RGB spectrum

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This spectrum type is designed mainly for material properties such as albedo, reflection color... It allows adjusting material properties with RGB values as in traditional computer graphic software.

The generated spectrum has the following properties:

  • Exact matching of RGB values with D65 illuminant, CIE 1931 2° observer, and conversion to standard sRGB primaries.
  • Natural smooth and continuous spectrum with no discontinuities or sharp peaks
  • If R, G and B are equal, then the spectrum is uniform.
  • The spectrum values are always higher than min(R,G,B) and lower than max(R,G,B).
  • More specifically, if R,G and B are within [0,1], the spectrum values also. This ensures physically plausible values, for instance used as albedo spectrum.
  • The spectrum continuously dependent of R,G and B.

If no gamma value is specified, the values are considered as physical linear coefficients (gamma=1.0). RGB values used in desktop and 3D software use a gamma of 2.2. RGB values in image files are also often encoded with a gamma of 2.2.


This spectrum type has no intrinsic unit. It takes the same unit as R, G and B. It is mostly used with no unit, when RGB values correspond to an albedo, reflection or transmission color.


Red, green and blue values
The gamma value

See also

Spectrum types