Test notes
NVIDIA's previous generation of cards presented a couple of intriguing problems for benchmarking. Most prominent among those, perhaps, was NVIDIA's use of an "optimized" method of trilinear filtering, a common texture filtering technique. This "optimized" mode reduces image quality for the sake of additional performance, and over time, it has earned the nickname "brilinear" filtering, because it seems to be a halfway version of real trilinear, with some proximity to bilinear filtering only. Through the course of multiple driver revisions, NVIDIA introduced this new technique, pledged to make it a driver checkbox option, made it a driver checkbox option, turned it on selectively in spite of the driver checkbox setting, and removed the checkbox from the driver.

All of this drama has presented a conundrum for reviewers, because the change really does influence the card's visual output, if only slightly, and its performance, mildly but perhaps a little less slightly. For many people, some of this stuff must sound like arguing over how many angels can fit on the head of a pin, but we do try to perform apples-to-apples comparisons whenever possible. Fortunately, NVIDIA has provided a checkbox in its NV40 drivers that disables "trilinear optimizations."

The control panel allows for disabling "brilinear" on the GeForce 6800 Ultra

I will show you the visual and performance differences between "brilinear" and trilinear filtering in the course of this review, so you can see what you think of it. For the sake of fairness, we disabled NVIDIA's trilinear optimizations on NV40 for the bulk of our comparative benchmarks testing. ATI's Radeon 9800 XT produces very similar image output to the GeForce 6800 Ultra with trilinear optimizations disabled, as you will see.

Unfortunately, NVIDIA's 60.72 drivers do not provide the option of disabling trilinear optimizations on the GeForce FX 5950 Ultra, so we were unable to test NVIDIA's previous generation card at the same image quality as its replacement and its primary competitor.

The default setting is "Quality," which allows adaptive anisotropic filtering

NVIDIA was also kind enough to expose a setting in its driver that allows the user to disable its adaptive anisotropic filtering optimizations by choosing "High quality" image settings. In this case, both ATI and NVIDIA use adaptive aniso, so disabling this optimization wouldn't really be fair. Also, I spent some time trying to find visual difference between NVIDIA's adaptive aniso and non-adaptive aniso (using different angles of inclination, looking for mip-map level of detail changes, doing mathematical "diff" operations between screenshots) and frankly, I didn't find much of anything. I did benchmark the two modes, as you'll see in our texture filtering section, but I could find no reason not to leave NVIDIA's adaptive aniso turned on during our tests.

In the end, none of these settings impact performance more than a few percentage points, and the GeForce 6800 Ultra doesn't need to worry about its handicap versus the previous generation of cards.