# colour.models.derivation Module¶

## RGB Colourspace Derivation¶

Defines objects related to RGB colourspace derivation, essentially calculating the normalised primary matrix for given RGB colourspace primaries and whitepoint.

References

 [1] RP 177-1993 SMPTE RECOMMENDED PRACTICE - Television Color Equations, DOI: https://doi.org/10.5594/S9781614821915 (Last accessed 24 February 2014)
colour.models.derivation.xy_to_z(xy)[source]

Returns the z coordinate using given xy chromaticity coordinates.

Parameters: xy (array_like) – xy chromaticity coordinates. z coordinate. numeric

References

Examples

>>> xy_to_z((0.25, 0.25))
0.5

colour.models.derivation.normalised_primary_matrix(primaries, whitepoint)[source]

Returns the normalised primary matrix using given primaries and whitepoint matrices.

Parameters: primaries (array_like) – Primaries chromaticity coordinate matrix, (3, 2). whitepoint (array_like) – Illuminant / whitepoint chromaticity coordinates. Normalised primary matrix. ndarray, (3, 3)

References

Examples

>>> pms = np.array([0.73470, 0.26530, 0.00000, 1.00000, 0.00010, -0.07700])
>>> whitepoint = (0.32168, 0.33767)
>>> normalised_primary_matrix(pms, whitepoint)
array([[  9.5255239...e-01,   0.0000000...e+00,   9.3678631...e-05],
[  3.4396645...e-01,   7.2816609...e-01,  -7.2132546...e-02],
[  0.0000000...e+00,   0.0000000...e+00,   1.0088251...e+00]])

colour.models.derivation.RGB_luminance_equation(primaries, whitepoint)[source]

Returns the luminance equation from given primaries and whitepoint matrices.

Parameters: primaries (array_like, (3, 2)) – Primaries chromaticity coordinate matrix. whitepoint (array_like) – Illuminant / whitepoint chromaticity coordinates. Luminance equation. unicode

References

Examples

>>> pms = np.array([0.73470, 0.26530, 0.00000, 1.00000, 0.00010, -0.07700])
>>> whitepoint = (0.32168, 0.33767)
>>> # Doctests skip for Python 2.x compatibility.
>>> RGB_luminance_equation(pms, whitepoint)
'Y = 0.3439664...(R) + 0.7281660...(G) + -0.0721325...(B)'

colour.models.derivation.RGB_luminance(RGB, primaries, whitepoint)[source]

Returns the luminance $$y$$ of given RGB components from given primaries and whitepoint matrices.

Parameters: RGB (array_like, (3,)) – RGB chromaticity coordinate matrix. primaries (array_like, (3, 2)) – Primaries chromaticity coordinate matrix. whitepoint (array_like) – Illuminant / whitepoint chromaticity coordinates. Luminance $$y$$. numeric

References

Examples

>>> RGB = np.array([40.6, 4.2, 67.4])
>>> pms = np.array([0.73470, 0.26530, 0.00000, 1.00000, 0.00010, -0.07700])
>>> whitepoint = (0.32168, 0.33767)
>>> RGB_luminance(RGB, pms, whitepoint)
12.1616018...