2xQ is the former Quincunx AA.
The performance of 2x AA & 2xQ AA is almost identity,
however,Quincunx / 2xQ AA would bur the whole image.
You may see the difference between them in my previous article:
http://202.39.48.38/showthread.php?threadid=243546

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sorry,i couldnt type chinese while i am in the lab.....