colour.appearance.rlab Module

RLAB Colour Appearance Model

Defines RLAB colour appearance model objects:

See also

RLAB Colour Appearance Model IPython Notebook

References

[1]Mark D. Fairchild, Refinement of the RLAB color space, Color Research & Application, Volume 21, Issue 5, pages 338–346, October 1996, https://ritdml.rit.edu/bitstream/handle/1850/7857/MFairchildArticle12-06-1998.pdf (Last accessed 16 August 2014)
[2]Mark D. Fairchild, Color Appearance Models, 3nd Edition, The Wiley-IS&T Series in Imaging Science and Technology, published June 2013, ASIN: B00DAYO8E2, locations 6019-6178.
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 : dict
(‘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 : dict
(‘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 Mark D. Fairchild reference.

Parameters:
  • LR (numeric) – Correlate of Lightness \(L^R\).
  • CR (numeric) – Correlate of achromatic chroma \(C^R\).
  • hR (numeric) – Hue angle \(h^R\) in degrees.
  • sR (numeric) – Correlate of saturation \(s^R\).
  • HR (numeric) – Hue \(h\) composition \(H^R\).
  • aR (numeric) – Red–green chromatic response \(a^R\).
  • bR (numeric) – 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 Mark D. Fairchild reference.

Parameters:
  • J (numeric) – Correlate of Lightness \(L^R\).
  • C (numeric) – Correlate of achromatic chroma \(C^R\).
  • h (numeric) – Hue angle \(h^R\) in degrees.
  • s (numeric) – Correlate of saturation \(s^R\).
  • HC (numeric) – Hue \(h\) composition \(H^C\).
  • a (numeric) – Red–green chromatic response \(a^R\).
  • b (numeric) – 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, (3, n)) – CIE XYZ colourspace matrix of test sample / stimulus in domain [0, 100].
  • XYZ_n (array_like, (3,)) – CIE XYZ colourspace matrix of reference white in domain [0, 100].
  • Y_n (numeric) – Absolute adapting luminance in \(cd/m^2\).
  • sigma (numeric, optional) – Relative luminance of the surround, see RLAB_VIEWING_CONDITIONS for reference.
  • D (numeric, 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 colourspace matrix is in domain [0, 100].
  • Input CIE XYZ_n colourspace matrix is in domain [0, 100].

Examples

>>> XYZ = np.array([19.01, 20, 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...)