ATI CrossFire Technology White Paper

esolution. This method has two main disadvantages. First, it requires rendering many more pixels than
normal, which can have a drastic impact on performance. Second, it results in an ordered grid sample pattern,
which does a poor job of anti-aliasing some types of jagged edges (specifically those that are nearly vertical or
nearly horizontal, which tend to result in the most noticeable problems).
Super AA overcomes both of these problems. It takes advantage of the second GPU to render the additional
pixels required for each frame, so there is little or no performance impact. Also, it can make use of a more
effective sample pattern (known as a rotated grid) that does a better job of anti-aliasing near-horizontal and
near-vertical edges, resulting in better overall image quality.
Two of the new Super AA modes use a combination of MSAA and SSAA to achieve the ultimate in image
quality. They work by not only using different sample multi-sample locations on each GPU, but by also
offsetting the pixel centers slightly as well. In effect, each GPU renders the image from a different viewpoint,
about half a pixel width apart. The new 10x and 14x Super AA modes operate in this way, combining 2x SSAA
with 4x and 6x MSAA respectively.
6x 6x AA AA
14x
14x
SuperAA
SuperAA
Comparison of SmoothVision HD 6x Anti-Aliasing (left) and new 14x Super AA mode (right).
Note how the branches and leaves look smoother and less pixelated in the image on the right.
Images taken from Half-Life 2 by Valve Software.
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