colour.appearance.rlab Module¶

RLAB Colour Appearance Model¶

Defines RLAB colour appearance model objects:

• RLAB_VIEWING_CONDITIONS
• RLAB_D_FACTOR
• RLAB_Specification
• XYZ_to_RLAB()

References

colour.appearance.rlab.R_MATRIX = array([[ 1.9569, -1.1882, 0.2313], [ 0.3612, 0.6388, 0. ], [ 0. , 0. , 1. ]])¶

RLAB colour appearance model precomputed helper matrix.

R_MATRIX : array_like, (3, 3)

colour.appearance.rlab.RLAB_VIEWING_CONDITIONS = CaseInsensitiveMapping({u'Dark': 0.2857142857142857, u'Dim': 0.3448275862068966, u'Average': 0.4347826086956522})¶

Reference RLAB colour appearance model viewing conditions.

RLAB_VIEWING_CONDITIONS : CaseInsensitiveMapping

{‘Average’, ‘Dim’, ‘Dark’}

colour.appearance.rlab.RLAB_D_FACTOR = CaseInsensitiveMapping({u'Soft Copy Images': 0, u'Projected Transparencies, Dark Room': 0.5, u'soft_cp_img': 0, u'Hard Copy Images': 1, u'projected_dark': 0.5, u'hard_cp_img': 1})¶

RLAB colour appearance model Discounting-the-Illuminant factor values.

RLAB_D_FACTOR : CaseInsensitiveMapping

{‘Hard Copy Images’, ‘Soft Copy Images’, ‘Projected Transparencies, Dark Room’}

Aliases:

• ‘hard_cp_img’: ‘Hard Copy Images’
• ‘soft_cp_img’: ‘Soft Copy Images’
• ‘projected_dark’: ‘Projected Transparencies, Dark Room’

class colour.appearance.rlab.RLAB_ReferenceSpecification[source]¶

Bases: colour.appearance.rlab.RLAB_ReferenceSpecification

Defines the RLAB colour appearance model reference specification.

This specification has field names consistent with Fairchild (2013) reference.

Parameters:

LR (numeric or array_like) – Correlate of Lightness \(L^R\). CR (numeric or array_like) – Correlate of achromatic chroma \(C^R\). hR (numeric or array_like) – Hue angle \(h^R\) in degrees. sR (numeric or array_like) – Correlate of saturation \(s^R\). HR (numeric or array_like) – Hue \(h\) composition \(H^R\). aR (numeric or array_like) – Red–green chromatic response \(a^R\). bR (numeric or array_like) – Yellow–blue chromatic response \(b^R\).

class colour.appearance.rlab.RLAB_Specification[source]¶

Bases: colour.appearance.rlab.RLAB_Specification

Defines the RLAB colour appearance model specification.

This specification has field names consistent with the remaining colour appearance models in colour.appearance but diverge from Fairchild (2013) reference.

Parameters:

J (numeric or array_like) – Correlate of Lightness \(L^R\). C (numeric or array_like) – Correlate of achromatic chroma \(C^R\). h (numeric or array_like) – Hue angle \(h^R\) in degrees. s (numeric or array_like) – Correlate of saturation \(s^R\). HC (numeric or array_like) – Hue \(h\) composition \(H^C\). a (numeric or array_like) – Red–green chromatic response \(a^R\). b (numeric or array_like) – Yellow–blue chromatic response \(b^R\).

colour.appearance.rlab.XYZ_to_RLAB(XYZ, XYZ_n, Y_n, sigma=0.4347826086956522, D=1)[source]¶

Computes the RLAB model color appearance correlates.

Parameters:	XYZ (array_like) – CIE XYZ tristimulus values of test sample / stimulus in domain [0, 100]. XYZ_n (array_like) – CIE XYZ tristimulus values of reference white in domain [0, 100]. Y_n (numeric or array_like) – Absolute adapting luminance in \(cd/m^2\). sigma (numeric or array_like, optional) – Relative luminance of the surround, see RLAB_VIEWING_CONDITIONS for reference. D (numeric or array_like, optional) – Discounting-the-Illuminant factor in domain [0, 1].
Returns:	RLAB colour appearance model specification.
Return type:	RLAB_Specification

Warning

The input domain of that definition is non standard!

Notes

• Input CIE XYZ tristimulus values are in domain [0, 100].
• Input CIE XYZ_n tristimulus values are in domain [0, 100].

Examples

>>> XYZ = np.array([19.01, 20.00, 21.78])
>>> XYZ_n = np.array([109.85, 100, 35.58])
>>> Y_n = 31.83
>>> sigma = RLAB_VIEWING_CONDITIONS['Average']
>>> D = RLAB_D_FACTOR['Hard Copy Images']
>>> XYZ_to_RLAB(XYZ, XYZ_n, Y_n, sigma, D)  
RLAB_Specification(J=49.8347069..., C=54.8700585..., h=286.4860208..., s=1.1010410..., HC=None, a=15.5711021..., b=-52.6142956...)