[suzumer]

Cam16 (as opposed to cam16 ucs) is perception based. It calculates chroma, lightness, and hue, and is based on the munsell color system. Hellwig and Fairchild recently simplifed the model mathematically, improving it's chroma accuracy.( http://markfairchild.org/PDFs/PAP45.pdf) Another, simpler, model is CIELAB, which outputs paramters L, a, and b, where L is lightness, hypot(a,b) is chroma, and arctan2(b,a) is the hue.

[mncharity]

Thanks! IIRC(fuzzily - it's been a while), I chose -UCS for a more euclidean color difference metric - I should review that. My even fuzzier recollection, is CIELAB's visible gamut shape is very artifacty[1], perhaps misleadingly representing the volume outside sRGB/P3 for instance.

The pedagogical objectives of playing well with full visible 3D gamut, and spectral locus, and of avoiding shape artifacts (concavities, excursions), are... non-traditional. Characteristics which could be happily traded away in traditional uses of color spaces, for characteristics like model math and simplicity which here have near-zero value (lookup tables satisficing). And were - most spaces have "oh my, that's a hard downselect" bizarre visual hulls, and topologies outside of P3 or even sRGB can get quite strange. Thus the need to untwist CAM16's curving hue lines - they're not bad within sRGB, but by the time they hit visible hull, yipes, I recall some as near parallel to hull.

Having a color space to play with as a realistic 3D whole, seems not the kind of thing we collectively incentivize. A lot of science education content difficulty seems like that.

[1] https://commons.wikimedia.org/wiki/File:Visible_gamut_within...

[suzumer]

CAM16's hue lines are curved by design. Hue is not linear with regards to xy chromaticity, as evidenced by the Abney effect[1].

[1] https://en.wikipedia.org/wiki/Abney_effect