ATi & nVidia Anti-Aliasing Performance
Anti-Aliasing quality and performance compared while using anisotropic filtering
We have to name ATi the clear winner here: without anti-aliasing and with 2x anti-aliasing all chips perform similarly, or according to their relative prices. Once we go above 2x anti-aliasing the fun is over for the nVidia chips: while these are spending ever increasing amounts of performance for small gains in edge quality, the ATi chips are leaps and bounds ahead with their 4x and 6x modes, in both performance and edge smoothing quality. Using the performance figures of the Radeon 9800 Pro 256MB and the GeForceFX 5900 Ultra 256MB we can make the following comparison which presents the edge smoothing quality of various anti-aliasing modes alongside their respective performance penalties (for both smoothing and performance: higher is better; the performance percentage is normalised to the performance without anti-alising, 1024x768 and 1280x960/1024 were averaged):
This chart clearly demonstrates ATi's anti-aliasing leadership: with all of ATi's anti-aliasing modes, the performance hit is well justified by the achieved edge smoothing quality. With nVidia this only applies to the lesser modes 2x, 4x and 4xS, with these the performance hit fits the quality gain. We can't claim that for the higher modes of anti-aliasing at all, 12x and 8xS reduce performance far too much for their respective quality gains, they are quite inefficient.
nVidia's problem is, none of the efficient 2x, 4x and 4xS modes can compare to ATi's "middle of the road" mode 4x when it comes to edge smoothing quality. That means nVidia is only competitive in lower to medium quality anti-aliasing modes and falls short on higher quality modes, sometimes significantly so. As soon as higher anti-aliasing modes are required, ATi clearly edges out nVidia in both performance and image quality terms.
So currently ATi offers clearly better anti-aliasing than nVidia - at least in the high end segment where you can actually use 4x anti-aliasing or more in practice. nVidia would need to offer dramatically higher raw performance than ATi to make up for the difference in anti-aliasing - due to the current near-parity in "normal benchmarks" this seems out of the question.
This conclusion only theoretically applies to the mainstream segment, of course, as it's populated by cards that generally lack the performance for any anti-aliasing beyond 2x. And, as we have observed, at 2x anti-aliasing ATi and nVidia offer equal edge smoothing with only small differences in performance. The overall message - ATi's clear leadership in anti-aliasing - thus in practice only applies to high end cards, because that's what you need if you want to generally (be able to) use any more than 2x anti-aliasing.
In fact, the dramatic results we gathered have even surprised us: most hardware reviews on the web currently suggest that ATi and nVidia are about equal - also concernig anti-aliasing. This might stem from the fact that anti-aliasing modes with equal names are often compared directly - e.g. ATi's 4x anti-aliasing versus nVidia's 4x anti-aliasing.
But we may only compare two things if they are of equal value, in this case that would mean equal image quality or at least equal edge smoothing. The naming conventions for ATi's and nVidia's antialiasing modes alone, however, do not make a comparison valid, the quality offered by two anti-aliasing modes going by the same name can indeed be very different. In particular: testing ATi's 4x anti-aliasing versus nVidia's anti-aliasing is not a comparison with equal image quality, it's not even close. If you use image quality or the amount of edge smoothing as a basis for comparisons you end up at very different conclusions - as we did.
Of course there's a reason for this humiliating defeat of nVidia: since the GeForce 3 nVidia didn't work on anti-aliasing much at all. The GeForce4 Ti's Accuview anti-aliasing is just a very slight enhancement - and the GeForceFX did in fact add nothing to these technologies (yet it did gain some modes). The plethora of new modes offered on the GeForceFX are all driver controlled and are available and just as functional on older cards, down to the GeForce 3, if you're using a tweaking tool such as aTuner.
So when it comes to anti-aliasing, nVidia is still in 2001, the year the GeForce3 was launched. The next generation of graphics chips must change this, as ATi are far ahead already with the R3x0 series and they will certainly try to keep the heat turned up. We can only hope that nVidia will return the favor of more intelligent sampling grids, higher multisampling modes and gamma correction for anti-aliasing with the NV40, without removing the sometimes handy supersampling/multisampling hybrid modes from the drivers.