SMOOTHVISION HD

Anti-aliasing

The SMOOTHVISION HD implementation found in RADEON X800 builds largely on the anti-aliasing engine found in ATI’s existing DX9 products, which is currently regarded as the best-looking in the industry. Like previous designs, SMOOTHVISION HD’s anti-aliasing engine uses multi-sampling (particularly rotated-grid with gamma correction) with settings ranging from 2, 4, or 6 samples per pixel available.

When combined with ATI’s HYPERZ, which is a lossless compression technology used to compress the sampled color (the compression ratio ranges from 2:1 to 6:1 for color values) and Z values for each pixel, you can turn on AA without a huge performance hit. In fact, ATI has claimed 2xAA is practically free in high-end DX9 cards dating back to the RADEON 9700 PRO.

HYPERZ HD, a key component in improving anti-aliasing performance by optimizing memory bandwidth efficiency, now provides hierarchical Z-buffering at all resolutions, including 1920x1080 and 1600x1200. HYPERZ HD also features an improved Z-compression algorithm that can achieve up to 8:1 compression ratios for this operation, previously HYPERZ maxed out at 4:1 compression. This should improve performance at higher AA settings such as 6x.

Temporal anti-aliasing

Today’s anti-aliasing implementations rely on predefined sample patterns to improve image quality. This has worked out well, but rather than using static sampling that has already been defined, what if the board could choose from one of a few patterns to achieve even better-looking quality? This is where temporal AA comes in.

Temporal anti-aliasing is a new technique that uses programmable sample patterns that can be alternated on a per-frame basis. With each frame rendered using a different sampling pattern, this causes the image to look as if it has twice as many samples per pixel as it actually does. This blending effect can give 2x temporal multisample AA the look of standard 4x multisample AA, without the performance hit.

Temporal AA sampling

The drawback to this new AA method is frame rate. If the frame rate drops too low, the eye can perceive the slight fluctuations in the colors of anti-aliased edges, this results in flickering artifacts that can be quite distracting. Another downside is that v-sync must be enabled when temporal AA is used; a lot of competitive gamers like to disable v-sync for maximum frame rate, the higher the frame rate the smoother controls feel (up to a point which will vary depending on the particular title) in shooters such as Quake 3 and UT. If the frame rate does drop below a certain level, it can be disabled by the driver until frame rates improve to an acceptable level. If this occurs, the graphics card would revert back to traditional multisampling AA.

You can really see the difference temporal AA can make at settings of 85Hz and 100Hz, which are out of the reach of most LCD monitors and due to the nature of temporal AA, screenshots can’t accurately reproduce its effects, even providing video clips could be inaccurate. Therefore, the best way to see temporal AA is to sit in front of a graphics card that’s using it.

Anisotropic filtering

ATI has fine tuned its anisotropic filtering engine slightly in X800 and SMOOTHVISION HD. Anisotropic filtering levels of 2, 4, 8, or 16 texture samples per pixel are still supported (with bilinear samples taken in performance mode, and trilinear samples in the default quality mode) although SMOOTHVISION HD uses an improved algorithm for improved anisotropic filtering performance without negatively impacting image quality.

We’ll be providing screenshots of ATI’s X800 AA and AF quality in action later in this article.