ATI CrossFire Multi-GPU Technology Preview

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CrossFire Super AA Mode

Since end users will reportedly have new-found performance headroom available to them with ATi CrossFire technology, ATi also saw fit to enhance their Anti-Aliasing algorithms.  As such we learned about new AA sample patterns that will be offered in CrossFire setups.

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

Although ATi has dubbed their new AA modes as "Super AA", do not confuse this with full scene Super Sampling AA methods.  In actuality ATi's "Super AA" modes are a combination of Multi-Sample and Super Sample AA.  The benefits of these new modes are obviously targeted at superior image quality, with each card in a CrossFire configuration rendering the frame using different sample patterns.

As is shown here, ATi's new 10X Super AA mode is comprised of 8X Multi-Sample AA in combination with 2X Super Sample and their new 14X mode uses a 12X + 2X Super Sample pattern.  The benefit of Super Sample AA specifically is that it has the ability to smooth out surfaces in an entire scene unlike Multi-Sample, which really only works on edge surfaces.  Super Sample AA has the ability to work on transparent or opaque texels, as with those that comprise a surface texture for example.  There are however side-effects of Super Sample AA, since it blurs the edges of an entire scene, including those that you may want sharp, as with text for example.  This probably explains, in addition to the high demands that Super Sample puts on the graphics subsystem, why ATi is only going with 2X AA Super Sampling to complement Multi-Sample edge Anti-Aliasing.  All told, the final rendered output should, by all rights, be impressive.

AA Image Quality Comparisons
Supplied by ATi

ATi supplied us with a couple of example screen shots from Half Life 2 that show a comparison of their new 14X mode versus NVIDIA's competing 8X AA mode.

IMPORTANT UPDATE BELOW!

IMPORTANT UPDATE BELOW!

In the scenes above we are pointed to a two areas of interest.  Obviously the edge pixels, in the hotel sign, are smoother in the ATi provided shot but there is another benefit that may be more subtle but obvious once you know to look for it.  Your eyes have probably been getting used to the less detailed renderings of Multi-Sample AA with "micro-geometry" details.  If you take a close look at the telephone wires and the antennas on the roof-tops above you'll notice that the ATi 14X AA shots look more detailed and render-accurate as compared to the standard 8X AA shot.  This is impressive for sure but we'll have to see the results for ourselves in across a myriad of gaming conditions before we can make any conclusive statements here.  One area of concern would be 14X AA performance in more graphically challenging game titles like Doom 3, Far Cry or Splinter Cell Chaos Theory.  We shall see for ourselves soon enough.

**UPDATE:June 3, 2005
We tried to duplicate the screen shots that ATI supplied to us, and found that ATI seems to have misrepresented the micro-geometry detail of NVIDIA's 8X anti-aliasing method. The screen shots we took on our own with a GeForce 6800 GT, clearly show more detail than the screen shots distributed by ATI in their CrossFire presentation.  Take a look for yourself...


NVIDIA GeForce 6800
1024x768 8XAA / 16X Aniso

High Detail

NVIDIA GeForce 6800
1600x1200 8XAA / 16X Aniso

High Detail

NVIDIA GeForce 6800
1600x1200 8XAA / 16X Aniso

High Detail

We wandered around the same portion of the map ATI used for their screen shots at various resolutions with a GeForce 6800 GT installed into our test system and HL2 configured for high detail, and could not replicate ATI's screen shots.  Even at lower resolutions, the same portions of the antenna atop the hotel shown in the CrossFire 14X AA screen shot are visible on the GeForce. And with the resolution turned up to 1600x1200, the detail only got better. We even tried to move towards and away from the hotel from different angles and couldn't get the portions or the antennas missing in ATI's screen shots to disappear.  So, while ATI's new 14X AA method enabled by CrossFire may provide more micro-detail than other AA methods that use fewer samples, which seems evident in the edge details on the hotel sign, the difference between NVIDIA's 8X AA and CrossFire's 14X AA as demonstrated by ATI don't seem to be indicative of actual in-game images when comparable detail settings are used.

Finally, we contacted ATi for comment on this issue that we discovered and they agreed they too could not reproduce the lack of detail that is represented in the NVIDIA screen shot they provided us above, although they assured there was no intention of misleading us with these competitive image quality comparisons.  This isn't the first and probably won't be the last time we will be witness to over-zealous marketing efforts, whether accdidental or intentional. Regardless, we hope to be able to filter through this sort of thing for you, the reader, as we have here, in the future.


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