FIX: ensure images are C order before passing to pillow

closes matplotlib#28020

Author: tacaswell

lib/matplotlib/image.py

@@ -1640,6 +1640,7 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
             # we modify this below, so make a copy (don't modify caller's dict)
             pil_kwargs = pil_kwargs.copy()
         pil_shape = (rgba.shape[1], rgba.shape[0])
+        rgba = np.require(rgba, requirements='C')
         image = PIL.Image.frombuffer(
             "RGBA", pil_shape, rgba, "raw", "RGBA", 0, 1)
         if format == "png":

lib/matplotlib/tests/test_image.py

@@ -205,6 +205,14 @@ def test_imsave(fmt):
     assert_array_equal(arr_dpi1, arr_dpi100)
 
 
+@pytest.mark.parametrize("origin", ["upper", "lower"])
+def test_imsave_rgba_origin(origin):
+    # test that imsave always passes c-contiguous arrays down to pillow
+    buf = io.BytesIO()
+    result = np.zeros((10, 10, 4), dtype='uint8')
+    mimage.imsave(buf, arr=result, format="png", origin=origin)
+
+
 @pytest.mark.parametrize("fmt", ["png", "pdf", "ps", "eps", "svg"])
 def test_imsave_fspath(fmt):
     plt.imsave(Path(os.devnull), np.array([[0, 1]]), format=fmt)