colour.colorimetry.lightness Module¶

Lightness \(L\)¶

Defines Lightness \(L\) computation objects.

The following methods are available:

lightness_Glasser1958(): Lightness \(L\) computation of given luminance \(Y\) using Glasser, Mckinney, Reilly and Schnelle (1958) method.
lightness_Wyszecki1963(): Lightness \(W\) computation of given luminance \(Y\) using Wyszecki (1963)⁠⁠⁠⁠ method.
lightness_CIE1976(): Lightness \(L^*\) computation of given luminance \(Y\) as per CIE 1976 recommendation.
lightness_Fairchild2010(): Lightness \(L_{hdr}\) computation of given luminance \(Y\) using Fairchild and Wyble (2010) method.

See also

References

[1]	Wikipedia. (n.d.). Lightness. Retrieved April 13, 2014, from http://en.wikipedia.org/wiki/Lightness

colour.colorimetry.lightness.lightness_Glasser1958(Y)[source]¶

Returns the Lightness \(L\) of given luminance \(Y\) using Glasser et al. (1958) method.

Parameters:	Y (numeric or array_like) – luminance \(Y\).
Returns:	Lightness \(L\).
Return type:	numeric or array_like

Notes

Input luminance \(Y\) is in domain [0, 100].
Output Lightness \(L\) is in range [0, 100].

References

[2]	Glasser, L. G., McKinney, A. H., Reilly, C. D., & Schnelle, P. D. (1958). Cube-Root Color Coordinate System. J. Opt. Soc. Am., 48(10), 736–740. doi:10.1364/JOSA.48.000736

Examples

>>> lightness_Glasser1958(10.08)  
36.2505626...

colour.colorimetry.lightness.lightness_Wyszecki1963(Y)[source]¶

Returns the Lightness \(W\) of given luminance \(Y\) using Wyszecki (1963) method.

Parameters:	Y (numeric or array_like) – luminance \(Y\).
Returns:	Lightness \(W\).
Return type:	numeric or array_like

Notes

Input luminance \(Y\) is in domain [0, 100].
Output Lightness \(W\) is in range [0, 100].

References

[3]	Wyszecki, G. (1963). Proposal for a New Color-Difference Formula. J. Opt. Soc. Am., 53(11), 1318–1319. doi:10.1364/JOSA.53.001318

Examples

>>> lightness_Wyszecki1963(10.08)  
37.0041149...

colour.colorimetry.lightness.lightness_CIE1976(Y, Y_n=100)[source]¶

Returns the Lightness \(L^*\) of given luminance \(Y\) using given reference white luminance \(Y_n\) as per CIE 1976 recommendation.

Parameters:	Y (numeric or array_like) – luminance \(Y\). Y_n (numeric or array_like, optional) – White reference luminance \(Y_n\).
Returns:	Lightness \(L^*\).
Return type:	numeric or array_like

Notes

Input luminance \(Y\) and \(Y_n\) are in domain [0, 100].
Output Lightness \(L^*\) is in range [0, 100].

References

[4]	Wyszecki, G., & Stiles, W. S. (2000). CIE 1976 (Luv*)-Space and Color-Difference Formula. In Color Science: Concepts and Methods, Quantitative Data and Formulae (p. 167). Wiley. ISBN:978-0471399186

[5]	Lindbloom, B. (2003). A Continuity Study of the CIE L* Function. Retrieved February 24, 2014, from http://brucelindbloom.com/LContinuity.html

Examples

>>> lightness_CIE1976(10.08)  
array(37.9856290...)

colour.colorimetry.lightness.lightness_Fairchild2010(Y, epsilon=2)[source]¶

Computes Lightness \(L_{hdr}\) of given luminance \(Y\) using Fairchild and Wyble (2010) method accordingly to Michealis-Menten kinetics.

Parameters:	Y (array_like) – luminance \(Y\). epsilon (numeric or array_like, optional) – \(\epsilon\) exponent.
Returns:	Lightness \(L_{hdr}\).
Return type:	array_like

Warning

The input domain of that definition is non standard!

Notes

Input luminance \(Y\) is in domain [0, \(\infty\)].

References

[6]	Fairchild, M. D., & Wyble, D. R. (2010). hdr-CIELAB and hdr-IPT: Simple Models for Describing the Color of High-Dynamic-Range and Wide-Color-Gamut Images. In Proc. of Color and Imaging Conference (pp. 322–326). ISBN:9781629932156

Examples

>>> lightness_Fairchild2010(10.08 / 100, 1.836)  
24.9022902...

colour.colorimetry.lightness.LIGHTNESS_METHODS = CaseInsensitiveMapping({u'Lstar1976': <function lightness_CIE1976>, u'Wyszecki 1963': <function lightness_Wyszecki1963>, u'Fairchild 2010': <function lightness_Fairchild2010>, u'CIE 1976': <function lightness_CIE1976>, u'Glasser 1958': <function lightness_Glasser1958>})¶

Supported Lightness computations methods.

LIGHTNESS_METHODS : CaseInsensitiveMapping: {‘Glasser 1958’, ‘Wyszecki 1963’, ‘CIE 1976’, ‘Fairchild 2010’}

Aliases:

‘Lstar1976’: ‘CIE 1976’

colour.colorimetry.lightness.lightness(Y, method=u'CIE 1976', **kwargs)[source]¶

Returns the Lightness \(L\) using given method.

Other Parameters:
Parameters:	Y (numeric or array_like) – luminance \(Y\). method (unicode, optional) – {‘CIE 1976’, ‘Glasser 1958’, ‘Wyszecki 1963’, ‘Fairchild 2010’}, Computation method.
	Y_n (numeric or array_like, optional) – {`lightness_CIE1976()`}, White reference luminance \(Y_n\). epsilon (numeric or array_like, optional) – {`lightness_Fairchild2010()`}, \(\epsilon\) exponent.
Returns:	Lightness \(L\).
Return type:	numeric or array_like

Notes

Input luminance \(Y\) and optional \(Y_n\) are in domain [0, 100] or [0, \(\infty\)].
Output Lightness \(L\) is in range [0, 100].

Examples

>>> lightness(10.08)  
array(37.9856290...)
>>> lightness(10.08, Y_n=100)  
array(37.9856290...)
>>> lightness(10.08, Y_n=95)  
array(38.9165987...)
>>> lightness(10.08, method='Glasser 1958')  
36.2505626...
>>> lightness(10.08, method='Wyszecki 1963')  
37.0041149...
>>> lightness(
...     10.08 / 100,
...     epsilon=1.836,
...     method='Fairchild 2010')  
24.9022902...