Super Anti-Aliasing Mode - ATI Technologies X1900 - Radeon XTX 512 MB PCIE Video Card User Manual

CrossFire™ Rendering Modes 109
The main limitation of this mode is that it cannot be used in applications
where the appearance of the current frame is dependent upon data
generated in previous frames, since AFR generates successive frames
simultaneously on different GPUs. In these cases, the SuperTiling or
Scissor Mode is used instead.

Super Anti-aliasing Mode

Anti-aliasing (AA) is a rendering technique designed to remove jagged
edges, shimmering, and pixelation problems that are common in rendered
3D images. Rather than simply determining the color of each pixel on the
screen by sampling a single location at the pixel's center, anti-aliasing
works by sampling multiple locations within each pixel and blending the
results together to determine the final color.
The latest generation of ATI's Radeon® GPUs with SmoothVision™ HD
technology uses a method known as Multi-sample Anti-aliasing (MSAA).
This method takes samples from 2, 4, or 6 programmable locations within
each pixel, and uses gamma correct sample blending for high-quality
smoothing of polygon edges. The new CrossFire Super Anti-aliasing mode
takes advantage of the programmable sample capability of
SmoothVision™ HD to provide higher quality anti-aliasing on CrossFire™
systems.
It works by having each GPU render the same frame with anti-aliasing
enabled, but uses different sample locations for each. When both versions
of the frame are completed, they are blended in the CrossFire Compositing
engine. The resulting image has effectively twice the number of samples,
so 4x and 6x Anti-aliasing becomes 8x and 12x Super Anti-aliasing,
respectively.