Fast approximate anti-aliasing (FXAA) is a screen-space

anti-aliasing Anti-aliasing may refer to any of a number of techniques to combat the problems of aliasing in a sampled signal such as a digital image or digital audio recording. Specific topics in anti-aliasing include: * Anti-aliasing filter, a filter used be ...

algorithm created by Timothy Lottes at

Nvidia Nvidia CorporationOfficially written as NVIDIA and stylized in its logo as VIDIA with the lowercase "n" the same height as the uppercase "VIDIA"; formerly stylized as VIDIA with a large italicized lowercase "n" on products from the mid 1990s to ...

. FXAA 3 is released under a

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license. A later version, FXAA 3.11, is released under a 3-clause BSD license.

Algorithm description

# The input data is the rendered image and optionally the luminance data. # Acquire the luminance data. This data could be passed into the FXAA algorithm from the rendering step as an alpha channel embedded into the image to be antialiased, calculated from the rendered image, or approximated by using the green channel as the luminance data. # Find high contrast pixels by using a high pass filter that uses the luminance data. Low contrast pixels that are found are excluded from being further altered by FXAA. The high pass filter that excludes low contrast pixels can be tuned to balance speed and sensitivity. # Use contrast between adjacent pixels to heuristically find edges, and determine whether the edges are in the horizontal or vertical directions. The blend direction of a pixel will be perpendicular to the detected edge direction on that pixel. # Calculate one blend factor for a high-contrast pixel by analyzing the luminance data in the 3x3 grid of pixels with the pixel in question being the center pixel. # Search along the detected edge to determine how long that edge goes for and what direction the actual edge goes when the detected horizontal or vertical edge ends in order to take into account the actual edge's direction in order to calculate a second blend factor. This step can be tuned for more quality by increasing the search resolution and how far the search goes before the search for the edge's end gives up, or for more speed by reducing both. # Blend the pixel using the chosen blend direction and the maximum of both of the blend factors that were calculated.

Comparison

The main advantage of this technique over conventional spatial anti-aliasing is that it does not require large amounts of

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. It achieves this by smoothing undesirable jagged edges ("

jaggies "Jaggies" is the informal name for artifacts in raster images, most frequently from aliasing, which in turn is often caused by non-linear mixing effects producing high-frequency components, or missing or poor anti-aliasing filtering prior to samp ...

") as

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...

s, according to how they appear on-screen, rather than analyzing the

3D model In 3D computer graphics, 3D modeling is the process of developing a mathematical coordinate-based representation of any surface of an object (inanimate or living) in three dimensions via specialized software by manipulating edges, vertices, an ...

itself, as in conventional spatial anti-aliasing. Since it is not based on the actual

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, it will smooth not only edges between triangles, but also edges inside alpha-blended textures, or those resulting from

pixel shader In computer graphics, a shader is a computer program that calculates the appropriate levels of light, darkness, and color during the rendering of a 3D scene - a process known as ''shading''. Shaders have evolved to perform a variety of spec ...

effects, which are immune to the effects of

multisample anti-aliasing Multisample anti-aliasing (MSAA) is a type of spatial anti-aliasing, a technique used in computer graphics to remove jaggies. Definition The term generally refers to a special case of supersampling. Initial implementations of full-scene anti-al ...

(MSAA). The downsides are that high contrast

texture maps Texture mapping is a method for mapping a texture on a computer-generated graphic. Texture here can be high frequency detail, surface texture, or color. History The original technique was pioneered by Edwin Catmull in 1974. Texture mapping ...

are blurred, that FXAA must be applied ''before'' rendering the

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elements of a game lest it affect them too, and that polygonal details smaller than one pixel that would have been captured and rendered by MSAA and SSAA cannot be captured and rendered by FXAA alone.

References

{{reflist Anti-aliasing algorithms

Algorithm description

Comparison

See also

References