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]	RP 177-1993 SMPTE RECOMMENDED PRACTICE - Television Color Equations (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.
Returns:	z coordinate.
Return type:	numeric

References

[2]	RP 177-1993 SMPTE RECOMMENDED PRACTICE - Television Color Equations: 3.3.2

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)

References

[3]	RP 177-1993 SMPTE RECOMMENDED PRACTICE - Television Color Equations: 3.3.2 - 3.3.6

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

References

[4]	RP 177-1993 SMPTE RECOMMENDED PRACTICE - Television Color Equations: 3.3.8

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

References

[5]	RP 177-1993 SMPTE RECOMMENDED PRACTICE - Television Color Equations: 3.3.3 - 3.3.6

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...