For lines and ellipses in PIL, the images are rough.
I found antialiasing only in resize and thumbnail.
Is there any way to do antialiasing when drawing a line or ellipse?
The only way to do it natively is with supersampling. Render your image at a multiple of the size you require, then resize it with filter=Image.ANTIALIAS.
aggdraw (http://effbot.org/zone/aggdraw-index.htm) may be something you're interested in.
The aggdraw module implements the basic WCK 2D Drawing Interface on top of the AGG library. This library provides high-quality drawing, with anti-aliasing and alpha compositing, while being fully compatible with the WCK renderer.
The aggdraw module can be used with PIL or the WCK library (under Tkinter or native Windows). It can also be used as a stand-alone library.
来源：https://stackoverflow.com/questions/14350645/is-there-an-antialiasing-method-for-python-pil