Thanks for correcting. About color science, something I don't know keeps coming up.

Is that why CAM16 JMh exists?

Anyway, Jab_to_JCh is just used to convert cartesian to cylindrical. Not to get actual J, C, h value. Relative position on the CAM16-UCS's a-b plane is what I want to get. So, I think it's fine for the purpose.

(I don't want to use CIELAB because its hue prediction is bad, especially reddish blue.)