8000 Backport PR #12062: Separate alpha and rbg interpolation then recombi… · matplotlib/matplotlib@da1245f · GitHub
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Backport PR #12062: Separate alpha and rbg interpolation then recombine to fix issue11316
1 parent 334d875 commit da1245f

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7 files changed

+65
-41
lines changed

7 files changed

+65
-41
lines changed

‎lib/matplotlib/image.py

Lines changed: 17 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -489,16 +489,31 @@ def _make_image(self, A, in_bbox, out_bbox, clip_bbox, magnification=1.0,
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.format(A.shape))
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output = np.zeros((out_height, out_width, 4), dtype=A.dtype)
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output_a = np.zeros((out_height, out_width), dtype=A.dtype)
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alpha = self.get_alpha()
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if alpha is None:
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alpha = 1.0
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alpha = 1
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#resample alpha channel
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alpha_channel = A[..., 3]
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_image.resample(
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alpha_channel, output_a, t,
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_interpd_[self.get_interpolation()],
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self.get_resample(), alpha,
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self.get_filternorm(), self.get_filterrad())
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#resample rgb channels
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A = _rgb_to_rgba(A[..., :3])
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_image.resample(
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A, output, t, _interpd_[self.get_interpolation()],
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A, output, t,
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_interpd_[self.get_interpolation()],
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self.get_resample(), alpha,
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self.get_filternorm(), self.get_filterrad())
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#recombine rgb and alpha channels
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output[..., 3] = output_a
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# at this point output is either a 2D array of normed data
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# (of int or float)
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# or an RGBA array of re-sampled input

‎lib/matplotlib/tests/baseline_images/test_image/image_composite_alpha.pdf

-22.6 KB
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‎lib/matplotlib/tests/baseline_images/test_image/image_composite_alpha.png

-3.72 KB
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‎lib/matplotlib/tests/baseline_images/test_image/image_composite_alpha.svg

Lines changed: 34 additions & 39 deletions
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‎lib/matplotlib/tests/baseline_images/test_image/interp_alpha.png

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‎lib/matplotlib/tests/baseline_images/test_png/pngsuite.png

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‎lib/matplotlib/tests/test_image.py

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -45,6 +45,20 @@ def test_image_interps():
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ax3.set_ylabel('bicubic')
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48+
@image_comparison(baseline_images=['interp_alpha'],
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extensions=['png'], remove_text=True)
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def test_alpha_interp():
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'Test the interpolation of the alpha channel on RGBA images'
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fig, (axl, axr) = plt.subplots(1, 2)
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# full green image
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img = np.zeros((5, 5, 4))
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img[..., 1] = np.ones((5, 5))
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# transparent under main diagonal
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img[..., 3] = np.tril(np.ones((5, 5), dtype=np.uint8))
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axl.imshow(img, interpolation="none")
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axr.imshow(img, interpolation="bilinear")
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@image_comparison(baseline_images=['interp_nearest_vs_none'],
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extensions=['pdf', 'svg'], remove_text=True)
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def test_interp_nearest_vs_none():

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