Check this: How to maximize a plt.show() window using Python
The command is different depending on which backend you use. I find that this is the best way to make sure the saved pictures have the same scaling as what I view on my screen.
Since I use Canopy with the QT backend:
pylab.get_current_fig_manager().window.showMaximized()
I then call savefig() as required with an increased DPI per silvado's answer.