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FIX: fix anti-aliasing zoom bug #15519

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Merged
merged 1 commit into from
Oct 25, 2019
Merged

FIX: fix anti-aliasing zoom bug #15519

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10 changes: 4 additions & 6 deletions lib/matplotlib/image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -176,11 +176,10 @@ def _resample(
if interpolation == 'antialiased':
# don't antialias if upsampling by an integer number or
# if zooming in more than a factor of 3
shape = list(data.shape)
if image_obj.origin == 'upper':
shape[0] = 0
dispx, dispy = transform.transform([shape[1], shape[0]])

pos = np.array([[0, 0], [data.shape[1], data.shape[0]]])
disp = transform.transform(pos)
dispx = np.abs(np.diff(disp[:, 0]))
dispy = np.abs(np.diff(disp[:, 1]))
if ((dispx > 3 * data.shape[1] or
dispx == data.shape[1] or
dispx == 2 * data.shape[1]) and
Expand All @@ -190,7 +189,6 @@ def _resample(
interpolation = 'nearest'
else:
interpolation = 'hanning'

out = np.zeros(out_shape + data.shape[2:], data.dtype) # 2D->2D, 3D->3D.
if resample is None:
resample = image_obj.get_resample()
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18 changes: 18 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 @@ -198,6 +198,24 @@ def test_imshow_upsample3(fig_test, fig_ref):
axs.imshow(A, interpolation='nearest')


@check_figures_equal(extensions=['png'])
def test_imshow_zoom(fig_test, fig_ref):
# should be less than 3 upsample, so should be nearest...
np.random.seed(19680801)
dpi = 100
A = np.random.rand(int(dpi * 3), int(dpi * 3))
for fig in [fig_test, fig_ref]:
fig.set_size_inches(2.9, 2.9)
axs = fig_test.subplots()
axs.imshow(A, interpolation='nearest')
axs.set_xlim([10, 20])
axs.set_ylim([10, 20])
axs = fig_ref.subplots()
axs.imshow(A, interpolation='antialiased')
axs.set_xlim([10, 20])
axs.set_ylim([10, 20])


@check_figures_equal()
def test_imshow_pil(fig_test, fig_ref):
style.use("default")
Expand Down