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BUG: Fix _extent not set in PcolorImage #9442

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Merged
merged 1 commit into from
Oct 23, 2017
Merged

BUG: Fix _extent not set in PcolorImage #9442

merged 1 commit into from
Oct 23, 2017

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AtharvaKhare
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@AtharvaKhare AtharvaKhare commented Oct 16, 2017 •
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PcolorImage now sets _extent of AxesImage on its creation.

PR Summary

Depending on bins argument of hist2d, style is set to either image or pcolorimage in _axes.pcolorfast. If the style is image, AxesImage object is created and is supplied with extents. The issue arose when style was pcolorimage. The _extent is never set in super class AxesImage of PcolorImage.
The issue is solved by setting _extent after PcolorImage creation.

This PR fixes #8426.

PR Checklist

  • Has Pytest style unit tests
  • Code is PEP 8 compliant
  • New features are documented, with examples if plot related
  • Documentation is sphinx and numpydoc compliant
  • Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
  • Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way

@jklymak
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jklymak commented Oct 18, 2017

Thanks for this! Can you supply a test that doesn't work w/ master but does work with your suggested change? It'd help (me?) to get context for it.

@AtharvaKhare
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@jklymak Sample example from issue:

import pylab as plt
x = plt.hist2d([1,2,3], [3,5,6], bins=[[0,3,7], [1,2,3]])
im = x[-1]
print(type(im))
print(im.get_window_extent())

The issue arose when plt.hist2d returns object of matplotlib.image.PcolorImage.
hist2d returns either matplotlib.image.AxesImage or matplotlib.image.PcolorImage depending on the parameter bins. The condition for selection is:

matplotlib/lib/matplotlib/axes/_axes.py

Lines 5781 to 5795 in d7ddd47

elif len(args) == 3:
x, y = args[:2]
x = np.asarray(x)
y = np.asarray(y)
if x.ndim == 1 and y.ndim == 1:
if x.size == 2 and y.size == 2:
style = "image"
else:
dx = np.diff(x)
dy = np.diff(y)
if (np.ptp(dx) < 0.01 * np.abs(dx.mean()) and
np.ptp(dy) < 0.01 * np.abs(dy.mean())):
style = "image"
else:
style = "pcolorimage"

Followed by creation of object:

matplotlib/lib/matplotlib/axes/_axes.py

Lines 5837 to 5842 in d7ddd47

if style == "image":
im = mimage.AxesImage(self, cmap, norm,
interpolation='nearest',
origin='lower',
extent=(xl, xr, yb, yt),
**kwargs)

or

matplotlib/lib/matplotlib/axes/_axes.py

Lines 5845 to 5850 in d7ddd47

elif style == "pcolorimage":
im = mimage.PcolorImage(self, x, y, C,
cmap=cmap,
norm=norm,
alpha=alpha,
**kwargs)

Here extent was not specified while creation of the PcolorImage object.

matplotlib/lib/matplotlib/image.py

Line 980 in d7ddd47

super(PcolorImage, self).__init__(ax, norm=norm, cmap=cmap)

PcolorImage calls AxesImage constructor with extent=None, which causes error when referenced.

In short, to recreate error, create any PcolorImage object and reference its parent's(AxesImage) extents. To do this, elements of bins must be of dim 1 and size >=3, with intervals such that the do not satisfy:

matplotlib/lib/matplotlib/axes/_axes.py

Lines 5789 to 5795 in d7ddd47

dx = np.diff(x)
dy = np.diff(y)
if (np.ptp(dx) < 0.01 * np.abs(dx.mean()) and
np.ptp(dy) < 0.01 * np.abs(dy.mean())):
style = "image"
else:
style = "pcolorimage"

Basically some non-equally spaced bins.

@dstansby
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Could you add the test in lib/matplotlib/tests/test_image.py? It doesn't need to be an image test, but just a test to check that the code doesn't fail.

@AtharvaKhare
BUG: Fix _extent not set in PcolorImage
ee3d090 
Fixes #8426. Added test to check `extent`:
`lib/matplotlib/tests/test_image.py::test_pcolorimage_extent()`
@AtharvaKhare
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Changed the way _extent is set.

@dstansby Added test.

@tacaswell tacaswell added this to the v2.1.1 milestone Oct 23, 2017
@tacaswell tacaswell merged commit 5a4cf14 into matplotlib:master Oct 23, 2017
lumberbot-app bot pushed a commit that referenced this pull request Oct 23, 2017
@tacaswell
Backport PR #9442: BUG: Fix _extent not set in PcolorImage
7dd34d7
@lumberbot-app lumberbot-app bot mentioned this pull request Oct 23, 2017
Merged
NelleV added a commit that referenced this pull request Oct 23, 2017
@NelleV
Merge pull request #9542 from matplotlib/auto-backport-of-pr-9442
b206b0c 
Backport PR #9442 on branch v2.1.x
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PcolorImage does not set _extent
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@AtharvaKhare @jklymak @dstansby @tacaswell