colour.colorimetry.tristimulus Module¶

Tristimulus Values¶

Defines objects for tristimulus values computation from spectral data.

colour.colorimetry.tristimulus.spectral_to_XYZ(spd, cmfs=<colour.colorimetry.cmfs.XYZ_ColourMatchingFunctions object at 0x102e0ccd0>, illuminant=None)[source]¶

Converts given spectral power distribution to CIE XYZ colourspace using given colour matching functions and illuminant.

Parameters:	spd (SpectralPowerDistribution) – Spectral power distribution. cmfs (XYZ_ColourMatchingFunctions) – Standard observer colour matching functions. illuminant (SpectralPowerDistribution, optional) – Illuminant spectral power distribution.
Returns:	CIE XYZ colourspace matrix.
Return type:	ndarray, (3,)

Warning

The output domain of that definition is non standard!

Notes

Output CIE XYZ colourspace matrix is in domain [0, 100].

References

[1]	Wyszecki & Stiles, Color Science - Concepts and Methods Data and Formulae - Second Edition, Wiley Classics Library Edition, published 2000, ISBN-10: 0-471-39918-3, page 158.

Examples

>>> from colour import CMFS, ILLUMINANTS_RELATIVE_SPDS, SpectralPowerDistribution  
>>> cmfs = CMFS.get('CIE 1931 2 Degree Standard Observer')
>>> data = {380: 0.0600, 390: 0.0600}
>>> spd = SpectralPowerDistribution('Custom', data)
>>> illuminant = ILLUMINANTS_RELATIVE_SPDS.get('D50')
>>> spectral_to_XYZ(spd, cmfs, illuminant)  
array([  4.5764852...e-04,   1.2964866...e-05,   2.1615807...e-03])

colour.colorimetry.tristimulus.wavelength_to_XYZ(*args, **kwds)[source]¶

Converts given wavelength $\lambda$ to CIE XYZ colourspace using given colour matching functions.

If the wavelength $\lambda$ is not available in the colour matching function, its value will be calculated using CIE recommendations: The method developed by Sprague (1880) should be used for interpolating functions having a uniformly spaced independent variable and a Cubic Spline method for non-uniformly spaced independent variable.

Parameters:	wavelength (numeric) – Wavelength $\lambda$ in nm. cmfs (XYZ_ColourMatchingFunctions, optional) – Standard observer colour matching functions.
Returns:	CIE XYZ colourspace matrix.
Return type:	ndarray, (3,)
Raises:	`ValueError` – If wavelength $\lambda$ is not in the colour matching functions domain.

Notes

Output CIE XYZ colourspace matrix is in domain [0, 1].
If scipy is not unavailable the Cubic Spline method will fallback to legacy Linear interpolation.

Examples

>>> from colour import CMFS
>>> cmfs = CMFS.get('CIE 1931 2 Degree Standard Observer')
>>> wavelength_to_XYZ(480)  
array([ 0.09564  ,  0.13902  ,  0.812950...])