Xh3maa
I had the same problem in the past, for a long time I couldn't find the solution, over 4 months researching and testing and error until I found one way that works for me at the moments.
once you draw your art use this script for Illustrator to save the PNG:
http://www.ericson.net/content/2011/10/illustrator-multiexporter-jpg-and-eps/
Like they recommended the colleagues above size the art on Illustrator to the size you gonna use on C2
on the exporting time: scale the art, they will give you one option there before you export it with the script, the best results I got was with 150% scale
or just keep playing with the scale until you find a good and clear PNG
I hope it helps