[shiandow]

If there's one thing I've learned from image processing it's that the idea of a pixel as a perfect square is somewhat overrated.

Anti-aliasing is exactly as it sounds, a low-pass filter to prevent artefacts. Convolution with a square pulse is serviceable, but is not actually that good a low-pass filter, you get all kinds of moire effects. This is why a Bicubic kernel that kind of mimics a perfect low-pass filter (which would be a sinc kernel), can perform better.

It is tempting to use a square kernel though, because it's pretty much the sharpest possible method of acceptable quality.