Bug report

Bug summary

imshow (and friends, e.g., pcolormesh) don't tightly fit the image inside the axes. I suspect an off-by-one error somewhere (see the hint section at the bottom).

Code for reproduction

from matplotlib import pyplot as plt

fig = plt.figure(figsize=(3.423,2.92917))
ax = plt.Axes(fig, [0.2,0.2,0.2,0.2])
fig.add_axes(ax)

ax.imshow([[1,2],[3,4]],rasterized=True)
plt.savefig('gap.pdf')

Actual outcome

gap.pdf

Expected outcome

There should be no gap between the x axis, and the image.

Matplotlib version

• Operating system: linux
• Matplotlib version: 3.2.2 (but also later 3.4.0)
• Python version: 3.8

Hints

I don't have time to dig into this right now, but it is corrected (for my particular figure size) by subtracting 1 from the y parameter in the draw_image call in the stop_rasterizing definition of backend_mixed.py. I.e., change

self._renderer.draw_image(
    gc,
    l * self._figdpi / self.dpi,
    (height-b-h) * self._figdpi / self.dpi,
    image)

to

self._renderer.draw_image(
    gc,
    l * self._figdpi / self.dpi,
    (height-b-h) * self._figdpi / self.dpi - 1,
    image)

Hopefully that might help someone track this down.