Graduation Project: Anti-Aliasing Filter for Regular Shadow Maps

During my specialization at NHTV it came to my attention that filtering techniques (such as Variance Shadow MapsPercentage Closer Filtering) produce a relatively good visual result, with a low implementation complexity and GPU load in contrast to sample redistribution techniques.

Near the end of my specialization, an idea was forming of attempting to use already existing anti-aliasing filtering techniques (such as MLAA, SMAAFXAA, etc) to improve the visual quality of a regular shadow mapping technique (Lance Williams 1978). However the implementation complexity will be relatively high and the GPU load will be higher than regular filtering techniques.

By using a regular screen-spaced AA-Filter, the shadow map quality exerts minor improvement, but insufficient to remove perspective aliasing. Later on I’ve found an interseting document on shadow maps in combination with FXAA. The shadow blockiness (shadow silhouette perspective aliasing) has been significantly reduced, however the the perspective aliasing is still very visible.

Regular anti-aliasing filter is based on a flat-projection, which also takes insufficient parameterization into account to reduce shadow map perspective aliasing. By transforming the 2D screen-plane back into the light-space projection (the space where the original shadow map is being rasterized) and taking the original shadow map parameterization into account, the AA-Filter can be then a more specialized technique to improve visual quality of a regular shadow map.

In following weeks I am going to:

  1. Research existing 2D post-processing anti-aliasing techniques.
  2. Determine the most suitable candidate technique for the implementation.
  3. Develop AA Filter for shadow maps based on implemented aa-filter with space transformation and shadow map parameterization.

If the technique is successful, a further research can be done in certain areas:

  1. Combination with sample redistribution techniques (Cascaded Shadow MapsLight Space Perspective Shadow Maps).
  2. Research exotic AA-Filtering techniques such as NSAA and TXAA.

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