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Merged
merged 4 commits into from
Oct 15, 2021
Merged

ENH: Add support to save images in WebP format #21274

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6333ea4
Add support to save images in WebP format
kinshukdua Oct 4, 2021
26f1e3f
Add tests for WebP format
kinshukdua Oct 5, 2021
42d2ee4
Fix linting errors in test_agg.py
kinshukdua Oct 11, 2021
394632c
remove dpi pil_kwarg from print_webp
kinshukdua Oct 15, 2021
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2 changes: 2 additions & 0 deletions lib/matplotlib/backend_bases.py
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,7 @@
'svgz': 'Scalable Vector Graphics',
'tif': 'Tagged Image File Format',
'tiff': 'Tagged Image File Format',
'webp': 'WebP Image Format',
}
_default_backends = {
'eps': 'matplotlib.backends.backend_ps',
Expand All @@ -84,6 +85,7 @@
'svgz': 'matplotlib.backends.backend_svg',
'tif': 'matplotlib.backends.backend_agg',
'tiff': 'matplotlib.backends.backend_agg',
'webp': 'matplotlib.backends.backend_agg',
}


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22 changes: 22 additions & 0 deletions lib/matplotlib/backends/backend_agg.py
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Expand Up @@ -594,6 +594,28 @@ def print_tif(self, filename_or_obj, *, pil_kwargs=None):

print_tiff = print_tif

@_check_savefig_extra_args
def print_webp(self, filename_or_obj, *, pil_kwargs=None):
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Are all these pillow save formats the same? If so, I wonder if we just want a generic print_pillow(format=pillow_format) rather than adding these one-by-one?

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As far as I can tell, it is the same for all the fully supported formats- BMP, DDS, DIB, EPS, GIF, ICNS, ICO, IM, JPEG, JPEG 2000, MSP, PCX, PNG, PPM, SGI, SPIDER, TGA, TIFF, WebP, XBM.
I think adding a generic print_pillow does make a lot of sense especially if we want to support all of these formats. The tests however will have to be created for each format, as they all have their specific options that need to be tested.

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Thats the approach I would take, but maybe its more complex than that...

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Maybe we should leave it for a different PR then?

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I guess that depends on whether we think webp is used enough to merit a standalone method.

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I suspect the way we would have to do this in general would be some mild-meta-programming as

matplotlib/lib/matplotlib/backend_bases.py

Line 2250 in a698063

print_method = getattr(canvas, 'print_%s' % format)
is how we look up the method to use and above it we get the format via

matplotlib/lib/matplotlib/backend_bases.py

Lines 2236 to 2246 in a698063

if format is None:
# get format from filename, or from backend's default filetype
if isinstance(filename, os.PathLike):
filename = os.fspath(filename)
if isinstance(filename, str):
format = os.path.splitext(filename)[1][1:]
if format is None or format == '':
format = self.get_default_filetype()
if isinstance(filename, str):
filename = filename.rstrip('.') + '.' + format
format = format.lower()
so we have to have a print_foo method for every format.

However, we can write ourselves a print function factory function and in backend_agg.py do something like:

for fmt in LIST_OF_PILLOW_FORMATS:
   setattr(BackendAgg, f'print_{fmt}', pillow_printer_factor(fmt)

"""
Write the figure to a WebP file.

Parameters
----------
filename_or_obj : str or path-like or file-like
The file to write to.

Other Parameters
----------------
pil_kwargs : dict, optional
Additional keyword arguments that are passed to
`PIL.Image.Image.save` when saving the figure.
"""
FigureCanvasAgg.draw(self)
if pil_kwargs is None:
pil_kwargs = {}
return (Image.fromarray(np.asarray(self.buffer_rgba()))
.save(filename_or_obj, format='webp', **pil_kwargs))


@_Backend.export
class _BackendAgg(_Backend):
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19 changes: 19 additions & 0 deletions lib/matplotlib/tests/test_agg.py
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Expand Up @@ -249,6 +249,25 @@ def test_pil_kwargs_tiff():
assert tags["ImageDescription"] == "test image"


def test_pil_kwargs_webp():
plt.plot([0, 1, 2], [0, 1, 0])
buf_small = io.BytesIO()
pil_kwargs_low = {"quality": 1}
plt.savefig(buf_small, format="webp", pil_kwargs=pil_kwargs_low)
buf_large = io.BytesIO()
pil_kwargs_high = {"quality": 100}
plt.savefig(buf_large, format="webp", pil_kwargs=pil_kwargs_high)
assert buf_large.getbuffer().nbytes > buf_small.getbuffer().nbytes


def test_webp_alpha():
plt.plot([0, 1, 2], [0, 1, 0])
buf = io.BytesIO()
plt.savefig(buf, format="webp", transparent=True)
im = Image.open(buf)
assert im.mode == "RGBA"


def test_draw_path_collection_error_handling():
fig, ax = plt.subplots()
ax.scatter([1], [1]).set_paths(path.Path([(0, 1), (2, 3)]))
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