@KelSolaar and @gwgill - thanks! for the references and for letting me know that CIECAM02 really is more perceptually uniform than LAB.
Regarding the problem of having been fitted to a data set that wasn’t large enough, even in the digital darkroom my own interest is strictly in colors that can be printed or painted (using the same pigments artists use) without resorting to optical brighteners or other exotic ways to make colors brighter or more saturated. So a practical question is this: When working in a large RGB color space like Rec.2020 (sRGB excludes far too many paintable and printable colors), and keeping as far away from the primaries as required to avoid unprintable/not-paintable colors, how badly would the “fitted to a too-small dataset” affect using JCh? In case this question is just plain confused, please enlighten!
A couple of years ago I got a copy of Fairchild’s Color Appearance Models from our local library and read it. At the time my reaction was “That book needs actual pictures to illustrate the disadvantages of each model, that in turn led to the creation of the next model”. But I’ll check it out again and try rereading it, and also see if I can find a copy of the Luo paper - fortunately we have a university library nearby that allows non-students to use their resources.
Regarding the possibility (that would surely make @afre happy I’m guessing!) of perhaps adding code to GIMP that would allow picking colors using JCh (some version of), just how complicated are the equations, assuming one sets the “appearance model” parts to be as simple as possible? I’ve been looking for something for JCh that’s along the lines of Lindbloom’s explanation of the XYZ to LAB equations, such that I could focus more on “turn the equations into code” and less on “by the way what do these equations actually mean” - is there such a reference? I’ve looked at the ArgyllCMS code, but haven’t really been able to figure out where to start in terms of “What does this code actually do to modify the input XYZ values”, such that maybe I could write similar code for GIMP.
I think that would be nice to find a balance between making images and improving image-making software. Maybe schedule in a painting between rounds of coding?
Regarding subtractive rather than additive, I got the impression that the Wikipedia article was only talking about adding white light to monochromatic light, and not about mixing actual paint pigments on a surface and looking at the resulting color, so only applies to additively mixed colors. Anyway, I pulled out my oil pastels and mixed blue with white to make a fairly long more or less even gradient, and the apparent hue didn’t change much if at all, stayed blue all the way. But maybe the blue wasn’t violet enough.
On the other hand, mixing bright yellow oil pastel with black (or rather a mixture of black and white) does make olive green precisley as discussed on MacEvoy’s website. So is the Abney effect only about adding white light to monochromatic light? Or is it also about adding black pigment to make darker colors from bright pigments?
I had never heard of the Abney effect so thanks! for the link.
Anyway, @briend - you’ve convinced me of the value of your spectral subtractive mixing - anything that avoids that awful transition from blue to purple when mixing in white has got to be a step in the right direction .
Would you be willing to show some samples mixing magenta with cyan? I spent some time mixing oil pastels, using the nearest Crayola Portfolio yellow, cyan, and magenta working from MacEvoy’s page on triad color palettes handprint : "primary" triad palette, and was surprised by how much darker the purples, blues, and green-blues that you get from mixing the cyan and magenta oil pastels are, compared to the unmixed colors. Yes, I know, subtractive color mixing and all, of course the mixed color is darker. But “knowing” and “seeing” are two different things. So I’m curious as to how your spectral mixing algorithms handle colors like cyan and magenta (I think I already sent you approximate LCh values for the Portfolio pastels).