X-bit labs

ATI RADEON X800: R420 Totally Exposed (page 22)

Category: Video

by Tim Tscheblockov , Alexey Stepin , Anton Shilov

[ 05/04/2004 | 06:42 AM ]

Full-Screen Anti-Aliasing: Temporal Anti-Aliasing

In the end of the section devoted to SMOOTHVISION HD technologies from ATI, namely to anisotropic filtering and full-screen anti-aliasing, we would like to tell you a bit more about the new interesting anti-aliasing method. This approach has been introduced in the new ATI VPUs, namely in the freshly launched RADEON X800. we are going to talk about Temporal Anti-Aliasing.

The idea of temporal anti-aliasing is based on the fact that ATI graphics processors can control the samples location in case FSAA is enabled. In other words, the samples location is not preset on the hardware level once and for all, but is taken from a programmable table storing the samples positions inside a pixel.

The second fact used within the Temporal anti-aliasing approach is the existence of such a quality of human eyesight as inertia. When we look at a common CRT monitor, we do not perceive the sequence of frames as a discreet one, although the screen is shining not constantly but manages to light up and fade down a few dozens of times (or even hundreds of times) within each second.

Having combined these two facts together, ATI suggested an interesting way of improving the anti-aliasing quality without any additional computational expenses. If we reprogram the subpixels location for each frame drawn, we will be able to achieve subjectively better anti-aliasing quality, due to the inertial character of the human eyesight.

In other words, if we use for instance 2x mode, but in each even frame place two samples on one pixel diagonal, and in each odd frame – on the other pixel diagonal, then in case of high fps rate the human eye will “average” the even and odd frames and will perceive the image as if it were processed in 4x mode, providing higher visual quality.

ATI showed the location of samples in even and odd frames and the “seeming” result of the Temporal Anti-Aliasing as follows:

The maximum anti-aliasing quality, which can be obtained as a result of temporal anti-aliasing is achieved when we reprogram the samples location in 6x mode. Here the result that we see is equivalent to 12x multisampling. Not bad, eh?

Unfortunately, we cannot show you in this article how the temporal anti-aliasing actually works.

However, we can create and show two screenshots for each mode of the temporal anti-aliasing with different samples location.