ATI Radeon X1800 XT CrossFire Evaluation

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CrossFire AA: Image Quality

We've already explained how ATI's 'Super-AA' modes work in our initial CrossFire Technology Preview and X850 XT CrossFire piece, but we thought we'd give you all a quick refresher here as well. Essentially, Super-AA works by blending the frames rendered on each card together in the CrossFire Edition (Master) card's compositing engine. The end result is an effective increase in the number of samples used to anti-alias the scene.

New ATi Super AA Modes
Not to be confused with full Super Sample AA

The new Super-AA modes offered by CrossFire are 8X AA, 10X AA, 12X AA, and 14X AA. 8X Super-AA is the result of a blend of 4X multi-sample AA being used on each card, with each one using a different sample pattern. 12X Super-AA is very similar, but in this mode ATI's 6X multi-sample AA algorithm is used on each card, before they're blended together in the compositing engine. 10X AA and 14X AA, however, are somewhat different. In these modes, an additional level of anti-aliasing is applied to the image, in the form of 2X super-sample AA. Unlike MSAA, which only works on polygon edges, Super-Sample AA can reduce the appearance of jaggies in an entire scene, even on transparent textures like those used to simulate vegetation or a chain-link fence, for example. 10X Super-AA is basically 8X AA plus 2X super-sample AA, and 14X Super-AA is 12X AA plus 2X super-sample AA.

An additional benefit to the new compositing engine used on the X1800 XT CrossFire Edition Master card is that it can perform the blend operation at full-speed, for increased performance.

Half Life 2 Image Quality Analysis: Anti-Aliasing
NVIDIA vs. ATI

We spent some time analyzing the CrossFire X1800 XT's in-game image quality versus the best NVIDIA currently has to offer, a GeForce 7800 GTX SLI configuration. We used the "background 2" map in Half-Life 2 to get a feel for how each configuration's anti-aliasing algorithm's affected the scene.

NVIDIA GeForce 7800 GTX SLIAA Screenshots

GeForce 7800 GTX SLI
1280x1024 - No AA

GeForce 7800 GTX SLI
1280x1024 - 4x AA

GeForce 7800 GTX SLI
1280x1024 - SLI 8X AA

GeForce 7800 GTX SLI
1280x1024 - SLI 16x AA

ATI Radeon X1800 XT CrossFire AA Screenshots

Radeon X1800 XT CrossFire
1280x1024 - 8x AA

Radeon X1800 XT CrossFire
1280x1024 - 10x AA

Radeon X1800 XT CrossFire
1280x1024 - 12x AA

Radeon X1800 XT CrossFire
1280x1024 - 14x AA

We've included "No AA" and "4x AA" shots using a pair of GeForce 7800 GTX cards above, but these images are strictly here to maintain symmetry on the page. :)  The "real" comparison here is between NVIDIA's SLI8X and SLI16X modes versus ATI's 8X through 14X Super-AA.

If you direct your attention to the water-tower and crane in the background of the images, and the grass and tree in the forefront on the left, the impact anti-aliasing has on image quality is readily apparent. What'll you see if you browse through the images is that both platforms produce very good images and it's difficult to say with any conviction that one is any better than the other. Our favorites of the bunch are ATI's 10X and 14X modes, however, as they do the best job with micro-detail, and also clean up the jaggies in the grass as well. There is an obvious issue that still exists within ATI's drivers that causes the edge of the water to render incorrectly though at higher AA levels. This should be fixed in a future driver release.


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