# colour.appearance.coefficient_q_Nayatani1997¶

colour.appearance.coefficient_q_Nayatani1997(theta: FloatingOrArrayLike) FloatingOrNDArray[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 (FloatingOrArrayLike) – Hue angle ($$\theta$$) in radians.

Returns

$$q$$ coefficient for Nayatani (1997) HKE methods.

Return type

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()