Anti-aliasing (AA) is a computer graphics technique that attempts to minimise the unwanted 'staircase' or jagged object outlines which occur due to the limited resolution in 3D-Renderers, essentially by 'smoothing' these lines. Enabling this graphics feature will also increase the texture quality in some cases.
 Example of Anti-Aliasing
|No anti-aliasing||16x anti-aliasing|
 Types of Anti-Aliasing
There are a number of anti-aliasing techniques today but all of them are based on the same principle. They simply render multiple pixels per pixel of the final image.
The techniques only differ on two factors:
- How they determine which pixels are aliased.
- How they "mix" the multiple rendered pixels to get the final pixel.
These algorithms are also variable on how many pixels they use to determine one final pixel. In video games this is represent by a simple number which is a power of 2 like 2x, 4x, 8x etcetera.
There are several terms associated with anti-aliasing, most of which are derivatives on the standard anti-aliasing formula:
- Coverage Sampling Antialiasing (CSAA): This is an nVidia-developed form of anti-aliasing which was first released for the GeForce 8-series of graphics cards. It aims to further reduce the additional stress that MSAA puts on the system, with nVidia claiming that a CSAA-rendered image will rival 8x-16x MSAA whilst only putting a load on the system comparable to 4x MSAA. It does this by reducing the number of settings each sample determines (by creating a new sample for coverage) whilst increasing the overall number of samples.
- Fast Approximate Anti-Aliasing (FXAA): This is nVidias version of post-processing anti-aliasing, applied after the image is rendered unlike more traditional anti-aliasing methods such as MSAA and SSAA/FSAA. This means that many titles which are DirectX 9 and later and which did not previously support anti-aliasing will be able to utilise FXAA; simply because it is applied post-process. However, the image quality improvement it provides is significantly less impressive than traditional AA methods such as MSAA.
- Morphological Anti-Aliasing (MLAA): Developed by Intel  (First used by Sony in some PS3 games and later implemented in AMD's GPU driver), this anti-aliasing technique is a form of post-processing anti-aliasing, applied after the image is rendered unlike more traditional anti-aliasing methods such as MSAA and SSAA/FSAA. AMD claim it outperforms FXAA at comparable settings. SMAA is an upgraded form of it.
- Subpixel Morphological Anti-Aliasing (SMAA): A post-process AA from Crytek, it gives a very edge-free image at a cost of image sharpness. Implementations vary from game to game, so image quality varies, but it's arguably better than FXAA or MLAA. You can find pictures, videos and a demo from the developer's site.
- Multisample Anti-Aliasing (MSAA): This type of anti-aliasing is essentially a 'budget' version of supersampling. To reduce the stress that SSAA/FSAA puts on a system, Multisampling optimises the process by evaluating each pixel only once, with true supersampling only occurring at the edges of a rendered object, and to depth values. This results in a similar (but less drastic) improvement in visual quality whilst reducing the load put on the system to render and downscale such high resolutions.
- Quincunx Super Anti-Aliasing (QSAA): This type of anti-aliasing was also introduced by nVidia and improves on standard MSAA somewhat. For example, 2x QSAA roughly equates to 3x MSAA in terms of quality.
- Supersampling (SSAA): Also known as Fullscreen Anti-Aliasing (FSAA), this option applies the general anti-aliasing formula to fullscreen images, reducing the 'staircase effect' mentioned above. This type of anti-aliasing has largely been replaced by MSAA however, due to the huge stress SSAA/FSAA puts on the GPU. When compared to a rendered image undergoing MSAA, a SSAA/FSAA image will appear smoother and most likely more realistic. Due to the better result that FSAA provides, some games still adopt it as an option in the in-game settings.
Essentially there are two main groups of anti-aliasing - those applied during rendering and those applied post-rendering, or post-processing. The former offer much better graphical improvements at the cost of a heavy load on the graphics card. The latter, which include MLAA, FXAA and SMAA, are intended to demand much less from the graphics card but consequently offer a much less noticeable improvement to graphics.
 Impact on Graphical Quality
Anti-aliasing improves the general graphics quality but lowers the frame rate quite significantly. Lowering or disabling the anti-aliasing effect is a good way to improve the overall frame-rate. An anti-aliasing setting is present in most PC games. If its not available in a specific title, it is usually possible to force it via the graphics card driver or a mod/hack. For ATI cards, anti-aliasing can be forced via the Catalyst Control Centre (CCC), and for nVidia cards it can be forced via the Control Panel.
For lower-end systems, prioritise post-process anti-aliasing types such as FXAA and MLAA, as these will result in a much lower reduction in frame rates. If your system is up to it, however, use more traditional anti-aliasing methods such as MSAA to drastically improve overall image quality.
- ↑ http://www.codinghorror.com/blog/2011/12/fast-approximate-anti-aliasing-fxaa.html
- ↑ http://visual-computing.intel-research.net/publications/papers/2009/mlaa/mlaa.pdf
- ↑ http://en.wikipedia.org/wiki/Multisample_anti-aliasing
- ↑ http://www.overclock.net/t/206755/msaa-and-qsaa
- ↑ http://en.wikipedia.org/wiki/Anti-aliasing#Super_sampling_.2F_full-scene_anti-aliasing