This question arose in an email discussion in which there was some question as to the actual “sRGB blue” LCh and JCh values.

Here are ArgyllCMS xicclu (xicclu) adapted and unadapted LCh values for the sRGB blue primary (that is, (0,0,255), (0.0, 0.0, 1.0), etc, depending on the bit depth)):

relative (adapted to D50): $ xicclu -ir -pL sRGB.icm

L=29.57

C=131.21

h=301.36

absolute (unadapted): $ xicclu -ia -pL sRGB.icm

L=32.30

C=148.44

h=301.62

The above adapted values are also what you get in GIMP, PhotoFlow, RawTherapee, though in RawTherapee you get LAB values, but the LAB values agree with GIMP LAB values.

Apparently https://www.colour-science.org/ calculations come up with a different set of LCh values for sRGB blue, compared to ArgyllCMS values. The discrepancies are worse for JCh values. The other party to the email discussion should be coming along soon to post the colour-science values, I hope .

In the meantime, these three websites: http://davidjohnstone.net/pages/lch-lab-colour-gradient-picker , Convert Rgb to Lch , Convert | EasyRGB all come up with values of approximately:

L=32.30

C=133.82

h=306.29

So the above three websites come up with values that are in agreement with each other but only “somewhat close” to ArgyllCMS “xicclu” unadapted LCh values.

I suspect all three websites might have gotten their D65 and D50 white points from brucelindbloom.com (Welcome to Bruce Lindbloom's Web Site), which uses ASTM values instead of the D65 values from the sRGB specs and the D50 values from the ICC specs, which might account for the discrepancies for the LCh values.

For JCh, there are a bunch of other parameters to consider beside the white point values, and I don’t know what default values ArgyllCMS xicclu actually uses for these other parameters. But for comparison (again, assuming the other party to the email discussion does post colour-science values ) here are the ArgyllCMS xicclu values:

adapted: $ xicclu -ir -pJ sRGB.icm

L=29.15

C=92.77

h=273.15

unadapted: $ xicclu -ia -pJ sRGB.icm

L=32.12

C=100.70

h=272.72

edit: in the lines immediately above, “L” of course should be “J”, sorry! I should have just copy-pasted the xicclu output instead of trying to make the lines look pretty. Sigh.