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FIX: Handle masked arrays for RGBA input with ScalarMappables #26096

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merged 1 commit into from
Jun 10, 2023
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FIX: Handle masked arrays for RGBA input with ScalarMappables #26096

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4 changes: 4 additions & 0 deletions doc/api/next_api_changes/behavior/26096-GL.rst
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Original file line number Diff line number Diff line change
@@ -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.
6 changes: 5 additions & 1 deletion lib/matplotlib/cm.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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
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42 changes: 42 additions & 0 deletions lib/matplotlib/tests/test_colors.py
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Expand Up @@ -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')
Expand Down