Gaussian anti-aliasing is a improves image quality by randomly sampling the geometry within a pixel rather than sampling the geometry at the pixel center. The idea is brought over from ray-tracing where the color of a pixel is determined by randomly sampling geometry within each pixel. It achieves perceptual smoothing of rendered images with zero impact to rendering performance.
Under traditional rasterization procedures, the color of a pixel is determined by checking whether a triangle overlaps the pixel at its exact center. This leads to a grating pattern commonly known as jaggies. Instead of sampling geometry at exact pixel centers, Gaussian anti-aliasing samples a random point within each pixel. As this occurs repeatedly as in the case with realtime renderered content, the perceived color of the pixel converges towards a more accurate depiction of the geometry that lies within that pixel.
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Due to persistence of vision — the effect that causes us to see motion in a sequence of animated frames — successive frames appear blended. With high frequency displays and realtime rendered content, the user just sees a smooth image free of jaggies. Whereas temporal anti-aliasing adds additional processing steps by jittering and blending a sequence of frames, Gaussian anti-aliasing achieves a smoother image with zero impact to performance.
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