Quick aside for Jaqui:

That's how your eyes work to compensate for differences in depth of field. If you look at a straight edged object - such as a the side of a chair - against a highly contrasting background, you'll see that at the edges there's a little blur. Anti aliasing reproduces this effect.

It also compensates for the corners of the square pixels we work with - sort of smoothing them out so they don't have a zig zag appearance against whatever is behind them.

Anti aliasing definately adds to render time but it also adds to the realism of the render.

Sometimes it can be bypassed by rendering the image at a much larger size (at least 2x) and then reducing the image size in a photo-retouching software. When you scale down an image, the software averages out the pixels; the same thing happens as with anti aliasing:

"it dithers the colour of the pixel by what is in the surounding pixels...it actually blurrs the edges of the objects in the image.
if left side pixel is white and right side is green, then the pixel in question becomes light green."

The quality varies depending on the image - quality being defined as the ability to create realistic edges.

Before they made me they broke the mold!
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