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Improve handling of alpha when saving to jpeg. #15437

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Mar 24, 2020
Merged

Improve handling of alpha when saving to jpeg. #15437

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18 changes: 10 additions & 8 deletions lib/matplotlib/backends/backend_agg.py
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Original file line number Diff line number Diff line change
Expand Up @@ -563,23 +563,25 @@ def print_jpg(self, filename_or_obj, *args, dryrun=False, pil_kwargs=None,
`PIL.Image.save` when saving the figure. These take precedence
over *quality*, *optimize* and *progressive*.
"""
FigureCanvasAgg.draw(self)
# Remove transparency by alpha-blending on an assumed white background.
r, g, b, a = mcolors.to_rgba(self.figure.get_facecolor())
try:
self.figure.set_facecolor(a * np.array([r, g, b]) + 1 - a)
FigureCanvasAgg.draw(self)
finally:
self.figure.set_facecolor((r, g, b, a))
if dryrun:
return
# The image is "pasted" onto a white background image to safely
# handle any transparency
image = Image.fromarray(np.asarray(self.buffer_rgba()))
background = Image.new("RGB", image.size, "white")
background.paste(image, image)
if pil_kwargs is None:
pil_kwargs = {}
for k in ["quality", "optimize", "progressive"]:
if k in kwargs:
pil_kwargs.setdefault(k, kwargs[k])
pil_kwargs.setdefault("quality", rcParams["savefig.jpeg_quality"])
pil_kwargs.setdefault("dpi", (self.figure.dpi, self.figure.dpi))
return background.save(
filename_or_obj, format='jpeg', **pil_kwargs)
# Drop alpha channel now.
return (Image.fromarray(np.asarray(self.buffer_rgba())[..., :3])
.save(filename_or_obj, format='jpeg', **pil_kwargs))

print_jpeg = print_jpg

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