Anti-Aliasing
From TPU Reference
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Overview
Anti-aliasing (commonly abbreviated AA) is a method used by low resolution devices, such as computer monitors, to make jagged edges appear smoother. Anti-aliasing is often used to display on-screen text and graphics, as well as in 3D gaming. Much of the processing burden traditionally associated with AA has been shifted from the CPU to the GPU, greatly increasing its adoption, especially with modern games.
Three dimensional approaches
Full Scene Anti-Aliasing
The most basic form of 3D anti-aliasing, Full Scene Anti-Aliasing (FSAA) renders a scene at twice the resolution, then downsampled to produce the anti-aliased image. Usually higher quality images can be attained by increasing the upsample rate. This form of AA is the most computationally expensive.
Supersampling
Supersampling works by taking the value of several pixels in an area and then producing an average, which is displayed. As with any other anti-aliasing technique, more accurate representations can be obtained by increasing the sampling rate, which normally ranges from 2x to 16x.
Multisample Anti-Aliasing
Introduced by NVIDIA in 2001, MSAA relies on multiple subpixel samples (and hence the name) to smooth out textures. At high resolutions, or with an increasing number of samples, the load placed by MSAA requires a powerful graphics card to output acceptable framerates. A number of technologies such as transparency and gamma-corrected anti-aliasing have since been released to streamline this process and increase image quality.
Coverage Sample Anti-Aliasing
Coverage Sample Anti-Aliasing (CSAA), introduced with the GeForce 8 Series GPUs, allows for anti-aliasing quality similar to that of 16xMSAA at nearly the same speed as 4xMSAA. It differs from previous techniques in that it samples only coverage instead of, say, shaded colors, stored colors, and stencil. Doing so allows for high-quality graphics without the overhead usually associated with anti-aliasing.
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