It seems like it's for only 2x, 3x and 4x. However with 3x and then downsampling using 2x bilinear filter it's possible to get 1.5.
It will look like (effective 1.5x):
Compare it to the:
http://www.hiend3d.com/hq3x.html
For me there is still a distortion visible...
It's not surprising as the...