Why different figure size for screen/savefig even dpi is the same?


This, http://imgur.com/a/q9UvR contains two pictures.

One is drawn by the plt.show(), the other is by plt.savefig and then
opened by the pdf reader.

All the settings are the same, including the dpi. ( I am using matplotlib2)

Why does the figure size differ ?

The one shown in the pdf reader seems normal, however, the one in the
default plt.show() is a little bit small.

I am on macos with retina, if that makes a difference.