add HyCH color difference metric

add HyCH tests

colour/difference/__init__.py

@@ -54,6 +54,7 @@
     delta_E_CMC,
     delta_E_ITP,
     delta_E_HyAB,
+    delta_E_HyCH,
 )
 from .din99 import delta_E_DIN99
 from .huang2015 import power_function_Huang2015
@@ -77,6 +78,7 @@
     "delta_E_CMC",
     "delta_E_ITP",
     "delta_E_HyAB",
+    "delta_E_HyCH",
 ]
 __all__ += [
     "delta_E_DIN99",
@@ -105,6 +107,7 @@
         "CAM16-UCS": delta_E_CAM16UCS,
         "DIN99": delta_E_DIN99,
         "HyAB": delta_E_HyAB,
+        "HyCH": delta_E_HyCH,
     }
 )
 DELTA_E_METHODS.__doc__ = """
@@ -210,6 +213,10 @@ def delta_E(
     >>> b = np.array([53.12207516, -39.92365056, 249.54831278])
     >>> delta_E(a, b, method="HyAB")  # doctest: +ELLIPSIS
     151.0215481...
+    >>> a = np.array([39.91531343, 51.16658481, 146.12933781])
+    >>> b = np.array([53.12207516, -39.92365056, 249.54831278])
+    >>> delta_E(a, b, method="HyCH")  # doctest: +ELLIPSIS
+    48.66427941...
     """
 
     method = validate_method(method, tuple(DELTA_E_METHODS))

colour/difference/delta_e.py

@@ -13,6 +13,7 @@
 -   :func:`colour.difference.delta_E_CMC`
 -   :func:`colour.difference.delta_E_ITP`
 -   :func:`colour.difference.delta_E_HyAB`
+-   :func:`colour.difference.delta_E_HyCH`
 
 References
 ----------
@@ -79,6 +80,7 @@
     "delta_E_CMC",
     "delta_E_ITP",
     "delta_E_HyAB",
+    "delta_E_HyCH",
 ]
 
 JND_CIE1976 = 2.3
@@ -712,3 +714,68 @@ def delta_E_HyAB(Lab_1: ArrayLike, Lab_2: ArrayLike) -> NDArrayFloat:
     HyAB = np.abs(dL) + np.hypot(da, db)
 
     return as_float(HyAB)
+
+
+def delta_E_HyCH(
+    Lab_1: ArrayLike, Lab_2: ArrayLike, textiles: bool = False
+) -> NDArrayFloat:
+    """
+    Return the difference between two *CIE L\\*a\\*b\\** colourspace arrays
+    This metric is intended for large color differences,
+    on the order of 10 CIELAB units or greater
+
+    Parameters
+    ----------
+    Lab_1
+        *CIE L\\*a\\*b\\** colourspace array 1.
+    Lab_2
+        *CIE L\\*a\\*b\\** colourspace array 2.
+
+    Returns
+    -------
+    :class:`numpy.ndarray`
+        Colour difference HyCH.
+
+    Notes
+    -----
+    +------------+-----------------------+-------------------+
+    | **Domain** | **Scale - Reference** | **Scale - 1**     |
+    +============+=======================+===================+
+    | ``Lab_1``  | ``L_1`` : [0, 100]    | ``L_1`` : [0, 1]  |
+    |            |                       |                   |
+    |            | ``a_1`` : [-100, 100] | ``a_1`` : [-1, 1] |
+    |            |                       |                   |
+    |            | ``b_1`` : [-100, 100] | ``b_1`` : [-1, 1] |
+    +------------+-----------------------+-------------------+
+    | ``Lab_2``  | ``L_2`` : [0, 100]    | ``L_2`` : [0, 1]  |
+    |            |                       |                   |
+    |            | ``a_2`` : [-100, 100] | ``a_2`` : [-1, 1] |
+    |            |                       |                   |
+    |            | ``b_2`` : [-100, 100] | ``b_2`` : [-1, 1] |
+    +------------+-----------------------+-------------------+
+
+    References
+    ----------
+    :cite:`Abasi2020`
+
+    Examples
+    --------
+    >>> Lab_1 = np.array([39.91531343, 51.16658481, 146.12933781])
+    >>> Lab_2 = np.array([53.12207516, -39.92365056, 249.54831278])
+    >>> delta_E_HyCH(Lab_1, Lab_2)  # doctest: +ELLIPSIS
+    48.664279419760369...
+    """
+
+    S_L, S_C, S_H, delta_L_p, delta_C_p, delta_H_p, R_T = astuple(
+        intermediate_attributes_CIE2000(Lab_1, Lab_2)
+    )
+
+    k_L = 2 if textiles else 1
+    k_C = 1
+    k_H = 1
+
+    HyCH = np.abs(delta_L_p / (k_L * S_L)) + np.sqrt(
+        (delta_C_p / (k_C * S_C)) ** 2 + (delta_H_p / (k_H * S_H)) ** 2
+    )
+
+    return as_float(HyCH)

colour/difference/tests/test_delta_e.py

@@ -21,6 +21,7 @@
     delta_E_CIE2000,
     delta_E_CMC,
     delta_E_HyAB,
+    delta_E_HyCH,
     delta_E_ITP,
 )
 from colour.difference.delta_e import intermediate_attributes_CIE2000
@@ -40,6 +41,7 @@
     "TestDelta_E_CMC",
     "TestDelta_E_ITP",
     "TestDelta_E_HyAB",
+    "TestDelta_E_HyCH",
 ]
 
 
@@ -918,3 +920,98 @@ def test_nan_delta_E_HyAB(self):
         cases = [-1.0, 0.0, 1.0, -np.inf, np.inf, np.nan]
         cases = np.array(list(set(product(cases, repeat=3))))
         delta_E_HyAB(cases, cases)
+
+
+class TestDelta_E_HyCH:
+    """
+    Define :func:`colour.difference.delta_e.delta_E_HyCH` definition unit
+    tests methods.
+    """
+
+    def test_delta_E_HyCH(self):
+        """Test :func:`colour.difference.delta_e.delta_E_HyCH` definition."""
+
+        np.testing.assert_allclose(
+            delta_E_HyCH(
+                np.array([39.91531343, 51.16658481, 146.12933781]),
+                np.array([53.12207516, -39.92365056, 249.54831278]),
+            ),
+            48.664279419760369,
+            atol=TOLERANCE_ABSOLUTE_TESTS,
+        )
+
+        np.testing.assert_allclose(
+            delta_E_HyCH(
+                np.array([39.91531343, 51.16658481, 146.12933781]),
+                np.array([28.52234779, 19.46628874, 472.06042624]),
+            ),
+            39.260928157999118,
+            atol=TOLERANCE_ABSOLUTE_TESTS,
+        )
+
+        np.testing.assert_allclose(
+            delta_E_HyCH(
+                np.array([48.99183622, -0.10561667, 400.65619925]),
+                np.array([50.65907324, -0.11671910, 402.82235718]),
+            ),
+            1.7806293290163562,
+            atol=TOLERANCE_ABSOLUTE_TESTS,
+        )
+
+    def test_n_dimensional_delta_E_HyCH(self):
+        """
+        Test :func:`colour.difference.delta_e.delta_E_HyCH` definition
+        n-dimensional arrays support.
+        """
+
+        Lab_1 = (np.array([39.91531343, 51.16658481, 146.12933781]),)
+        Lab_2 = (np.array([53.12207516, -39.92365056, 249.54831278]),)
+        delta_E = delta_E_HyCH(Lab_1, Lab_2)
+
+        Lab_1 = np.tile(Lab_1, (6, 1))
+        Lab_2 = np.tile(Lab_2, (6, 1))
+        delta_E = np.tile(delta_E, 6)
+        np.testing.assert_allclose(
+            delta_E_HyCH(Lab_1, Lab_2),
+            delta_E,
+            atol=TOLERANCE_ABSOLUTE_TESTS,
+        )
+
+        Lab_1 = np.reshape(Lab_1, (2, 3, 3))
+        Lab_2 = np.reshape(Lab_2, (2, 3, 3))
+        delta_E = np.reshape(delta_E, (2, 3))
+        np.testing.assert_allclose(
+            delta_E_HyCH(Lab_1, Lab_2),
+            delta_E,
+            atol=TOLERANCE_ABSOLUTE_TESTS,
+        )
+
+    def test_domain_range_scale_delta_E_HyCH(self):
+        """
+        Test :func:`colour.difference.delta_e.delta_E_HyCH` definition
+        domain and range scale support.
+        """
+
+        Lab_1 = np.array([39.91531343, 51.16658481, 146.12933781])
+        Lab_2 = np.array([53.12207516, -39.92365056, 249.54831278])
+        delta_E = delta_E_HyCH(Lab_1, Lab_2)
+
+        d_r = (("reference", 1), ("1", 0.01), ("100", 1))
+        for scale, factor in d_r:
+            with domain_range_scale(scale):
+                np.testing.assert_allclose(
+                    delta_E_HyCH(Lab_1 * factor, Lab_2 * factor),
+                    delta_E,
+                    atol=TOLERANCE_ABSOLUTE_TESTS,
+                )
+
+    @ignore_numpy_errors
+    def test_nan_delta_E_HyCH(self):
+        """
+        Test :func:`colour.difference.delta_e.delta_E_HyCH` definition nan
+        support.
+        """
+
+        cases = [-1.0, 0.0, 1.0, -np.inf, np.inf, np.nan]
+        cases = np.array(list(set(product(cases, repeat=3))))
+        delta_E_HyCH(cases, cases)

colour/hints/__init__.py

@@ -589,6 +589,7 @@ def apply(self, RGB: ArrayLike, **kwargs: Any) -> NDArray:  # noqa: D102
     "CMC",
     "DIN99",
     "HyAB",
+    "HyCH",
     "ITP",
     "cie1976",
     "cie1994",

docs/colour.difference.rst

@@ -127,6 +127,18 @@ HyAB
 
     delta_E_HyAB
 
+HyCH
+-----
+
+``colour.difference``
+
+.. currentmodule:: colour.difference
+
+.. autosummary::
+    :toctree: generated/
+
+    delta_E_HyCH
+
 Standardized Residual Sum of Squares (STRESS) Index
 ---------------------------------------------------