Anti-Aliasing Analysis, Part 1: Settings And Surprises

Coverage Sampling Modes: Nvidia’s CSAA And AMD’s EQAA

With the GeForce 8 series, Nvidia introduced a new technique it called coverage sampling anti-aliasing (CSAA). Essentially, CSAA is traditional MSAA with extra coverage samples added. Coverage samples test to see whether a polygon is present at the location of the sample, and these can be used to weight the calculation when determining the final color of the pixel. Because coverage samples are relatively easy for the hardware to gather, the result can be an increase in quality that requires a relatively small performance overhead compared to MSAA samples. Unfortunately, the value of coverage samples depends on the makeup of the individual pixel, so the resulting increase in quality ranges from some to none at all.

Starting with the Radeon HD 6900 series, AMD now offers enhanced quality anti-aliasing (EQAA), a mode that is essentially identical to Nvidia’s CSAA. Unfortunately, the ROPs in the rest of the company's Radeon portfolio (even including the Radeon HD 6800-series cards) are not able to handle EQAA, so most AMD graphics card owners won’t be able to take advantage of this feature. Nvidia owners have more flexibility in this respect, as the GeForce 8000, 9000, 200, 300, 400, and 500 series enable CSAA support.

Mode Confusion

Unfortunately, Nvidia has a somewhat inconsistent method of designating its anti-aliasing modes, with numbers sometimes indicating total MSAA samples, and at other times indicating a sum of MSAA and coverage samples. The suffix “Q” indicates pure MSAA in the case of Nvidia’s 8xQ setting, but the 16xQ setting has 8xMSAA plus eight coverage samples. This leads to confusing situations, as the 8x setting in the Nvidia driver does not represent 8x MSAA, but signifies 4x MSAA plus four coverage samples.

AMD deserves some kudos here for sticking to a naming convention that makes perfect sense. AMD’s level always indicates the number of MSAA samples, while the EQ suffix means the same number of coverage samples is added. For example, AMD’s 8x setting designates eight MSAA samples. But the 8xEQ setting designates eight MSAA samples plus eight additional coverage samples.

The following chart demonstrates how AMD and Nvidia anti-aliasing modes correspond to each other:

GeForce CSAA vs. Radeon EQAA
Anti-aliasing Levels
GeForce
Driver Mode
Combined Color/Coverage Samples
+ Extra Coverage Samples
Radeon
Driver Mode
2x
2+0
2x
n/a
2+2
2xEQ
4x
4+0
4x
8x
4+4
4xEQ
16x
4+12
n/a
8xQ
8+0
8x
16xQ
8+8
8xEQ
32x
8+24
n/a
n/a
16+0
16x


Coverage Sampling Image Comparisons

Coverage samples offer a relatively limited increase in overall anti-aliasing-based image quality on both Nvidia and AMD graphics hardware. Certainly, more MSAA samples result in a definite visual improvement, while more coverage samples can result in no quality increase at all. It is because of this that we’re not fans of Nvidia’s naming scheme, where 16x provides obviously lower quality compared to what 8xQ offers.

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  • PERTAMAX gan. .
    -4
  • Awesome article. I am unfortunately not one of the elite few who know all the ins and outs of graphics performance, so this was very enlightening for me.
    8
  • Great article, very informative. I've never really used forced anti-aliasing through the driver, and from what I've read it doesn't really sound like a good idea anyway, given the fact that most modern games provide adequate AA levels through in-game settings (these are usually better optimized as well). Seems like forced driver level AA is pretty hit-or-miss. With a few rare exceptions it just doesn't seem like it's worth the effort.

    ...went to the link for Tom's Geforce3 article. The good old Geforce3, now that takes me back.
    4
  • This is definitely one of the better articles I've read
    8
  • what are you talking about?
    we can still force Supersampling
    as of 266.58 on Nvidia cards
    0
  • Why does it say here, http://www.geforce.com/#/Optimize/Guides/AA-AF-guide (go to the next page of this article), that it internally renders the frame at a resolution 4 times greater? But according to the 2nd page of this article, it says that at x4 AA it only internally renders a frame at a resolution 2 times greater.
    1
  • Great article, but this is really something Nvidia and AMD will have to fix together with game developers...

    The settings I select in the driver control panel should apply without me having to worry about coverage samples, multi samples, DirectX versions or the alignment of the planets. It should just work.

    Similarly, any self-respecting game made in the last 6-8 years should have proper anti-aliasing options in its in-game menu. Not just an On/Off switch, but the full range of AA settings available with the video card being used.
    3
  • MrBonkBonkwhat are you talking about?we can still force Supersampling as of 266.58 on Nvidia cards



    IF the game lets it! Drivers trying to force AA doens't mean the game will allow it. If the game doesnt' support it your not goting to get tehy type of AA.

    Either way this AA fragmentation is almost as bad as all these custom versions of Driod.
    -1
  • Maybe I'm wrong, but no Batman or Mass Effect 2 forced AA settings?
    1
  • @army_ant7:

    Nvidia article is wrong, or at the very least semantically sloppy.

    4X samples generally means doubling of resolution for both axes. 4*(x*y)==(2*x)*(2*y).
    2
  • Quote:
    Nvidia article is wrong, or at the very least semantically sloppy. 4X samples generally means doubling of resolution for both axes. 4*(x*y)==(2*x)*(2*y).


    Thanks for the reply heycarnut.

    With that it mind, what does 2X sampling multiply the axes by?
    1
  • if the game doesn't support anti aliasing, forcing through the driver may or may not work, but the point here is that nvidia drivers still do support supersampling as opposed to that mentioned in the article.
    0
  • Nvidia is currently offering a SSAA tool for download. Its a bit primitive and just sets SSAA for all games.
    http://nvidia.custhelp.com/cgi-bin/nvidia.cfg/php/enduser/std_adp.php?p_faqid=2624
    0
  • Gr8 article. Thanks!
    0
  • Thanks for the great article Don.
    0
  • how about some benchmarks with the games that accepted forced driver settings? that way we can see if the in game setting is biased toward one card company. like left for dead 2, benchmarks of the ingame setting for 2x,4x,8x. then benchmarks of the driver setting 2x MSAA/SSAA, 4x MSAA/SSAA and so on. that way we can see if the game is being biased.
    1
  • Ive always wondered what was the difference between and what was better between application decided and driver based AA. In far cry 2 using my HD4870 The trees turned into green blobs using driver based AA but in game AA worked perfectly. Since then Ive just left the let the application decide box ticked and ignored Driver based. Can't wait for part 2 to see what gives the best result if it even works. Great work toms!!
    0
  • Nvidia Inspector (http://blog.orbmu2k.de/tools/nvidia-inspector-tool) is like the Nvidia control panel on steroids. It gives access to many more of the configuration options than the Nvidia control panel, like SSAA, several settings for transparency anti-aliasing, and a whole bunch of other advanced configuration options. I prefer it over nHancer (http://www.nhancer.com/), as I've had better luck with it in the past, but both should work. I'm somewhat surprised, though, that no one at Tom's Hardware actually used it to test out Nvidia SSAA, as I've had quite a lot of success with it.

    assmarMaybe I'm wrong, but no Batman or Mass Effect 2 forced AA settings?

    I used Nvidia Inspector on Mass Effect 1 and Mass Effect 2 to play the game with 2x2 SSAA (2x horizontal and 2x vertical), and it definitely works if you set it to force the game to use those settings. Forcing MSAA in those games didn't seem to work though, or if it did the effect wasn't noticeable enough to be worth it, not surprising considering some of the issues Unreal Engine games have with anti-aliasing. I didn't bother trying this with Batman because the built-in AA for the game looked fine.
    2
  • I can see the benefit from AA in the examples, but doesn't it make things look fuzzy? I suppose it's a necessary trade-off for now.
    0
  • army_ant7Why does it say here, http://www.geforce.com/#/Optimize/Guides/AA-AF-guide (go to the next page of this article), that it internally renders the frame at a resolution 4 times greater? But according to the 2nd page of this article, it says that at x4 AA it only internally renders a frame at a resolution 2 times greater.


    Depends on how you frame it I guess: when the dimensions are doubled, the area is quadrupled.

    Twice the size is four times the samples: Like a 2"x2" grid contains four square inches, and twice the size is 4"x4" but it contains 16 square inches... four times as much area, but only twice the size when you look at the dimensions.

    army_ant7With that it mind, what does 2X sampling multiply the axes by?


    1.5 times? :p

    It's probably easier to just think of the number as how many samples per pixel. 2xAA=2 samples per pixel, 4xAA=4 samples per pixel, etc...
    1