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 et al. (1958) method.
• lightness_wyszecki1964(): Lightness $W^*$ computation of given luminance $Y$ using Wyszecki (1964) method.
• lightness_1976(): Lightness $L^*$ computation of given luminance $Y$ as per CIE Lab implementation.

colour.colorimetry.lightness.lightness_glasser1958(Y, **kwargs)[source]¶

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

Parameters:	Y (numeric) – luminance $Y$. **kwargs (**, optional) – Unused parameter provided for signature compatibility with other Lightness computation objects.
Returns:	Lightness $L^*$.
Return type:	numeric

Notes

• Input luminance $Y$ is in domain [0, 100].
• Output Lightness $L^*$ is in domain [0, 100].

References

[1]	http://en.wikipedia.org/wiki/Lightness (Last accessed 13 April 2014)

Examples

>>> lightness_glasser1958(10.08)  
36.2505626...

colour.colorimetry.lightness.lightness_wyszecki1964(Y, **kwargs)[source]¶

Returns the Lightness $W^*$ of given luminance $Y$ using Wyszecki (1964) method.

Parameters:	Y (numeric) – luminance $Y$. **kwargs (**, optional) – Unused parameter provided for signature compatibility with other Lightness computation objects.
Returns:	Lightness $W^*$.
Return type:	numeric

Notes

• Input luminance $Y$ is in domain [0, 100].
• Output Lightness $W^*$ is in domain [0, 100].

References

[2]	http://en.wikipedia.org/wiki/Lightness (Last accessed 13 April 2014)

Examples

>>> lightness_wyszecki1964(10.08)  
37.0041149...

colour.colorimetry.lightness.lightness_1976(Y, Yn=100)[source]¶

Returns the Lightness $L^*$ of given luminance $Y$ using given reference white luminance $Y_n$ as per CIE Lab implementation.

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

Notes

• Input luminance $Y$ and $Y_n$ are in domain [0, 100].
• Output Lightness $L^*$ is in domain [0, 100].

References

[3]	http://www.poynton.com/PDFs/GammaFAQ.pdf (Last accessed 12 April 2014)

Examples

>>> lightness_1976(10.08)  
37.9856290...

colour.colorimetry.lightness.LIGHTNESS_METHODS = CaseInsensitiveMapping({u'Lstar1976': <function lightness_1976 at 0x102e0f488>, u'Wyszecki 1964': <function lightness_wyszecki1964 at 0x102e0f410>, u'CIE 1976': <function lightness_1976 at 0x102e0f488>, u'Glasser 1958': <function lightness_glasser1958 at 0x102e0f398>})¶

Supported Lightness computations methods.

LIGHTNESS_METHODS : dict

(‘Glasser 1958’, ‘Wyszecki 1964’, ‘CIE 1976’)

Aliases:

• ‘Lstar1976’: ‘CIE 1976’

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

Returns the Lightness $L^*$ using given method.

Parameters:	Y (numeric) – luminance $Y$. method (unicode, optional) – (‘Glasser 1958’, ‘Wyszecki 1964’, ‘CIE 1976’), Computation method. **kwargs (**) – Keywords arguments.
Returns:	Lightness $L^*$.
Return type:	numeric

Notes

• Input luminance $Y$ and optional $Y_n$ are in domain [0, 100].
• Output Lightness $L^*$ is in domain [0, 100].

Examples

>>> lightness(10.08)  
37.9856290...
>>> lightness(10.08, Yn=100)  
37.9856290...
>>> lightness(10.08, Yn=95)  
38.9165987...
>>> lightness(10.08, method='Glasser 1958')  
36.2505626...
>>> lightness(10.08, method='Wyszecki 1964')  
37.0041149...