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FIX: make_image should not modify original array #29892

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Merged
merged 1 commit into from
Apr 13, 2025
Merged

FIX: make_image should not modify original array #29892

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5 changes: 5 additions & 0 deletions lib/matplotlib/image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -439,6 +439,8 @@ def _make_image(self, A, in_bbox, out_bbox, clip_bbox, magnification=1.0,
if not (A.ndim == 2 or A.ndim == 3 and A.shape[-1] in (3, 4)):
raise ValueError(f"Invalid shape {A.shape} for image data")

float_rgba_in = A.ndim == 3 and A.shape[-1] == 4 and A.dtype.kind == 'f'

# if antialiased, this needs to change as window sizes
# change:
interpolation_stage = self._interpolation_stage
Expand Down Expand Up @@ -520,6 +522,9 @@ def _make_image(self, A, in_bbox, out_bbox, clip_bbox, magnification=1.0,
# Resample in premultiplied alpha space. (TODO: Consider
# implementing premultiplied-space resampling in
# span_image_resample_rgba_affine::generate?)
if float_rgba_in and np.ndim(alpha) == 0 and np.any(A[..., 3] < 1):
# Do not modify original RGBA input
A = A.copy()
A[..., :3] *= A[..., 3:]
res = _resample(self, A, out_shape, t)
np.divide(res[..., :3], res[..., 3:], out=res[..., :3],
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27 changes: 27 additions & 0 deletions lib/matplotlib/tests/test_image.py
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Expand Up @@ -281,6 +281,33 @@ def test_imshow_alpha(fig_test, fig_ref):
ax3.imshow(rgbau)


@pytest.mark.parametrize('n_channels, is_int, alpha_arr, opaque',
[(3, False, False, False), # RGB float
(4, False, False, False), # RGBA float
(4, False, True, False), # RGBA float with alpha array
(4, False, False, True), # RGBA float with solid color
(4, True, False, False)]) # RGBA unint8
def test_imshow_multi_draw(n_channels, is_int, alpha_arr, opaque):
if is_int:
array = np.random.randint(0, 256, (2, 2, n_channels))
else:
array = np.random.random((2, 2, n_channels))
if opaque:
array[:, :, 3] = 1

if alpha_arr:
alpha = np.array([[0.3, 0.5], [1, 0.8]])
else:
alpha = None

fig, ax = plt.subplots()
im = ax.imshow(array, alpha=alpha)
fig.draw_without_rendering()

# Draw should not modify original array
np.testing.assert_array_equal(array, im._A)


def test_cursor_data():
from matplotlib.backend_bases import MouseEvent

Expand Down
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