Anisotropic Filtering

Anisotropic filtering is a filtering technique used in 3D computer graphics in which the number of texture samples generated changes depending on the angle that the surface to be rendered is in relative to the camera. Anisotropic filtering makes surfaces or patterns that are angled and farther from the camera look better and sharper than when this type of filter is not applied.

Anisotropic filtering is best explained with an example. Let’s say you are creating a computerized brick wall. the first thing you do is make a set of polygons that form the shape of the wall. Next, you cover that shape with a brick texture with a size of 512x512 pixels. The whole wall is covered by multiple instances of that texture.

If no MIP mapping is applied, the hardware is going to render the 512x512 texture samples and do extra work to scale that down when applying to other areas of the wall that should look smaller because of the distance and angle. MIP mapping makes this faster and less demanding by creating multiple samples of the texture, each one of which is smaller than the one before. The smaller sizes can be applied to the further areas that are angled in relation to the camera. If no anisotropic filtering is applied, the levels will look blurry and compressed because only a small number of samples are made available to be used over and over.

The number of samples taken depending on the steepness of the angle of the surface. When a surface is at a very shallow angle to the camera, only a few MIP map levels are required; more samples are needed as the angle gets steeper. Because of this variability, anisotropic filtering requires intense processing, but graphics hardware manufacturers are finding better ways and algorithms to make anisotropic filtering faster. Sometimes they also cut corners, sacrificing some level of detail in one portion to enhance another.

However, anisotropic filtering needs so much processing power that you have to weigh the perceived benefits of the visual quality against the impact that performance will have on the graphics card.