X-bit labs

Highly Defined: ATI Radeon HD 2000 Architecture Review (page 8)

Category: Video

by Anton Shilov , Yaroslav Lyssenko, Alexey Stepin

[ 05/15/2007 | 07:34 AM ]

Evolution of FSAA: Now Up To 24x!

Even though multisampling antialiasing provides optimal balance between image quality and performance hit, both Nvidia and ATI decided implement new full-scene antialiasing technologies into new DirectX 10-compatible graphics processors, as despite of improvements in display resolutions a lot of people demand higher quality of FSAA.

The new Radeon HD 2000 chips from ATI/AMD support a new method of antialiasing that the company calls custom-filter antialiasing (CFAA). In fact, CFAA includes three methods of antialiasing that are pretty different from each other:

• CFAA with wide tent filter;
• CFAA with narrow tent filter;
• CFAA with adaptive edge detect capability.

Both wide-tend and narrow-tent CFAA rely on programmable post-filters that samples sub-samples from outside a pixel. ATI claims that the method is fully programmable and that sub-samples have different weights, meaning that driver developers and software developers can control quality of antialiasing. Even though the method has several advantages, its main disadvantage – sampling of sub-pixels from outside pixel – is blurring of the whole image, which can negatively affect the final picture.

A more promising FSAA technique implemented into Radeon HD 2000 hardware is adaptive edge detect filter, which, according to developers, can perform edge detection pass on rendered image and then applying antialiasing with increased amount of samples onto pixels that contrast with each other more than the rest, e.g., edges or textures with large drawings. Potentially, this may reduce texture shimmering and avoid blurring, however, this needs to be checked in practice, as, for example, textures with small details may still be “antialiased” too much and will get blurry. Unfortunately, current official drivers for Radeon HD 2000 do not support adaptive edge detect filter.