Pip install Matplotlib error with virtualenv

To generate graph in png format you need to Install following dependent packages

sudo apt-get install libpng-dev
sudo apt-get install libfreetype6-dev

Ubuntu https://apps.ubuntu.com/cat/applications/libpng12-0/ or using following command

sudo apt-get install libpng12-0

As I have struggled with this issue twice (even after fresh kubuntu 15.04 install) and installing freetype did not solve anything, I investigated further.

The solution:
From github issue:

This bug only occurs if pkg-config is not installed;
a simple
sudo apt-get install pkg-config
will shore up the include paths for now.

After this installation proceeds smoothly.

Building Matplotlib requires libpng (and freetype, as well) which isn't a python library, so pip doesn't handle installing it (or freetype).

You'll need to install something along the lines of libpng-devel and freetype-devel (or whatever the equivalent is for your OS).

See the building requirements/instructions for matplotlib.