For the CIE1931 XYZ tristimulus values and x y chromaticity coordinates, I think these are unitless quantities. I have checked different plots of these quantities and haven't seen their units labeled, but could you please confirm that they are unitless?

  • I assume that you are talking about Lab colour space, in which case your assumption is correct, no units.
    – Westside
    Jan 17, 2017 at 14:15
  • @Chris hes talking of XYZ that is similar but different from Lab.
    – joojaa
    Jan 17, 2017 at 14:18
  • Clarified the question, sorry
    – KAE
    Jan 17, 2017 at 14:46
  • Found a related article here, onlinelibrary.wiley.com/doi/10.1002/col.5080210404/abstract
    – KAE
    Jan 18, 2017 at 13:54

1 Answer 1


XYZ measures the perecieved input of a human, not a physical quantity. So yes the data does not really have a unit as such. Mainly because there are so many variables such as what part of the eye was used to observe the color. Secondly because there is no unit for a intensity distribution of light. So its more like asking for a unit for a shape of a car which can not be described by a simple description.

  • Ps: Color science is not the same as color theory. Color science overexceeds the realm of graphic design so theis is on the edge of belonging on computer graphics stackexhange since that site is meant for researchers in science which includes color science.
    – joojaa
    Jan 17, 2017 at 14:36

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