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Tests #29300 black corners when rotating RGB images #29887

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41 changes: 41 additions & 0 deletions lib/matplotlib/tests/test_image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -281,6 +281,47 @@ def test_imshow_alpha(fig_test, fig_ref):
ax3.imshow(rgbau)


def test_rotated_image_corners_no_black():
rng = np.random.default_rng(42)
img = rng.random((100, 20, 3))

fig, ax = plt.subplots()

tr_rotate = Affine2D().rotate_deg_around(10, 50, 45)
tr_translate = Affine2D().translate(250, 250)

ax.imshow(img, transform=tr_rotate + ax.transData, clip_on=False)
ax.imshow(img, transform=tr_translate + ax.transData, clip_on=False)

ax.set_xlim(-250, 500)
ax.set_ylim(-250, 500)

fig.canvas.draw()

# Get the RGB image buffer from the Agg backend
rendered = np.asarray(fig.canvas.buffer_rgba())[:, :, :3] # Drop alpha

plt.close(fig)

corner_size = 50
inset = 5

corners = {
"top-left": rendered[inset:inset+corner_size, inset:inset+corner_size],
"top-right": rendered[inset:inset+corner_size, -inset-corner_size:-inset],
"bottom-left": rendered[-inset-corner_size:-inset, inset:inset+corner_size],
"bottom-right": rendered[-inset-corner_size:-inset, -inset-corner_size:-inset]
}

threshold = 5
for name, corner in corners.items():
is_blackish = np.all(corner < threshold, axis=-1)
percent_black = np.sum(is_blackish) / is_blackish.size
assert percent_black < 0.01, (
f"Too many black pixels in {name} corner: {percent_black:.2%}"
)


def test_cursor_data():
from matplotlib.backend_bases import MouseEvent

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