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Further Image Quality Improvements: SSAA LOD Bias and MLAA 2.0

The Southern Islands launch has been a bit atypical in that AMD has been continuing to introduce new AA features well after the hardware itself has shipped. The first major update to the 7900 series drivers brought with it super sample anti-aliasing (SSAA) support for DX10+, and starting with the Catalyst 12.3 beta later this month AMD is turning their eye towards further improvements for both SSAA and Morphological AA (MLAA).

On the SSAA side of things, since Catalyst 9.11 AMD has implemented an automatic negative Level Of Detail (LOD) bias in their drivers that gets triggered when using SSAA. As SSAA oversamples every aspect of a scene – including textures – it can filter out high frequency details in the process. By using a negative LOD bias, you can in turn cause the renderer to use higher resolution textures closer to the viewer, which is how AMD combats this effect.

With AMD’s initial release of DX10+ SSAA support for the 7900 series they enabled SSAA DX10+ games, but they did not completely port over every aspect of their DX9 SSAA implementation. In this case while there was a negative LOD bias for DX9 there was no such bias in place for DX10+. Starting with Catalyst 12.3 AMD’s drivers have a similar negative LOD bias for DX10+ SSAA, which will bring it fully on par with their DX9 SSAA implementation.

As far as performance and image quality goes, the impact to both is generally minimal. The negative LOD bias slightly increases the use of higher resolution textures, and thereby increases the amount of texels to be fetched, but in our tests the performance difference was non-existent. For that matter in our tests image quality didn’t significantly change due to the LOD bias. It definitely makes textures a bit sharper, but it’s a very subtle effect.


Original uncropped screenshots

4x SSAA 4x SSAA w/LOD Bias

Moving on, AMD’s other AA change is to Morphological AA, their post-process pseudo-AA method. AMD first introduced MLAA back in 2010 with the 6800 series, and while they were breaking ground in the PC space with a post-process AA filter, game developers quickly took the initiative 2011 to implement post-process AA directly into their games, which allowed it to be applied before HUD elements were drawn and avoiding the blurring of those elements.

Since then AMD has been working on refining their MLAA implementation, which will be replacing MLAA 1.0 and is being launched as MLAA 2.0. In short, MLAA 2.0 is supposed to be faster and have better image quality than MLAA 1.0, reflecting the very rapid pace of development for post-process AA over the last year and a half.

As far as performance goes the performance claims are definitely true. We ran a quick selection of our benchmarks with MLAA 1.0 and MLAA 2.0, and the performance difference between the two is staggering at times. Whereas MLAA 1.0 had a significant (20%+) performance hit in all 3 games we tested, MLAA 2.0 has virtually no performance hit (<5%) in 2 of the 3 games we tested, and in the 3rd game (Portal 2) the performance hit is still reduced by some. This largely reflects the advancements we’ve seen with games that implement their own post-process AA methods, which is that post-process AA is nearly free in most games.

Radeon HD 7970 MLAA Performance
  4x MSAA 4x MSAA + MLAA 1.0 4x MSAA + MLAA 2.0
Crysis: Warhead 54.7

43.5

53.2
DiRT 3 85.9 49.5 78.5
Portal 2 113.1 88.3 92

As for image quality, that’s not quite as straightforward. Since MLAA does not have access to any depth data and operates solely on the rendered image, it’s effectively a smart blur filter. Consequently like any post-process AA method there is a need to balance the blurring of aliased edges with the unintentional burring of textures and other objects, so quality is largely a product of how much burring you’re willing to put up for any given amount of de-aliasing. In other words, it’s largely subjective.


Original uncropped screenshots

  Batman AC #1 Batman AC #2 Crysis: Warhead Portal 2
MLAA 1.0 Old MLAA Old MLAA Old MLAA Old MLAA
MLAA 2.0 New MLAA New MLAA New MLAA New MLAA

From our tests, the one thing that MLAA 2.0 is clearly better at is identifying HUD elements in order to avoid blurring them – Portal 2 in particular showcases this well. Otherwise it’s a tossup; overall MLAA 2.0 appears to be less overbearing, but looking at Portal 2 again it ends up leaving aliasing that MLAA 1.0 resolved. Again this is purely subjective, but MLAA 2.0 appears to cause less image blurring at a cost of less de-aliasing of obvious aliasing artifacts. Whether that’s an improvement or not is left as an exercise to the reader.

Meet The Radeon HD 7870 & Radeon HD 7850 The Test
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  • slypher1024 - Thursday, March 08, 2012 - link

    Well said bro...

    Its like Nvidia and Amd secretly team up to maximizing profits.. AMD launch now, over price the product, Nvidia hold out for like 3-5 months, then launches a more powerful product knowing all too well that yes AMD will drop there prices, but we have the more powerful hardware so, persons will still gobble it up..

    You would think with the launch of a new product line, AMD would drop the price significantly so it can encourage customer to buy off the remaining stock .
    Reply
  • IceDread - Thursday, March 08, 2012 - link

    I do not think it's ok to skip hd 7970 but include nvidia 580. This makes anandtech look like it favors nvidia over amd and the entire site can be questioned. Reply
  • warmbit - Tuesday, April 10, 2012 - link

    Here is the link to an interesting overview performance 7870 and 7850 of 5 Web sites competing Nvidia cards - GTX580 and GTX570 and penalties of the previous generation AMD - 6970 and 6950.

    Analysis of the results of the Radeon 7870 and 7850 in 12 games and 5 resolutions:
    http://translate.google.pl/translate?hl=pl&sl=...

    You will know the relationship between average interest rates these cards and you will find out in which graphics card is better in the game and resolution.
    Reply

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