Merge pull request matplotlib#26096 from greglucas/sm-masked-rgba

FIX: Handle masked arrays for RGBA input with ScalarMappables

Author: rcomer

doc/api/next_api_changes/behavior/26096-GL.rst

@@ -0,0 +1,4 @@
+``ScalarMappable.to_rgba()`` now respects the mask of RGB(A) arrays
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Previously, the mask was ignored. Now the alpha channel is set to 0 if any
+component (R, G, B, or A) is masked.

lib/matplotlib/cm.py

@@ -450,7 +450,7 @@ def to_rgba(self, x, alpha=None, bytes=False, norm=True):
         treated as an RGB or RGBA array, and no mapping will be done.
         The array can be `~numpy.uint8`, or it can be floats with
         values in the 0-1 range; otherwise a ValueError will be raised.
-        If it is a masked array, the mask will be ignored.
+        If it is a masked array, any masked elements will be set to 0 alpha.
         If the last dimension is 3, the *alpha* kwarg (defaulting to 1)
         will be used to fill in the transparency.  If the last dimension
         is 4, the *alpha* kwarg is ignored; it does not
@@ -493,6 +493,10 @@ def to_rgba(self, x, alpha=None, bytes=False, norm=True):
                 else:
                     raise ValueError("Image RGB array must be uint8 or "
                                      "floating point; found %s" % xx.dtype)
+                # Account for any masked entries in the original array
+                # If any of R, G, B, or A are masked for an entry, we set alpha to 0
+                if np.ma.is_masked(x):
+                    xx[np.any(np.ma.getmaskarray(x), axis=2), 3] = 0
                 return xx
         except AttributeError:
             # e.g., x is not an ndarray; so try mapping it

lib/matplotlib/tests/test_colors.py

@@ -1353,6 +1353,48 @@ def test_to_rgba_error_with_color_invalid_alpha_tuple():
         mcolors.to_rgba(('blue', 2.0))
 
 
+@pytest.mark.parametrize("bytes", (True, False))
+def test_scalarmappable_to_rgba(bytes):
+    sm = cm.ScalarMappable()
+    alpha_1 = 255 if bytes else 1
+
+    # uint8 RGBA
+    x = np.ones((2, 3, 4), dtype=np.uint8)
+    expected = x.copy() if bytes else x.astype(np.float32)/255
+    np.testing.assert_array_equal(sm.to_rgba(x, bytes=bytes), expected)
+    # uint8 RGB
+    expected[..., 3] = alpha_1
+    np.testing.assert_array_equal(sm.to_rgba(x[..., :3], bytes=bytes), expected)
+    # uint8 masked RGBA
+    xm = np.ma.masked_array(x, mask=np.zeros_like(x))
+    xm.mask[0, 0, 0] = True
+    expected = x.copy() if bytes else x.astype(np.float32)/255
+    expected[0, 0, 3] = 0
+    np.testing.assert_array_equal(sm.to_rgba(xm, bytes=bytes), expected)
+    # uint8 masked RGB
+    expected[..., 3] = alpha_1
+    expected[0, 0, 3] = 0
+    np.testing.assert_array_equal(sm.to_rgba(xm[..., :3], bytes=bytes), expected)
+
+    # float RGBA
+    x = np.ones((2, 3, 4), dtype=float) * 0.5
+    expected = (x * 255).astype(np.uint8) if bytes else x.copy()
+    np.testing.assert_array_equal(sm.to_rgba(x, bytes=bytes), expected)
+    # float RGB
+    expected[..., 3] = alpha_1
+    np.testing.assert_array_equal(sm.to_rgba(x[..., :3], bytes=bytes), expected)
+    # float masked RGBA
+    xm = np.ma.masked_array(x, mask=np.zeros_like(x))
+    xm.mask[0, 0, 0] = True
+    expected = (x * 255).astype(np.uint8) if bytes else x.copy()
+    expected[0, 0, 3] = 0
+    np.testing.assert_array_equal(sm.to_rgba(xm, bytes=bytes), expected)
+    # float masked RGB
+    expected[..., 3] = alpha_1
+    expected[0, 0, 3] = 0
+    np.testing.assert_array_equal(sm.to_rgba(xm[..., :3], bytes=bytes), expected)
+
+
 def test_failed_conversions():
     with pytest.raises(ValueError):
         mcolors.to_rgba('5')