Merge pull request #85 from colour-science/feature/bt2020

Implement support for "ITU-R BT.2020" colorspace.

colormath/color_conversions.py

@@ -17,7 +17,8 @@
 from colormath import spectral_constants
 from colormath.color_objects import ColorBase, XYZColor, sRGBColor, \
     LCHabColor, LCHuvColor, LabColor, xyYColor, LuvColor, HSVColor, HSLColor, \
-    CMYColor, CMYKColor, BaseRGBColor, IPTColor, SpectralColor, AdobeRGBColor
+    CMYColor, CMYKColor, BaseRGBColor, IPTColor, SpectralColor, AdobeRGBColor, \
+    BT2020Color
 from colormath.chromatic_adaptation import apply_chromatic_adaptation
 from colormath.color_exceptions import InvalidIlluminantError, \
     UndefinedConversionError
@@ -520,6 +521,17 @@ def XYZ_to_RGB(cobj, target_rgb, *args, **kwargs):
                 nonlinear_channels[channel] = v * 12.92
             else:
                 nonlinear_channels[channel] = 1.055 * math.pow(v, 1 / 2.4) - 0.055
+    elif target_rgb == BT2020Color:
+        if kwargs.get('is_12_bits_system'):
+            a, b = 1.0993, 0.0181
+        else:
+            a, b = 1.099, 0.018
+        for channel in ['r', 'g', 'b']:
+            v = linear_channels[channel]
+            if v < b:
+                nonlinear_channels[channel] = v * 4.5
+            else:
+                nonlinear_channels[channel] = a * math.pow(v, 0.45) - (a - 1)
     else:
         # If it's not sRGB...
         for channel in ['r', 'g', 'b']:
@@ -548,6 +560,17 @@ def RGB_to_XYZ(cobj, target_illuminant=None, *args, **kwargs):
                 linear_channels[channel] = V / 12.92
             else:
                 linear_channels[channel] = math.pow((V + 0.055) / 1.055, 2.4)
+    elif isinstance(cobj, BT2020Color):
+        if kwargs.get('is_12_bits_system'):
+            a, b, c = 1.0993, 0.0181, 0.081697877417347
+        else:
+            a, b, c = 1.099, 0.018, 0.08124794403514049
+        for channel in ['r', 'g', 'b']:
+            V = getattr(cobj, 'rgb_' + channel)
+            if V <= c:
+                linear_channels[channel] = V / 4.5
+            else:
+                linear_channels[channel] = math.pow((V + (a - 1)) / a, 1 / 0.45)
     else:
         # If it's not sRGB...
         gamma = cobj.rgb_gamma

colormath/color_objects.py

@@ -634,6 +634,39 @@ class sRGBColor(BaseRGBColor):
     }
 
 
+class BT2020Color(BaseRGBColor):
+    """
+    Represents a ITU-R BT.2020 color.
+
+    .. note:: If you pass in upscaled values, we automatically scale them
+        down to 0.0-1.0. If you need the old upscaled values, you can
+        retrieve them with :py:meth:`get_upscaled_value_tuple`.
+
+    :ivar float rgb_r: R coordinate
+    :ivar float rgb_g: G coordinate
+    :ivar float rgb_b: B coordinate
+    :ivar bool is_upscaled: If True, RGB values are between 1-255. If False,
+        0.0-1.0.
+    """
+
+    #: RGB space's gamma constant.
+    rgb_gamma = 2.4
+    #: The RGB space's native illuminant. Important when converting to XYZ.
+    native_illuminant = "d65"
+    conversion_matrices = {
+        "xyz_to_rgb":
+            numpy.array((
+                (1.716651187971269, -0.355670783776393, -0.253366281373660),
+                (-0.666684351832489, 1.616481236634939, 0.015768545813911),
+                (0.017639857445311, -0.042770613257809, 0.942103121235474))),
+        "rgb_to_xyz":
+            numpy.array((
+                (0.636958048301291, 0.144616903586208, 0.168880975164172),
+                (0.262700212011267, 0.677998071518871, 0.059301716469862),
+                (0.000000000000000, 0.028072693049087, 1.060985057710791))),
+    }
+
+
 class AdobeRGBColor(BaseRGBColor):
     """
     Represents an Adobe RGB color.

doc_src/color_objects.rst

@@ -48,6 +48,11 @@ sRGBColor
 
 .. autoclass:: colormath.color_objects.sRGBColor
 
+BT2020Color
+-----------
+
+.. autoclass:: colormath.color_objects.BT2020Color
+
 AdobeRGBColor
 -------------
 

tests/test_color_conversion.py

@@ -1,10 +1,13 @@
 # -*- coding: utf-8 -*-
 import itertools
+import numpy as np
 import unittest
 from colormath import color_conversions
-from colormath.color_conversions import GraphConversionManager, XYZ_to_RGB, HSV_to_RGB
+from colormath.color_conversions import GraphConversionManager, XYZ_to_RGB, HSV_to_RGB, \
+                                        RGB_to_XYZ
 from colormath.color_exceptions import UndefinedConversionError
-from colormath.color_objects import XYZColor, BaseRGBColor, HSVColor, HSLColor
+from colormath.color_objects import XYZColor, BaseRGBColor, HSVColor, HSLColor, \
+                                    AdobeRGBColor, BT2020Color, sRGBColor
 
 
 class GraphConversionManagerTestCase(unittest.TestCase):
@@ -52,3 +55,17 @@ def test_conversion_validity(self):
                 # Otherwise check that all the conversion functions math up
                 for a, b in zip(path[:-1], path[1:]):
                     self.assertEqual(a.target_type, b.start_type)
+
+    def test_transfer_functions(self):
+        """
+        Tests the transfer functions of the various RGB colorspaces.
+        """
+
+        for colorspace in (AdobeRGBColor, BT2020Color, sRGBColor):
+            for a in (0.0, 0.01, 0.18, 1.0):
+                RGB = [a] * 3
+            np.testing.assert_allclose(
+                XYZ_to_RGB(RGB_to_XYZ(colorspace(*RGB)), colorspace).get_value_tuple(),
+                RGB,
+                rtol=1e-5,
+                atol=1e-5)