Transparency & Adaptive AA Explained

NVIDIA - Transparency Anti-Aliasing:

The differences between 4xAA with transparency multisampling and a conventional 4xAA don't appear to be quite as large as the performance differences between ATI's performance adaptive AA and the company's conventional 4xAA. However, the performance differences between transparency multisampling and conventional anti-aliasing are small in all cases that we've examined here. Also, it's worth noting that the screen shots don't appear to do the method as much justice as they probably should.

Transparency multisampled anti-aliasing appears to concentrate on sampling scenery that is closer to the player, meaning that the image quality is good in the player's vicinity, but it tails off as the scenery gets further away from the player. It almost seems like distant foliage isn't being sampled at all.

That's not strictly the case though, and it's just the nature of multisampled anti-aliasing in general - as the textures get smaller, taking accurate colour samples is harder to do. This in turn means that a multisampled scene will never look as good as one that is supersampled. However, where performance is a concern, transparency multisampling is an acceptable trade off in image quality.

Transparency supersampling really smooths out the entire scene in much the same way that quality adaptive anti-aliasing does. The static image quality is visibly better than what can be achieved with either transparency multisampling or conventional anti-aliasing, and the quality improvements become even more apparent when you start moving through areas where large amounts of alpha-tested textures are used to represent high detail scenes where geometry and opaque textures are unrealistic from a performance perspective.

The large amount of alpha-tested textures used in the chain link fences help to highlight the differences between the transparency multisampling and transparency supersampling techniques used by NVIDIA on its GeForce 7-series GPUs. Again, there are some very subtle differences between the conventional 4xAA and transparency multisampling mode in static screen shots. The performance differences between 4xAA and 4xTMS AA are again very small. That is a good thing because the subtle image quality differences between the two are enhanced when the player is moving around.

When comparing transparency supersampling with transparency multisampling, the differences in performance and, more importantly, image quality are quite large. This is because there a lot of additional detail that is getting sampled by NVIDIA's transparency supersampled anti-aliasing alogithm. The resultant image quality output is almost exactly the same as the output deliverd by ATI's quality adaptive anti-aliasing technique.