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.

See also

RGB Colourspaces IPython Notebook

References

[1]	SMPTE. (1993). Derivation of Basic Television Color Equations. In RP 177:1993 (Vol. RP 177:199). doi:10.5594/S9781614821915

colour.models.derivation.xy_to_z(xy)[source]¶

Returns the z coordinate using given xy chromaticity coordinates.

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

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.
Returns:	Normalised primary matrix.
Return type:	ndarray, (3, 3)

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.
Returns:	Luminance equation.
Return type:	unicode

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.
Returns:	Luminance \(y\).
Return type:	numeric

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...