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Avoid in-place multiplication of a large value to an array with small integer dtype #8867

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merged 7 commits into from
Mar 29, 2024
Merged

Avoid in-place multiplication of a large value to an array with small integer dtype #8867

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decb4cf
Avoid inplace multiplication
Illviljan Mar 22, 2024
39c3cf8
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Mar 22, 2024
b0fca37
Update test_plot.py
Illviljan Mar 22, 2024
adc945a
Update test_plot.py
Illviljan Mar 23, 2024
1ac134d
Update dataarray_plot.py
Illviljan Mar 23, 2024
be1a0d0
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Mar 23, 2024
4db9d46
Merge branch 'main' into imshow_alpha_inplace_multiplication
Illviljan Mar 26, 2024
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5 changes: 3 additions & 2 deletions xarray/plot/dataarray_plot.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1848,9 +1848,10 @@ def _center_pixels(x):
# missing data transparent. We therefore add an alpha channel if
# there isn't one, and set it to transparent where data is masked.
if z.shape[-1] == 3:
alpha = np.ma.ones(z.shape[:2] + (1,), dtype=z.dtype)
safe_dtype = np.promote_types(z.dtype, np.uint8)
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@Illviljan Illviljan Mar 26, 2024 •
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The dtype should allow at least 0 and 255. But it will be converted in np.ma.concatenate at some point anyway so I thought it's best to just figure it out early and initialize alpha correctly.

alpha = np.ma.ones(z.shape[:2] + (1,), dtype=safe_dtype)
if np.issubdtype(z.dtype, np.integer):
alpha *= 255
alpha[:] = 255
z = np.ma.concatenate((z, alpha), axis=2)
else:
z = z.copy()
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12 changes: 7 additions & 5 deletions xarray/tests/test_plot.py
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Expand Up @@ -2028,15 +2028,17 @@ def test_normalize_rgb_one_arg_error(self) -> None:
for vmin2, vmax2 in ((-1.2, -1), (2, 2.1)):
da.plot.imshow(vmin=vmin2, vmax=vmax2)

def test_imshow_rgb_values_in_valid_range(self) -> None:
da = DataArray(np.arange(75, dtype="uint8").reshape((5, 5, 3)))
@pytest.mark.parametrize("dtype", [np.uint8, np.int8, np.int16])
def test_imshow_rgb_values_in_valid_range(self, dtype) -> None:
da = DataArray(np.arange(75, dtype=dtype).reshape((5, 5, 3)))
_, ax = plt.subplots()
out = da.plot.imshow(ax=ax).get_array()
assert out is not None
dtype = out.dtype
assert dtype is not None
assert dtype == np.uint8
actual_dtype = out.dtype
assert actual_dtype is not None
assert actual_dtype == np.uint8
assert (out[..., :3] == da.values).all() # Compare without added alpha
assert (out[..., -1] == 255).all() # Compare alpha

@pytest.mark.filterwarnings("ignore:Several dimensions of this array")
def test_regression_rgb_imshow_dim_size_one(self) -> None:
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