Color: The Limits of a ‘Standard’ Observer

"Imagine you adjust two separate color-tunable LED fixtures to visually match in color appearance, but when you pull out your expensive, accurate spectroradiometer and measure the chromaticity of each, there is a significant difference that should be noticeable. How can that be?

Alternatively, you tune two LED fixtures to be a perfect chromaticity match, according to that meter. Then, you show them to everyone in your office. Chaos ensues when the team realizes they are not a visual match for most of the group despite what the meter says."

www.ies.org/lda-magazine/featured-content/color-the-limits-of-a-standard-observer/

Iliah…awesome to see you here!

1931 observer works reasonably well, true. For what I'm doing for reproduction, 1964 observer worked better, but I was forced to convert to 1931 observer for RGB output (this is a general problem that prevented many from using 1964 observer). Luckily, most of my production output is CMYK. 2015 observer is much less prone to metameric error, especially blue <-> purple, but if the working RGB spaces don't support it, IMHO it is destined to very narrow use (textile / paint / pigment / light colour matching, mostly).

And back to you ;)

The reason why I tend to use the 1931 Observer is that most easily available standard color space data (e.g. white points, conversion matrices, etc.) are for it; and for compatibility with the vast majority of software in use today.

Also anecdotally, when determining Forward Matrices by minimizing color differences with a standard target like a ColorChecker24, I get better mean dE2000 residual errors with the 1931 Observer than with 2015's. I haven't investigated why - but perhaps dE2000 expects 1931-referred data?

Jack

Hi, Jack
Lab is 1931-referenced, right. Also, how do you obtain reference XYZ values?

Hey Iliah, in those cases I try to do everything starting from spectral data. Here is the relative Matlab routine, hope it is self explanatory.

function o = computeRef(o)
      %compute illuminant white point and target xyz/lab reference values referred to it.  All energy units.

      o.xyzn = o.illSpectrum * o.cmf;                           %white point of chosen illuminant

      o.cc24irradiance = o.cc24reflectance .* o.illSpectrum;
      o.xyzRef = o.cc24irradiance * o.cmf;                  %cc24 xyz reference values
      o.labRef = xyz2labn(o.xyzRef,o.xyzn);               %cc24 lab reference values

      o.xyzRef = o.xyzRef / o.xyzn(2);                         %normalize to Y
      o.xyzn = o.xyzn / o.xyzn(2);                                %normalize white point

      [o.cctRef,o.tintRef] = cctDuv(o.xyzn);                 %CCT and Tint of reference white
end

I suspect dE2000 internal parameters to be fine tuned to the 1931 Observer.

Right on both accounts, start from spectra and dE00 is for 1931 observer; also LCH from Lab not referenced to 1931 is a nightmare, Duv too.
Good ideas in 2015, but very limited workflow, IMO not ready for practical use for general colour management, but at least they tell what CMFs to use.
Maybe this will be of some help:
files.cie.co.at/LpR%2060%20CIE%20RESEARCH%20Special%20-%20Cone-Fundamental-Based%20CIE%20Colorimetry.pdf
colour.readthedocs.io/en/develop/_modules/colour/colorimetry/transformations.html

Is that something they imagined or something they actually experienced?

BTW, this forum is hiding in an obscure corner of this site, hard to find.

++++
The poster formerly known as J A C S.

It's what happens, especially with wide gamut devices. That's the selling point of Minolta CA-410 colour analyzer.
Edit: sensing.konicaminolta.asia/wp-content/uploads/2018/09/Resolving_Display_Color_Matching_Issue.pdf

ChatGPT misses the point.:

That was a rhetorical question, and the answer seems to be that they imagined it, as they said. A more serious article, coauthored by three specialists, would present some evidence that those theoretical differences are actually observable in the light fixture industry to the extent they cause chaos.

They didn't imagine it, because I and many others experienced it a lot.

Did he use one of 2015-referred CA-P427C / CA-P410C probes?

They forgot to quote you and the others.

Illuminant metameric error is tricky to deal with in the absence of the prospective illuminant spectrum. Your paint provider made a good, and presumably educated, guess.

Snapper-JACS, that' one creepy avatar ;-)

Brought to you by Bing AI or whatever they call it… That’s the future, l am afraid…

I know, I will change when I have the time.