ENH: Add support to save images in WebP format by kinshukdua · Pull Request #21274 · matplotlib/matplotlib · GitHub

PR Summary

Fixes #21162
This adds support to save images in WebP format.
This works fine without any problem since Pillow supports WebP and the code is analogous to the support for tiff images added in PR #15193.

PR Checklist

Has pytest style unit tests (and pytest passes).
Is Flake 8 compliant (run flake8 on changed files to check).
[N/A] New features are documented, with examples if plot related.
Documentation is sphinx and numpydoc compliant (the docs should build without error).
Conforms to Matplotlib style conventions (install flake8-docstrings and run flake8 --docstring-convention=all).
[N/A] New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
[N/A] API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).

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It is nice how simple this patch is to pick up a new format!

Could you add a test that saves an image to ByteIO buffer? That will be enough to exercise the code that you added. Given that this is using the Agg backend we definitely do not need to run it against the full test suite as we would then just be testing pillow. It looks like print_tiff is covered, maybe find that test and adapt / parameterize it?

@tacaswell Yes, I will add a test using ByteIO buffer.

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?

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.

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

Maybe we should leave it for a different PR then?

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

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)

@kinshukdua Would you be willing to rebase this PR? We prefer to not merge the default branch back into feature branches.

@tacaswell I've rebased the PR, I'm new to git so please let me know if I need to do something else.

I think we need to decide whether we want a new webp method, a general "pass to pillow" method or a factory. If in the end, we don't want a new webp method, I dont think we can add this.

I'm not against a webp method if it really is something many folks want, but it seems obscure to me, and maybe just a general method to pillow takes care of the obscure use cases.

I'm blocking until we can sort this out, but if another core dev wants to support a standalone webp method, feel free to dismiss my review.

@tacaswell said that this is what we want, which is fine with me. Thanks for your patience!

Please consider clarifying the situation wrt. dpi. Anyone can dismiss this.

Thanks, anyone can merge after CI passes. Congrats on getting your first PR in :)

Thanks @kinshukdua! Congratulations on your first PR to Matplotlib 🎉 We hope to hear from you again.

Thanks! It was really great contributing back to such an important open source project, I hope to continue contributing.

ENH: Add support to save images in WebP format

Add support to save images in WebP format

6333ea4

github-actions Bot reviewed Oct 4, 2021

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tacaswell added this to the v3.6.0 milestone Oct 4, 2021

Add tests for WebP format

26f1e3f

jklymak reviewed Oct 5, 2021

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Fix linting errors in test_agg.py

42d2ee4

timhoffm approved these changes Oct 11, 2021

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jklymak requested changes Oct 12, 2021

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jklymak approved these changes Oct 12, 2021

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anntzer reviewed Oct 12, 2021

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Comment thread lib/matplotlib/backends/backend_agg.py Outdated

anntzer requested changes Oct 12, 2021

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remove dpi pil_kwarg from print_webp

394632c

anntzer approved these changes Oct 15, 2021

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QuLogic merged commit 60466fb into matplotlib:master Oct 15, 2021

anntzer mentioned this pull request Oct 18, 2021

Factor common parts of saving to different formats using pillow. #21376

Merged

7 tasks

tacaswell pushed a commit that referenced this pull request Oct 20, 2021

Merge pull request #21274 from kinshukdua/master

f66c626

ENH: Add support to save images in WebP format

QuLogic mentioned this pull request Sep 9, 2022

Consolidate release notes for 3.6 #23814

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2 tasks done

timhoffm mentioned this pull request Jul 16, 2025

[ENH]: Support avif as output format #28809

Closed

joshuacwnewton mentioned this pull request Nov 7, 2025

Blank page when opening QC report with many rows spinalcordtoolbox/spinalcordtoolbox#5083

Closed

                   print_tiff = print_tif
+                  @_check_savefig_extra_args
+                  def print_webp(self, filename_or_obj, *, pil_kwargs=None):

	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()

ENH: Add support to save images in WebP format by kinshukdua · Pull Request #21274 · matplotlib/matplotlib · GitHub

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

ENH: Add support to save images in WebP format#21274QuLogic merged 4 commits intomatplotlib:mastermatplotlib/matplotlib:masterfrom kinshukdua:masterCopy head branch name to clipboard

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kinshukdua commented Oct 4, 2021

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ENH: Add support to save images in WebP format#21274
QuLogic merged 4 commits into
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