Texture filtering is one of the most fundamental features required to present the sweet looking 3D graphics we're accustomed to in today's titles, hence we've decided to write a little something on the subject.

Texture filtering comes in several different flavors with the three most common being point-sampling, bi-linear filtering and tri-linear filtering. Bi-linear filtering is the method that is more or less a set standard today, often accompanied by something called mip-mapping. Tri-linear filtering is something of a "high-quality" mode used to enhance visual realism yet another notch but it usually comes with a slight speed penalty (more on that later). Point sampling is rare these days in 3D accelerated software but if you run a game via software rendering you're more than likely to come across the results of this filtering method (or lack off).

Bi-linear texture filtering Bi-linear filtering, as mentioned, is more or less the standard today and is supported by just about every 3D accelerator on the market. When bi-linear filtering the accelerator uses an interpolation method to produce smooth transitions between different pixels in the source texture, this is done by sampling the four closest pixels of the source texture (or most suitable mip-map) and interpolating these values before rendering each single texel on screen.

Tri-linear texture filtering Tri-linear filtering bares much in common with Bi-linear filtering but in addition to doing just what Bi-linear filtering does tri-linear filtering also uses the four closest pixels in the second most suitable mip-map to produce smoother transitions between mip-map levels. All in all tri-linear filtering samples eight pixels and interpolates these before rendering, twice as much as bi-linear does. Tri-linear filtering always uses mip-mapping.

Anisotropic texture filtering Anisotropic filtering is the latest filtering type to be implemented in 3D accelerators and is even more advanced than tri-liner filtering, while tri-linear filtering is indeed capable of producing some fine visuals it only samples from a square area which in some cases is not the ideal way. Anisotropic (which means non-uniform shape) samples from even more than 8 pixels and depending on the degree of surface tilting on X - Y - Z in different shapes and there for can produce better quality, however anisotropic filtering requires even more fillrate than tri-linear filtering does which means it is slower.

Mip-mapping Mip-mapping is a technique where several versions of the same texture are used to represent this texture on screen at different distances, further away a smaller version of the texture is used and closer a bigger one. Mip-mapping can be used regardless of filtering method. The advantages of using Mip-mapping lies mainly in that it reduces memory bandwidth requirements of rendering but it also offers better quality in the rendered image.