From 897c280064f0986b7e43762dab9c7aa280da62cc Mon Sep 17 00:00:00 2001
From: Roy Smart <roytsmart@gmail.com>
Date: Wed, 15 Nov 2023 23:30:41 -0700
Subject: [PATCH] Added `colorsynth.xyY_from_XYZ_cie()` and
 `colorsynth.XYZ_from_xyY_cie()` functions.

---
 colorsynth/_colorsynth.py            | 46 ++++++++++++++++++++++++++++
 colorsynth/_tests/test_colorsynth.py | 36 +++++++++++++++++-----
 2 files changed, 75 insertions(+), 7 deletions(-)

diff --git a/colorsynth/_colorsynth.py b/colorsynth/_colorsynth.py
index 88da2d6..358f4c9 100644
--- a/colorsynth/_colorsynth.py
+++ b/colorsynth/_colorsynth.py
@@ -9,6 +9,8 @@
     "color_matching_z",
     "color_matching_xyz",
     "cie_1931_tristimulus",
+    "xyY_from_XYZ_cie",
+    "XYZ_from_xyY_cie",
     "srgb",
 ]
 
@@ -322,6 +324,50 @@ def cie_1931_tristimulus(
     return result
 
 
+def xyY_from_XYZ_cie(
+    XYZ: np.ndarray,
+    axis: int = -1,
+) -> np.ndarray:
+    """
+    Convert from a CIE :math:`XYZ` color space to a :math:`xyY` color space
+
+    Parameters
+    ----------
+    XYZ
+        color values in a CIE :math:`XYZ` color space to be converted
+    axis
+        logical axis along which the :math:`XYZ` values are distributed
+    """
+    XYZ_sum = XYZ.sum(axis)
+    X, Y, Z = np.moveaxis(XYZ, source=axis, destination=0)
+    x = X / XYZ_sum
+    y = Y / XYZ_sum
+    result = np.stack([x, y, Y], axis=axis)
+    return result
+
+
+def XYZ_from_xyY_cie(
+    xyY: np.ndarray,
+    axis: int = -1,
+) -> np.ndarray:
+    """
+    Convert from a CIE :math:`xyY` color space to a :math:`XYZ` color space
+
+    Parameters
+    ----------
+    xyY
+        color values in a CIE :math:`xyY` color space to be converted
+    axis
+        logical axis along which the :math:`xyY` values are distributed
+    """
+    x, y, Y = np.moveaxis(xyY, source=axis, destination=0)
+    r = Y / y
+    X = r * x
+    Z = r * (1 - x - y)
+    result = np.stack([X, Y, Z], axis=axis)
+    return result
+
+
 def srgb(
     tristimulus: np.ndarray,
     axis: int = -1,
diff --git a/colorsynth/_tests/test_colorsynth.py b/colorsynth/_tests/test_colorsynth.py
index e252b2a..ac6669f 100644
--- a/colorsynth/_tests/test_colorsynth.py
+++ b/colorsynth/_tests/test_colorsynth.py
@@ -12,6 +12,12 @@
 ]
 
 
+XYZ = [
+    np.random.uniform(size=(3,)),
+    np.random.uniform(size=(64, 64, 3)),
+]
+
+
 @pytest.mark.parametrize(argnames="wavelength", argvalues=wavelengths)
 def test_d65_standard_illuminant(
     wavelength: u.Quantity,
@@ -84,13 +90,29 @@ def test_cie_1931_tristimulus(
     assert result.shape[axis] == 3
 
 
-@pytest.mark.parametrize(
-    argnames="tristimulus",
-    argvalues=[
-        np.random.uniform(size=(3,)),
-        np.random.uniform(size=(64, 64, 3)),
-    ],
-)
+@pytest.mark.parametrize("XYZ", XYZ)
+@pytest.mark.parametrize("axis", [-1])
+def test_xyY_from_XYZ_cie(
+    XYZ: np.ndarray,
+    axis: int,
+):
+    result = colorsynth.xyY_from_XYZ_cie(XYZ, axis=axis)
+    assert isinstance(result, np.ndarray)
+    assert result.shape[axis] == 3
+
+
+@pytest.mark.parametrize("xyY", XYZ)
+@pytest.mark.parametrize("axis", [-1])
+def test_XYZ_from_xyY_cie(
+    xyY: np.ndarray,
+    axis: int,
+):
+    result = colorsynth.XYZ_from_xyY_cie(xyY, axis=axis)
+    assert isinstance(result, np.ndarray)
+    assert result.shape[axis] == 3
+
+
+@pytest.mark.parametrize("tristimulus", XYZ,)
 @pytest.mark.parametrize(argnames="axis", argvalues=[-1])
 def test_srgb(
     tristimulus: np.ndarray,