plt.imshow(PIL.Image.open("lib/matplotlib/tests/baseline_images/test_image/uint16.tif"))

fails with

<elided>
  File "/home/antony/src/extern/matplotlib/lib/matplotlib/image.py", line 838, in make_image
    unsampled=unsampled)
  File "/home/antony/src/extern/matplotlib/lib/matplotlib/image.py", line 447, in _make_image
    if A.mask.shape == A.shape:
AttributeError: 'numpy.ndarray' object has no attribute 'mask'

since 12c27f3 (mpl 2.1 @tacaswell); previously it was possible to directly plot PIL-opened images (which do follow the standard buffer protocol).

It is not particularly problematic because one can just wrap explicitly the PIL-opened image using np.asarray, or use plt.imread instead (which does exactly that); still, I'm raising the issue here in case we want to fix it. (Or documenting that we no longer support PIL images is fine too, again the workaround is not that bad.)