ATI's Optimized Texture Filtering Called Into Question

Angle Optimization In Anisotropic Filtering

Let's move to a new chapter in today's optimizations, those of adaptive, angle optimized anisotropic filtering. They have been in use for a long time in ATI cards. NVIDIA practically adopted this technology with the GeForce 6800. Here, too, it is a matter of saving computing time. A surface is thus anisotropically filtered with a varying factor depending on the angle to the viewer.

This screenshot shows the 8x anisotropic filtering result of Microsoft Refrast. It's not optimally smooth in all angles, but almost.

The result of the ATi X800 with heavy angle optimization. Only a few areas get 8x anisotropic filtering. Most are 4x or less. The GeForce 6800 shows a similar behavior.

The reasons for this are plausible. For example, if you stand directly in front of a wall, you will not need 16x anisotropic filtering. With 2x filtering the result will be the same. You can thus set up the optimization so that the available computing time is used better and more efficiently and is not wasted on places where higher filtering would not produce a better result anyway. If you set the 16x filtering in the driver, you still only get this degree of filtering in certain places.

In practice, this functions rather well. However, in specific cases, for example when the player is standing next to an irregular mountain face, this can certainly cause a loss in quality. Whether or not this bothers someone is frankly a matter of taste. Even so, you still get a considerably higher frame rate this way. It would be nice if the user were given the choice of whether to use this optimization or not.

Moreover, the level of anisotropic filtering depends on the location and distance of a surface from the viewer.