View topic - Which antialiasing filter to use?

Which antialiasing filter to use?

General discussion on lighting, backgrounds, Global Illumination, rendering parameters and tonnemapping.

Which antialiasing filter to use?

Post Sun Mar 15, 2015 6:51 pm

Rendering an image can be considered as sampling a signal that varies over a 2D image plane. An anti-aliasing filter is used to restrict the bandwidth of the "signal" to approximately satisfy the sampling theorem:

http://en.wikipedia.org/wiki/Sampling_theorem

Roughly speaking, it filters out ray samples that does not fit in the continuity and smoothness of the final image. However, an anti-aliasing filter is also a trade-off, particularly in high contrast areas. Some filters reveal more detail but they also produce a worse aliasing on high contrast areas such as highlights on mirror components, visible area lights and in general fast high-contrast transitions. Besides, some post processing tools on HDR data will make things worse regarding high contrast aliasing.

This is particularly true for two filters whose functions have negative lobes, which are Mitchell-Netravali and Lanczos. Both are used to amplify diffuse detail, but they will produce worse aliasing on high contrast areas as well. Lanczos function negative lobe is bigger than Mitchell-Netravali therefore it will reveal more detail than Mitchell but it will also produce more aliasing on high contrast areas. The negative lobe means that Lanczos and Mitchell 'reverberates' over the edges of the image plane feaures (objetcs, shadows, hightlights, texturing) which brings detail up.


box.jpg
box.jpg (2.61 KiB) Viewed 3005 times

gauss.jpg
gauss.jpg (3.66 KiB) Viewed 3005 times

Mitchell.jpg
Mitchell.jpg (3.69 KiB) Viewed 3005 times

Lanczos.jpg
Lanczos.jpg (3.31 KiB) Viewed 3044 times


Which one to use ?
  • The faster one but with the poorer results is Box, so it is recommended for tests.
  • Gauss is the "perfect" filter when you can reveal detail by just using a very big imagen resultion and/or you want to keep your highlights aliasing in check, for instance when you are doing studio lighting of a car with arealights and lot of mirror component. Gauss also helps a bit to blur the montecarlo noise and it is also less prone to moire patterns.
  • Mitchel and Lanczos are good to amplify detail on images which have little or no high-contrast areas and therefore diffuse components prevail. These filters are prone to moire patterns.
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