FFAA

To enable the FFAA post-process shader you must first open the Shading panel by using either the Manager > Shading command or the Ctrl + 3 shortcut.

Once the Shading panel is opened, select the Rendering tab: the first column on the left displays the Rendering chain that lists, among others, the FFAA option. Check the radio button on to enable it and be allowed to modify parameters that are displayed in the column beside.

FFAA stands for Feature-Following Anti-Aliasing, a post-process shader, which anti-aliases pixel-connected features in an image by high-resolution sub-sampling, while propagating further anti-aliasing between pixels only where necessary. Speed is maximized automatically by super-sampling only on those areas requiring such anti-aliasing.

Default values are:

"threshold" 0.01

"relative sensitivity" 4.0

The "ffaa" shader provides faithful rendering of connected features extending over several pixels, super-sampling all such pixels efficiently and avoiding the super-sampling of any pixels outside such features. Samples are taken at the corners of a pixel; if this exhibits a difference exceeding a specified "threshold", then that pixel is considered to contain a high frequency feature and is super-sampled accordingly. The "ffaa" shader adaptively applies high frequency super-sampling to those pixels containing features requiring anti-aliasing, but will not expend time on those which do not.

The "relative sensitivity" parameter determines the threshold applied when deciding whether a pixel contains a feature or not. As each successive sample is taken, the cumulative standard deviation of the samples is calculated in a color space allowing for the relative sensitivity of the red, green and blue cones of the human eye. If this standard deviation a) ever exceeds the threshold value, the pixel is taken to contain features, b) never exceeds the threshold value, the pixel is taken not to contain any feature. The "relative sensitivity" parameter should be set high enough to ensure that all pixels containing features are detected (the higher the parameter, the more pixels are reached).

The "threshold" parameter should be low enough to ensure that all pixels that contain features are tagged as seeds but not so low that any pixel not containing any feature is incorrectly tagged as a seed.