added support for YDbDr (#3018)

* added support for YDbDr
* added ydbdr to colorspace tests

skimage/color/__init__.py

@@ -31,6 +31,8 @@
                         ypbpr2rgb,
                         rgb2ycbcr,
                         ycbcr2rgb,
+                        rgb2ydbdr,
+                        ydbdr2rgb,
                         separate_stains,
                         combine_stains,
                         rgb_from_hed,
@@ -93,6 +95,8 @@
            'ypbpr2rgb',
            'rgb2ycbcr',
            'ycbcr2rgb',
+           'rgb2ydbdr',
+           'ydbdr2rgb',
            'separate_stains',
            'combine_stains',
            'rgb_from_hed',

skimage/color/colorconv.py

@@ -98,9 +98,11 @@ def convert_colorspace(arr, fromspace, tospace):
     ----------
     arr : array_like
         The image to convert.
-    fromspace : {'RGB', 'HSV', 'RGB CIE', 'XYZ', 'YUV', 'YIQ', 'YPbPr', 'YCbCr'}
+    fromspace : {'RGB', 'HSV', 'RGB CIE', 'XYZ', 'YUV',
+                 'YIQ', 'YPbPr', 'YCbCr', 'YDbDr'}
         The color space to convert from. Can be specified in lower case.
-    tospace : {'RGB', 'HSV', 'RGB CIE', 'XYZ', 'YUV', 'YIQ', 'YPbPr', 'YCbCr'}
+    tospace : {'RGB', 'HSV', 'RGB CIE', 'XYZ', 'YUV',
+               'YIQ', 'YPbPr', 'YCbCr', 'YDbDr'}
         The color space to convert to. Can be specified in lower case.
 
     Returns
@@ -122,10 +124,10 @@ def convert_colorspace(arr, fromspace, tospace):
     """
     fromdict = {'rgb': lambda im: im, 'hsv': hsv2rgb, 'rgb cie': rgbcie2rgb,
                 'xyz': xyz2rgb, 'yuv': yuv2rgb, 'yiq': yiq2rgb,
-                'ypbpr': ypbpr2rgb, 'ycbcr': ycbcr2rgb}
+                'ypbpr': ypbpr2rgb, 'ycbcr': ycbcr2rgb, 'ydbdr': ydbdr2rgb}
     todict = {'rgb': lambda im: im, 'hsv': rgb2hsv, 'rgb cie': rgb2rgbcie,
               'xyz': rgb2xyz, 'yuv': rgb2yuv, 'yiq': rgb2yiq,
-              'ypbpr': rgb2ypbpr, 'ycbcr': rgb2ycbcr}
+              'ypbpr': rgb2ypbpr, 'ycbcr': rgb2ycbcr, 'ydbdr': rgb2ydbdr}
 
     fromspace = fromspace.lower()
     tospace = tospace.lower()
@@ -405,6 +407,13 @@ def hsv2rgb(hsv):
 
 rgb_from_ycbcr = linalg.inv(ycbcr_from_rgb)
 
+ydbdr_from_rgb = np.array([[    0.299,   0.587,    0.114],
+                           [   -0.45 ,  -0.883,    1.333],
+                           [   -1.333,   1.116,    0.217]])
+
+rgb_from_ydbdr = linalg.inv(ydbdr_from_rgb)
+
+
 # CIE LAB constants for Observer=2A, Illuminant=D65
 # NOTE: this is actually the XYZ values for the illuminant above.
 lab_ref_white = np.array([0.95047, 1., 1.08883])
@@ -1692,6 +1701,40 @@ def rgb2ycbcr(rgb):
     return arr
 
 
+def rgb2ydbdr(rgb):
+    """RGB to YDbDr color space conversion.
+
+    Parameters
+    ----------
+    rgb : array_like
+        The image in RGB format, in a 3- or 4-D array of shape
+        ``(M, N, [P,] 3)``.
+
+    Returns
+    -------
+    out : ndarray
+        The image in YDbDr format, in a 3- or 4-D array of shape
+        ``(M, N, [P,] 3)``.
+
+    Raises
+    ------
+    ValueError
+        If `rgb` is not a 3- or 4-D array of shape ``(M, N, [P,] 3)``.
+
+    Notes
+    -----
+    This is the color space which is commonly used
+    by video codecs, it is also the reversible color transform in JPEG2000.
+
+    References
+    ----------
+    .. [1] https://en.wikipedia.org/wiki/YDbDr
+
+    """
+    arr = _convert(ydbdr_from_rgb, rgb)
+    return arr
+
+
 def yuv2rgb(yuv):
     """YUV to RGB color space conversion.
 
@@ -1806,3 +1849,37 @@ def ycbcr2rgb(ycbcr):
     arr[..., 1] -= 128
     arr[..., 2] -= 128
     return _convert(rgb_from_ycbcr, arr)
+
+
+def ydbdr2rgb(ydbdr):
+    """YDbDr to RGB color space conversion.
+
+    Parameters
+    ----------
+    ydbdr : array_like
+        The image in YDbDr format, in a 3- or 4-D array of shape
+        ``(M, N, [P,] 3)``.
+
+    Returns
+    -------
+    out : ndarray
+        The image in RGB format, in a 3- or 4-D array of shape
+        ``(M, N, [P,] 3)``.
+
+    Raises
+    ------
+    ValueError
+        If `ydbdr` is not a 3- or 4-D array of shape ``(M, N, [P,] 3)``.
+
+    Notes
+    -----
+    This is the color space which is commonly used
+    by video codecs, it is also the reversible color transform in JPEG2000.
+
+    References
+    ----------
+    .. [1] https://en.wikipedia.org/wiki/YDbDr
+
+    """
+    arr = ydbdr.copy()
+    return _convert(rgb_from_ydbdr, arr)

skimage/color/tests/test_colorconv.py

@@ -38,6 +38,7 @@
                            rgb2yiq, yiq2rgb,
                            rgb2ypbpr, ypbpr2rgb,
                            rgb2ycbcr, ycbcr2rgb,
+                           rgb2ydbdr, ydbdr2rgb,
                            rgba2rgb,
                            guess_spatial_dimensions)
 
@@ -221,9 +222,15 @@ def test_rgbcie2rgb_conversion(self):
                             self.colbars_array)
 
     def test_convert_colorspace(self):
-        colspaces = ['HSV', 'RGB CIE', 'XYZ', 'YCbCr', 'YPbPr']
-        colfuncs_from = [hsv2rgb, rgbcie2rgb, xyz2rgb, ycbcr2rgb, ypbpr2rgb]
-        colfuncs_to = [rgb2hsv, rgb2rgbcie, rgb2xyz, rgb2ycbcr, rgb2ypbpr]
+        colspaces = ['HSV', 'RGB CIE', 'XYZ', 'YCbCr', 'YPbPr', 'YDbDr']
+        colfuncs_from = [
+            hsv2rgb, rgbcie2rgb, xyz2rgb,
+            ycbcr2rgb, ypbpr2rgb, ydbdr2rgb
+        ]
+        colfuncs_to = [
+            rgb2hsv, rgb2rgbcie, rgb2xyz,
+            rgb2ycbcr, rgb2ypbpr, rgb2ydbdr
+        ]
 
         assert_almost_equal(
             convert_colorspace(self.colbars_array, 'RGB', 'RGB'),
@@ -467,18 +474,21 @@ def test_yuv(self):
         assert_array_almost_equal(rgb2yiq(rgb), np.array([[[1, 0, 0]]]))
         assert_array_almost_equal(rgb2ypbpr(rgb), np.array([[[1, 0, 0]]]))
         assert_array_almost_equal(rgb2ycbcr(rgb), np.array([[[235, 128, 128]]]))
+        assert_array_almost_equal(rgb2ydbdr(rgb), np.array([[[1, 0, 0]]]))
         rgb = np.array([[[0.0, 1.0, 0.0]]])
         assert_array_almost_equal(rgb2yuv(rgb), np.array([[[0.587, -0.28886916, -0.51496512]]]))
         assert_array_almost_equal(rgb2yiq(rgb), np.array([[[0.587, -0.27455667, -0.52273617]]]))
         assert_array_almost_equal(rgb2ypbpr(rgb), np.array([[[0.587, -0.331264, -0.418688]]]))
         assert_array_almost_equal(rgb2ycbcr(rgb), np.array([[[144.553,   53.797,   34.214]]]))
+        assert_array_almost_equal(rgb2ydbdr(rgb), np.array([[[0.587, -0.883, 1.116]]]))
 
     def test_yuv_roundtrip(self):
         img_rgb = img_as_float(self.img_rgb)[::16, ::16]
         assert_array_almost_equal(yuv2rgb(rgb2yuv(img_rgb)), img_rgb)
         assert_array_almost_equal(yiq2rgb(rgb2yiq(img_rgb)), img_rgb)
         assert_array_almost_equal(ypbpr2rgb(rgb2ypbpr(img_rgb)), img_rgb)
         assert_array_almost_equal(ycbcr2rgb(rgb2ycbcr(img_rgb)), img_rgb)
+        assert_array_almost_equal(ydbdr2rgb(rgb2ydbdr(img_rgb)), img_rgb)
 
     def test_rgb2yiq_conversion(self):
         rgb = img_as_float(self.img_rgb)[::16, ::16]