Luminance Icon

asLuminance

A node that returns the luminance of a color, respecting the color space definitions (that is, the chromaticity coordinates of the primaries and the white point).


Parameters


Color Attributes

Input Color
The color being evaluated

Color Space

Derive From Maya CMS
Uses the render space definitions from Maya’s synColor. This will set the chromaticity coordinates of the RGB primaries, and the white point, standardized in the color space chosen in the synColor configuration. When this is not set, the user must set the appropriate options matching its choice of rendering/working space.

Important

appleseed and appleseed-maya don’t yet take OpenColorIO into account, so this parameter considers the working space definitions from synColor only. If you wish to use OCIO you must set the appropriate color space and white point settings. The default is (scene-linear) sRGB/Rec.709 primaries, with D65 whitepoint.

Input Color Space

The color space chosen as render/working space. It allows the user to choose one of the following

Hint

When choosing Chromaticity Coordinates, the user must enter the xy chromaticity coordinates of the R,G,B primaries, and must choose the whitepoint, either in the form of one of the available standard illuminants, in the xy chromacity coordinates of the whitepoint, or via the correlated color temperature.

R xy Coordinates
The xy chromaticity coordinates of the red primary.
G xy Coordinates
The xy chromaticity coordinates of the green primary.
B xy Coordinates
The xy chromaticity coordinates of the blue primary.
White Point

The white point definition, which can be one of the following options:

  • Standard Illuminant D50
  • Standard Illuminant D55
  • Standard Illuminant D60
  • Standard Illuminant D65
  • Standard Illuminant D75
  • DCI White Point
  • White Point E
  • Correlated Color Temperature
  • White Point Chromaticity Coordinates
Color Temperature
The input color temperature value in Kelvin degrees, from 1667K to 25000K.
W xy Coordinates
The xy chromacity coordinates of the white point.

Outputs

Result
The luminance of the input color.

Screenshots

Some examples of the output luminance of the input color ramp, rendered in (scene linear) Rec.709 space, standard illuminant D65, with different color spaces and whitepoints chosen. The mismatches in color spaces are for illustration purposes. If the settings cannot be derived automatically from your DCC application, then the choice of color space should match your choice or render/working space.


References

[DFD+15]Haarm-Pieter Duiker, Alexander Forsythe, Scott Dyer, Ray Feeney, Will McCown, Jim Houston, Andy Maltz, and Doug Walker. Acescg: a common color encoding for visual effects applications. In Proceedings of the 2015 Symposium on Digital Production, DigiPro ‘15, 53–53. New York, NY, USA, 2015. ACM. URL: http://doi.acm.org/10.1145/2791261.2791273, doi:10.1145/2791261.2791273.
[Ini11]Digital Cinema Initiatives. Rp 431-2:2011 - smpte recommended practice - d-cinema quality #x2014; reference projector and environment. SMPTE RP 431-2:2011, pages 1–14, April 2011. doi:10.5594/SMPTE.RP431-2.2011.
[oMPAS12]The Academy of Motion Picture Arts and Sciences. St 2065-1:2012 - smpte standard - academy color encoding specification (aces). ST 2065-1:2012, pages 1–23, April 2012. doi:10.5594/SMPTE.ST2065-1.2012.
[SCW14]M. Sugawara, S. Y. Choi, and D. Wood. Ultra-high-definition television (rec. itu-r bt.2020): a generational leap in the evolution of television [standards in a nutshell]. IEEE Signal Processing Magazine, 31(3):170–174, May 2014. doi:10.1109/MSP.2014.2302331.