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Add rasterized option to contourf #29582

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Merged
merged 8 commits into from
Mar 18, 2025
Merged

Add rasterized option to contourf #29582

merged 8 commits into from
Mar 18, 2025

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AdamOrmondroyd
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@AdamOrmondroyd AdamOrmondroyd commented Feb 5, 2025 •
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PR summary

Hi, this is my first PR to matplotlib!

The rasterization documentation suggests one can add rasterized=True to contourf, similar to pcolormesh. This doesn't do anything besides warn the user the kwarg hasn't been used. Setting the resulting QuadContourSet to rasterised causes another warning, but seems to work fine. #27669 picks up on this.

This PR addresses both issues, still need to add tests.

import matplotlib.pyplot as plt
import numpy as np

x = y = np.arange(-3.0, 3.01, delta)
X, Y = np.meshgrid(x, y)
Z = np.exp(-X**2 - Y**2)

fig, ax = plt.subplots(layout='constrained')

CS = ax.contourf(X, Y, Z, 10, rasterized=True)
# currently causes UserWarning: The following kwargs were not used by contour: 'rasterized'
# result isn't rasterized

# or
CS = plt.contourf(X, Y, Z, 10)
CS.set_rasterized(True)
# currently causes UserWarning: Rasterization of '<matplotlib.contour.QuadContourSet object at 0x10304e3c0>' will be ignored
# result is rasterized
fig.savefig('foo.pdf')

(screenshot of) unrasterized foo.pdf
Screenshot 2025-02-05 at 19 16 54
(screenshot of) rasterized foo.pdf
Screenshot 2025-02-05 at 19 15 38

Closes #27669

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@AdamOrmondroyd AdamOrmondroyd mentioned this pull request Feb 5, 2025
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Thank you for opening your first PR into Matplotlib!

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I've had a good look and can't see where the test for this would naturally fit in

@AdamOrmondroyd AdamOrmondroyd marked this pull request as ready for review February 9, 2025 14:29
rcomer
rcomer reviewed Mar 2, 2025
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Thanks @AdamOrmondroyd and sorry you didn't get a response sooner. I think test_contour.py would be a reasonable place to add a test.

@rcomer rcomer moved this from Needs review to Waiting for author in First Time Contributors Mar 3, 2025
AdamOrmondroyd
AdamOrmondroyd commented Mar 16, 2025
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@tacaswell tacaswell added this to the v3.11.0 milestone Mar 17, 2025
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I agree on both apologizing that this did not get attention earlier and adding a baseline image.

It is a surprising oversight that this has been missing!

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Seems to work (screenshot of contour_rasterization.pdf with dpi set to 25dpi)

Screenshot 2025-03-17 at 10 10 16

What tolerance is appropriate for image_comparison?

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rcomer commented Mar 17, 2025

Usually leaving the tolerance to default is fine. Sometimes it needs to be a little higher to accommodate slightly different results on different platforms. So you can just wait to see if CI passes.

jklymak
jklymak approved these changes Mar 17, 2025
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Looks good thanks!

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do I need access? I don't have a merge button

@rcomer rcomer merged commit 73d28ee into matplotlib:main Mar 18, 2025
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rcomer commented Mar 18, 2025

do I need access? I don't have a merge button

No, we just require two approving reviews before merging code changes.

Thanks for your work on this @AdamOrmondroyd and congratulations on your first Matplotlib PR! We hope to hear from you again.

@QuLogic QuLogic moved this from Waiting for author to Merged in First Time Contributors Mar 18, 2025
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@jklymak jklymak jklymak approved these changes

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topic: contour
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Status: Merged
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[Doc]: documentation of how to properly rasterize output of contourf
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@AdamOrmondroyd @tacaswell @rcomer @jklymak