoto
1513:CIECAM16
1508:CIECAM02
1460:CIECAM16
1445:CIECAM02
1356:(2003).
1224:See also
263:For CIE
1877:Pantone
1872:Ostwald
1862:Munsell
1767:OSA-UCS
45:Please
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1717:CcMmYK
1566:DCI-P3
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1093:L*u*v*
1089:L*a*b*
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1002:, and
910:0.0722
885:0.7152
860:0.2126
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1939:Color
1901:]
1762:Oklab
1710:Other
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1672:ICtCp
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1626:SECAM
1621:YDbDr
1561:scRGB
1546:Adobe
1455:CAM16
1292:(PDF)
636:(and
1887:list
1820:ANPA
1815:ACES
1772:PCCS
1722:CMYK
1638:NTSC
1601:Y′UV
1536:sRGB
1450:iCAM
1364:ISBN
1340:2021
1314:link
1300:2021
1267:ISBN
1091:and
1087:For
1000:Y′IQ
996:Y′UV
961:luma
833:sRGB
831:and
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1787:HWB
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1752:HCL
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1609:YUV
1523:RGB
1470:CIE
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791:2.2
747:2.2
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1777:RG
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