On Delta UV computation?

[blue-j]

Is this legit?

https://www.waveformlighting.com/tech/calculate-duv-from-cie-1931-xy-coordinates

No citation for the calculation is provided. Does Colour-science have this? I could not find it in the API reference.

Thanks in advance for any consideration you provide this post!

• J

[tjdcs]

We don't have this particular calculation, but that's ok because it's just an approximation function anyway. It's more accurate to do the correct conversions.

Convert from xy to UCS uv, and then compute uv to CCT with the defaut options.

from colour import xy_to_UCS_uv, uv_to_CCT

cct_duv = uv_to_CCT(xy_to_UCS_uv((0.3143, 0.3275)))
print(f"CCT: {cct_duv[0]:.1f}, ∆uv: {cct_duv[1]:.4f}")

[blue-j]

You're kind to share your knowledge, thank you! :) Is there any reason to calculate Duv for red primary for example? Is this really only about white? I can't see how someone would care about the distance to the Planckian locus for a red point, but I want to be thorough in what I provide our users.

[KelSolaar]

You could compute it for any value but the concept of CCT is only valid within 0.05 Duv

[blue-j]

for RGB color spaces, does CCT = illuminant in K? it seems to.

[KelSolaar]

CCT stands for Correlated Colour Temperature, i.e. Colour Temperature related to a blackbody with an offset normal to the blackbody locus.