colour.appearance.coefficient_q_Nayatani1997#

colour.appearance.coefficient_q_Nayatani1997(theta: ArrayLike) → NDArrayFloat[source]#

Return the \(q(\theta)\) coefficient for Nayatani (1997) HKE computations.

The hue angle \(\theta\) can be computed as follows:

\(tan^{-1}\cfrac{v' - v'_c}{u' - u'_c}\)

where \(u'\) and \(v'\) are the CIE 1976 chromaticity coordinates of the test chromatic light and \(u'_c\) and \(v'_c\) are the CIE 1976 chromaticity coordinates of the reference white light.

Parameters:: theta (ArrayLike) – Hue angle (\(\theta\)) in radians.
Returns:: \(q\) coefficient for Nayatani (1997) HKE methods.
Return type:: numpy.ndarray

References

[Nay97]

Examples

This recreates FIG. A-1.

>>> import matplotlib.pyplot as plt
>>> angles = [(np.pi * 2 / 100 * i) for i in range(100)]
>>> q_values = coefficient_q_Nayatani1997(angles)
>>> plt.plot(np.array(angles), q_values / (np.pi * 2) * 180)
... 
[<matplotlib.lines.Line2D object at 0x...>]
>>> plt.show()  