[Bug]: figimage producing inconsistent results

[swfiua]

Bug summary

figimage() is producing inconsistent results.

It appears a transform is sometimes applied to the image and sometimes not.

Code for reproduction

from matplotlib import pyplot
plt = pyplot
import numpy as np

fig = pyplot.figure()
ax = fig.subplots()


fig_bbox = fig.bbox
width, height = fig_bbox.width, fig_bbox.height

img = np.zeros((int(height), int(width), 3))
img += (127, 0, 0)

fig.figimage(img, 0, 0, zorder=-1)

# show the figure, image is not scaled as I would expect
plt.show()

# save as a png, image is scaled as I would expect
fig.savefig('foo.png')

# save as an svg, image matches the one in the FigureCanvas window.
fig.savefig('foo.svg')

# NB reversing the order of the two savefig calls produces images
# matching the FigureCanvas version.

Actual outcome

Expected outcome

I would expect all images to look like the png image, i.e. scaled to the figure size.

Additional information

No response

Operating system

Ubuntu 21.10

Matplotlib Version

3.5.0.dev2201+ge9bd017b2d.d20220707

Matplotlib Backend

'QtAgg'

Python version

Python 3.9.7

Jupyter version

No response

Installation

git checkout

[jklymak]

The dpi changes during the lifetime of the figure, so its not surprising that the image changes size. Did you want the resize=True option? https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.figimage.html

[swfiua]

Thanks, I hadn't considered dpi changes.

Including resize=True in the call to figimage doesn't seem to change the behaviour.

I am looking for is a reliable way to put a patch of color on the figure -- in my actual code I am not looking for a patch that covers the whole figure, this is just toy code to demonstrate the issue.

[jklymak]

it wouldn't surprise me if figimage has fallen out of repair. I guess someone could fix it, but I'm not a particular fan of the API.

If you just want a patch, then just use Patch, and set the transform to fig.transFig. If you want a background image, I'd just make an axes that fills the whole figure (fig.add_axes([0, 0, 1, 1])).

[swfiua]

Thanks very much for this, most helpful.
I've gone with adding a background axes that fills the whole figure and it seems to be working nicely.
Inclined to agree re: figimage API, given the dpi issue.

[jklymak]

I think we can re-open. Either the action item is to deprecate figimage or to fix it so at least the resize option works.