It assumes the image is uint8 and incorrectly wraps the input at 255:
In [1]: from skimage import io
In [15]: io.imsave('io3.png', np.array([[0, 1], [0, 4196]], dtype=np.uint16),
plugin='pil')
In [19]: from matplotlib.pyplot import imread
In [20]: imread('io3.png')
Out[20]:
array([[ 0. , 0.00392157],
[ 0. , 0.39215687]], dtype=float32)
In [21]: import matplotlib as mpl
In [22]: mpl.__version__
Out[22]: '1.3.1'
It assumes the image is uint8 and incorrectly wraps the input at 255: