matplotlib savefig in jpeg format

Question

I am using matplotlib (within pylab) to display figures. And I want to save them in .jpg format. When I simply use the savefig command with jpg extension this returns :

ValueError: Format "jpg" is not supported.

Supported formats: emf, eps, pdf, png, ps, raw, rgba, svg, svgz.

Is there a way to perform this ?

Answer 1

You can save an image as 'png' and use the python imaging library (PIL) to convert this file to 'jpg':

import Image
import matplotlib.pyplot as plt

plt.plot(range(10))
plt.savefig('testplot.png')
Image.open('testplot.png').save('testplot.jpg','JPEG')

The original:

The JPEG image:

Answer 2

To clarify and update @neo useful answer and the original question. A clean solution consists of installing Pillow, which is an updated version of the Python Imaging Library (PIL). This is done using

pip install pillow

Once Pillow is installed, the standard Matplotlib commands

import matplotlib.pyplot as plt

plt.plot([1, 2])
plt.savefig('image.jpg')

will save the figure into a JPEG file and will not generate a ValueError any more.

Contrary to @amillerrhodes answer, as of Matplotlib 2.0, JPEG files do not seem to be supported. If I remove the Pillow package I still receive a ValueError about an unsupported file type.

Answer 3

Just install pillow with pip install pillow and it will work.

Answer 4

I just updated matplotlib to 1.1.0 on my system and it now allows me to save to jpg with savefig.

To upgrade to matplotlib 1.1.0 with pip, use this command:

pip install -U 'http://sourceforge.net/projects/matplotlib/files/matplotlib/matplotlib-1.1.0/matplotlib-1.1.0.tar.gz/download'

EDIT (to respond to comment):

pylab is simply an aggregation of the matplotlib.pyplot and numpy namespaces (as well as a few others) jinto a single namespace.

On my system, pylab is just this:

from matplotlib.pylab import *
import matplotlib.pylab
__doc__ = matplotlib.pylab.__doc__

You can see that pylab is just another namespace in your matplotlib installation. Therefore, it doesn't matter whether or not you import it with pylab or with matplotlib.pyplot.

If you are still running into problem, then I'm guessing the macosx backend doesn't support saving plots to jpg. You could try using a different backend. See here for more information.

Answer 5

Matplotlib can handle directly and transparently jpg if you have installed PIL. You don't need to call it, it will do it by itself. If Python cannot find PIL, it will raise an error.