The Various D3D FSAA Modes

NVIDIA offers various FSAA quality settings under both D3D and OpenGL in the beta 5.22 drivers. We'll concentrate on the D3D modes, since the OpenGL modes are a subset of the D3D modes and the D3D modes are more complex. As suggested in the previous section, there are two parameters that can be adjusted to modify the quality (and hence performance) of anti-aliasing. The "over-sample" rate (increase in sub-samples) and the type of down-sample filtering can each be altered. NVIDIA uses these two parameters to create various settings, each with different speed/quality attributes.

In the case of the 5.22 beta drivers, the over-sample rates used are 2, 3, and 4. Thus, the screen resolution is increased in the horizontal and the vertical dimension by this factor. This means that these modes use 4 samples (2-by-2), 9 samples (3-by-3) and 16 samples (4-by-4). NVIDIA has also added a high-speed, low-quality, one dimensional over-sample mode where you use 2 samples in a 1-by-2 layout which essentially means you only get over-sampling in the vertical direction. This means that no anti-aliasing is achieved in one direction, or more specifically, vertical and near-vertical lines will still show aliasing effects. Basically this parameter gives us 4 different quality/speed modes.

For most of the FSAA modes, a normal 2-by-2 averaging filter is used to do the down-sampling, but NVIDIA also decided to include a special 3-by-3 filter which is used with 4 sub-samples. This setting should create slightly better results in terms of anti-aliasing, but may increase the overall blurriness of the final screen image.

An additional parameter that can influence the final image quality is the type of MIP-Map selected. MIP-Maps and MIP-Map levels are explained in our Voodoo5 5500 Image Quality article. MIP-Map levels determine the sharpness of textures by matching the onscreen resolution with the texture resolution. Simply said, there is a logical relation between the screen resolution and the resolution of the texture you use to render. As was explained in the first section, an important step in NVIDIA's anti-aliasing process is up-sampling to a higher resolution. When you up-sample to a higher resolution, the ideal MIP-Map level also changes. Using a higher resolution means that you should use a more detailed texture level for the best image quality. Recognizing this, NVIDIA permits you to choose either "High Detail MIP Level" or "Low Detail MIP Level" in each of the 4, 9, and 16 sample modes. "Low Detail MIP Level" will be faster, due to the more effective use of the on-chip texture cache. However, it also will produce more blurry graphics. Below, you can see an overview of the various FSAA modes that are available in NVIDIA's 5.22 beta drivers. They can be selected using the drivers' slider bar. From left to right, they are:

1. A 2-sample FSAA method with over-sampling only in the vertical direction while using a high Mip Level Selection. This mode should be very fast (due to the fact that only 2 samples are used) but the FSAA quality should be relatively poor since you only get anti-aliasing for near-horizontal edges. Near-vertical edges will not show any anti-aliasing. This mode is, in our personal opinion, inferior to the 3dfx 2-sample mode. 3dfx uses a Rotated Sampling Grid which results in anti-aliasing for both near-horizontal and near-vertical edges. These types of edges are particularly sensitive to aliasing artifacts.

2. A 4 sample FSAA method, with two-sample over-sampling in both the horizontal and vertical direction, but with Low Detail Mip Level. This will be the better than average speed setting, but with slightly blurry graphics due to the Mip Level Selection.

3. A 4-sample FSAA method, again [using two-sample over-sampling in both the horizontal and vertical direction, but with a High Detail Mip Level Selection. This will most likely be the optimal mode, offering good image quality and acceptable speed in most games. We expect this to be closer to 3dfx's 4X RGSS, but with less quality in the near-horizontal and near-vertical edges.

4. A 4-sample FSAA method, again using two-sample over-sampling in both the horizontal and vertical direction, with a High Detail Mip Level Selection AND with a 3 by 3 down sampling filter. This mode will offer slightly lower performance than mode 3 due to the extra bandwidth needed by the 3 by 3 filter (versus the 2 by 2 filter used in all of the other modes). The Anti-aliasing quality of this setting will appear visually higher than mode 3, but the overall blurriness might be increased a bit. This likely will vary with the application and the viewer.

5. A 9-sample FSAA method, using three-sample over-sampling in both the horizontal and vertical direction, with a Low Detail Mip Level Selection. This method will have high quality but limited speed and usability due to massive memory use.

6. A 9-sample FSAA method, again using three-sample over-sampling in both the horizontal and vertical direction, with a High Detail Mip Level Selection. This will provide higher quality due to sharper textures, but limited speed and usability due to massive memory use.

7. A 16-sample FSAA method, using four-sample over-sampling in both the horizontal and vertical direction, with a Low Detail Mip Level Selection. Very High Quality, but very limited speed and very low usability due to massive memory use (only 640x480x16bits supports this mode - see further).

8. A 16-sample FSAA method, again using four-sample over-sampling in both the horizontal and vertical direction, with a High Detail Mip Level Selection. This is the highest quality available from NVIDIA, but has very limited speed and very low usability due to massive memory use (only 640x480x16bits supports this mode - see further).

This overview should give you an idea of the various settings, their relative quality and speed.