Add colour.XYZ_to_CIE1976UCS and colour.CIE1976UCS_to_XYZ definit…

…ions.

colour/__init__.py

@@ -298,6 +298,7 @@
     CAM16SCD_to_XYZ,
     CAM16UCS_to_JMh_CAM16,
     CAM16UCS_to_XYZ,
+    CIE1976UCS_to_XYZ,
     CMY_to_CMYK,
     CMY_to_RGB,
     CMYK_to_CMY,
@@ -362,6 +363,7 @@
     XYZ_to_CAM16LCD,
     XYZ_to_CAM16SCD,
     XYZ_to_CAM16UCS,
+    XYZ_to_CIE1976UCS,
     XYZ_to_DIN99,
     XYZ_to_hdr_CIELab,
     XYZ_to_hdr_IPT,
@@ -648,19 +650,20 @@
 ]
 __all__ += [
     "CAM02LCD_to_JMh_CIECAM02",
-    "CAM02SCD_to_JMh_CIECAM02",
-    "CAM02UCS_to_JMh_CIECAM02",
     "CAM02LCD_to_XYZ",
+    "CAM02SCD_to_JMh_CIECAM02",
     "CAM02SCD_to_XYZ",
+    "CAM02UCS_to_JMh_CIECAM02",
     "CAM02UCS_to_XYZ",
     "CAM16LCD_to_JMh_CAM16",
-    "CAM16SCD_to_JMh_CAM16",
-    "CAM16UCS_to_JMh_CAM16",
     "CAM16LCD_to_XYZ",
+    "CAM16SCD_to_JMh_CAM16",
     "CAM16SCD_to_XYZ",
+    "CAM16UCS_to_JMh_CAM16",
     "CAM16UCS_to_XYZ",
     "CCTF_DECODINGS",
     "CCTF_ENCODINGS",
+    "CIE1976UCS_to_XYZ",
     "CMYK_to_CMY",
     "CMY_to_CMYK",
     "CMY_to_RGB",
@@ -683,10 +686,10 @@
     "ICtCp_to_RGB",
     "ICtCp_to_XYZ",
     "IHLS_to_RGB",
-    "IgPgTg_to_XYZ",
+    "IPT_Ragoo2021_to_XYZ",
     "IPT_hue_angle",
     "IPT_to_XYZ",
-    "IPT_Ragoo2021_to_XYZ",
+    "IgPgTg_to_XYZ",
     "JMh_CAM16_to_CAM16LCD",
     "JMh_CAM16_to_CAM16SCD",
     "JMh_CAM16_to_CAM16UCS",
@@ -742,14 +745,15 @@
     "XYZ_to_CAM16LCD",
     "XYZ_to_CAM16SCD",
     "XYZ_to_CAM16UCS",
+    "XYZ_to_CIE1976UCS",
     "XYZ_to_DIN99",
     "XYZ_to_Hunter_Lab",
     "XYZ_to_Hunter_Rdab",
     "XYZ_to_ICaCb",
     "XYZ_to_ICtCp",
-    "XYZ_to_IgPgTg",
     "XYZ_to_IPT",
     "XYZ_to_IPT_Ragoo2021",
+    "XYZ_to_IgPgTg",
     "XYZ_to_Jzazbz",
     "XYZ_to_K_ab_HunterLab1966",
     "XYZ_to_Lab",
@@ -760,12 +764,12 @@
     "XYZ_to_RGB",
     "XYZ_to_UCS",
     "XYZ_to_UVW",
+    "XYZ_to_Yrg",
     "XYZ_to_hdr_CIELab",
     "XYZ_to_hdr_IPT",
     "XYZ_to_sRGB",
     "XYZ_to_xy",
     "XYZ_to_xyY",
-    "XYZ_to_Yrg",
     "YCbCr_to_RGB",
     "YCoCg_to_RGB",
     "YcCbcCrc_to_RGB",

colour/graph/conversion.py

@@ -77,6 +77,7 @@
     CAM16LCD_to_JMh_CAM16,
     CAM16SCD_to_JMh_CAM16,
     CAM16UCS_to_JMh_CAM16,
+    CIE1976UCS_to_XYZ,
     CMY_to_CMYK,
     CMY_to_RGB,
     CMYK_to_CMY,
@@ -129,6 +130,7 @@
     UCS_to_XYZ,
     UCS_uv_to_xy,
     UVW_to_XYZ,
+    XYZ_to_CIE1976UCS,
     XYZ_to_DIN99,
     XYZ_to_hdr_CIELab,
     XYZ_to_hdr_IPT,
@@ -672,6 +674,8 @@ def mired_to_CCT_D_uv(mired: ArrayLike) -> NDArrayFloat:
     ("CIE xy", "CIE Luv uv", xy_to_Luv_uv),
     ("CIE Luv", "CIE LCHuv", Luv_to_LCHuv),
     ("CIE LCHuv", "CIE Luv", LCHuv_to_Luv),
+    ("CIE 1976 UCS", "CIE XYZ", CIE1976UCS_to_XYZ),
+    ("CIE XYZ", "CIE 1976 UCS", XYZ_to_CIE1976UCS),
     ("CIE XYZ", "CIE UCS", XYZ_to_UCS),
     ("CIE UCS", "CIE XYZ", UCS_to_XYZ),
     ("CIE UCS", "CIE UCS uv", UCS_to_uv),

colour/models/__init__.py

@@ -60,6 +60,8 @@
     xy_to_Luv_uv,
     Luv_to_LCHuv,
     LCHuv_to_Luv,
+    XYZ_to_CIE1976UCS,
+    CIE1976UCS_to_XYZ,
 )
 from .cie_ucs import (
     XYZ_to_UCS,
@@ -429,6 +431,8 @@
     "xy_to_Luv_uv",
     "Luv_to_LCHuv",
     "LCHuv_to_Luv",
+    "XYZ_to_CIE1976UCS",
+    "CIE1976UCS_to_XYZ",
 ]
 __all__ += [
     "XYZ_to_UCS",

colour/models/cie_luv.py

@@ -12,6 +12,8 @@
 -   :func:`colour.xy_to_Luv_uv`
 -   :func:`colour.Luv_to_LCHuv`
 -   :func:`colour.LCHuv_to_Luv`
+-   :func:`colour.XYZ_to_CIE1976UCS`
+-   :func:`colour.CIE1976UCS_to_XYZ`
 
 References
 ----------
@@ -66,6 +68,8 @@
     "xy_to_Luv_uv",
     "Luv_to_LCHuv",
     "LCHuv_to_Luv",
+    "XYZ_to_CIE1976UCS",
+    "CIE1976UCS_to_XYZ",
 ]
 
 
@@ -534,3 +538,111 @@ def LCHuv_to_Luv(LCHuv: ArrayLike) -> NDArrayFloat:
     """
 
     return JCh_to_Jab(LCHuv)
+
+
+def XYZ_to_CIE1976UCS(
+    XYZ: ArrayLike,
+    illuminant: ArrayLike = CCS_ILLUMINANTS["CIE 1931 2 Degree Standard Observer"][
+        "D65"
+    ],
+) -> NDArrayFloat:
+    """
+    Convert from *CIE XYZ* tristimulus values to :math:`uv^pL\\*` colourspace.
+
+    This colourspace combines the :math:`uv^p` chromaticity coordinates with
+    the *Lightness* :math:`L\\*` from the *CIE L\\*u\\*v\\** colourspace.
+
+    It is a convenient definition to use with the
+    *CIE 1976 UCS Chromaticity Diagram*.
+
+    Parameters
+    ----------
+    XYZ
+        *CIE XYZ* tristimulus values.
+    illuminant
+        Reference *illuminant* *CIE xy* chromaticity coordinates or *CIE xyY*
+        colourspace array.
+
+    Returns
+    -------
+    :class:`numpy.ndarray`
+        :math:`uv^pL\\*` colourspace array.
+
+    Notes
+    -----
+    +----------------+-----------------------+-----------------+
+    | **Domain**     | **Scale - Reference** | **Scale - 1**   |
+    +================+=======================+=================+
+    | ``XYZ``        | [0, 1]                | [0, 1]          |
+    +----------------+-----------------------+-----------------+
+    | ``illuminant`` | [0, 1]                | [0, 1]          |
+    +----------------+-----------------------+-----------------+
+
+    Examples
+    --------
+    >>> import numpy as np
+    >>> XYZ = np.array([0.20654008, 0.12197225, 0.05136952])
+    >>> XYZ_to_CIE1976UCS(XYZ)  # doctest: +ELLIPSIS
+    array([  0.3772021...,   0.5012026...,  41.5278752...])
+    """
+
+    Luv = XYZ_to_Luv(XYZ, illuminant)
+
+    L, _u, _v = tsplit(Luv)
+
+    u, v = tsplit(Luv_to_uv(Luv, illuminant))
+
+    return tstack([u, v, L])
+
+
+def CIE1976UCS_to_XYZ(
+    uvL: ArrayLike,
+    illuminant: ArrayLike = CCS_ILLUMINANTS["CIE 1931 2 Degree Standard Observer"][
+        "D65"
+    ],
+) -> NDArrayFloat:
+    """
+    Convert from *CIE XYZ* tristimulus values to :math:`uv^pL\\*` colourspace.
+
+    This colourspace combines the :math:`uv^p` chromaticity coordinates with
+    the *Lightness* :math:`L\\*` from the *CIE L\\*u\\*v\\** colourspace.
+
+    It is a convenient definition to use with the
+    *CIE 1976 UCS Chromaticity Diagram*.
+
+    Parameters
+    ----------
+    uvL
+        :math:`uv^pL\\*` colourspace array.
+    illuminant
+        Reference *illuminant* *CIE xy* chromaticity coordinates or *CIE xyY*
+        colourspace array.
+
+    Returns
+    -------
+    :class:`numpy.ndarray`
+        :math:`uv^pL\\*` colourspace array.
+
+    Notes
+    -----
+    +----------------+-----------------------+-----------------+
+    | **Domain**     | **Scale - Reference** | **Scale - 1**   |
+    +================+=======================+=================+
+    | ``XYZ``        | [0, 1]                | [0, 1]          |
+    +----------------+-----------------------+-----------------+
+    | ``illuminant`` | [0, 1]                | [0, 1]          |
+    +----------------+-----------------------+-----------------+
+
+    Examples
+    --------
+    >>> import numpy as np
+    >>> uvL = np.array([0.37720213, 0.50120264, 41.52787529])
+    >>> CIE1976UCS_to_XYZ(uvL)  # doctest: +ELLIPSIS
+    array([ 0.2065400...,  0.1219722...,  0.0513695...])
+    """
+
+    u, v, L = tsplit(uvL)
+
+    _L, u, v = tsplit(uv_to_Luv(tstack([u, v]), illuminant, L))
+
+    return Luv_to_XYZ(tstack([L, u, v]), illuminant)

colour/models/common.py

@@ -63,6 +63,7 @@
     "CAM16LCD",
     "CAM16SCD",
     "CAM16UCS",
+    "CIE 1976 UCS",
     "CIE Lab",
     "CIE Luv",
     "CIE UCS",
@@ -106,6 +107,7 @@
         "CAM16LCD": ("$J^'$", "$a^'$", "$b^'$"),
         "CAM16SCD": ("$J^'$", "$a^'$", "$b^'$"),
         "CAM16UCS": ("$J^'$", "$a^'$", "$b^'$"),
+        "CIE 1976 UCS": ("$u^'$", "$v^'$", "$L^*$"),
         "CIE Lab": ("$L^*$", "$a^*$", "$b^*$"),
         "CIE Luv": ("$L^*$", "$u^'$", "$v^'$"),
         "CIE UCS": ("U", "V", "W"),
@@ -148,6 +150,7 @@
             "CAM16LCD": np.array([100, 100, 100]),
             "CAM16SCD": np.array([100, 100, 100]),
             "CAM16UCS": np.array([100, 100, 100]),
+            "CIE 1976 UCS": np.array([1, 1, 100]),
             "CIE Lab": np.array([100, 100, 100]),
             "CIE Luv": np.array([100, 100, 100]),
             "CIE UCS": np.array([1, 1, 1]),