Bug report

Bug summary

When saving a 2d array in JPEG format, imsave generates an image of wrong dimension. This only happens for some specific array sizes, and only in JPEG (PNG outputs are fine for instance)

Code for reproduction

import matplotlib.image as mimg
import numpy as np
import PIL

x = np.zeros((1856, 1728))
mimg.imsave('foo.jpg', x, format='jpg')
jpg_im = PIL.Image.open('foo.jpg')
jpg_im.size

Actual outcome

(1728, 1855)

Expected outcome

(1728, 1856)

Matplotlib version

• Operating system: Debian 9
• Matplotlib version: 3.0.2
• Matplotlib backend (print(matplotlib.get_backend())): TkAgg
• Python version: 3.5.3
• Other libraries: PIL 5.0.0

matplotlib installed from pip