For me, the imsave option origin="lower" is silently ignored when saving to PNG.

If I execute this script, the resulting two images are identical:

import numpy as np
from matplotlib.image import imsave

image = np.arange(30*20).reshape((20, 30))
imsave('lower.png', image, origin='lower')
imsave('upper.png', image, origin='upper')

Is this a MPL bug?

Version info: Python 3.5 as well as Numpy and MPL installed via macports, then MPL 2.0.0rc2 via pip in user site-packages, i.e. this is with MPL 2.0.0rc2.

lower.png is here:

upper.png is here: