Antialiasing doesn't appear to work for png output (2.12)

[durack1]

Using the code example in #266 I have been trying to generate clean *.png output, however it seems that antialiasing is not working for this output format.

Example output seems to show slightly different file sizes, but the line output in the examples doesn't appear to improve with a high antialiasing setting - there are jaggies in all of the png outputs, whereas the pdf output is much sharper.

antialiasing = 1 (44.7K)

antialiasing = 8 (45.5K)

antialiasing = 64 (45.5K)

pdf output 171102_antiAliasing_1_.pdf