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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  • DeViLzzz - Monday, March 05, 2012 - link

    It is not the dumbest statement ever. Have you looked at multiple sites benchmarks ? Clearly a 2 GB 6950 Power Color flashed to a 6970 or a 6970 is worth keeping. Hardly an improvement over those situations for the price you would be paying for a 7870 and 7850. Reply
  • ExarKun333 - Monday, March 05, 2012 - link

    Then you don't follow the graphic card industry very well at all. Reply
  • MadAd - Monday, March 05, 2012 - link

    did i just read a different review? looking at this i did - Im on the 6950 and no theres not enough performance difference.

    also, comparing apples to oranges and saying theres a gain isnt going to work - if someones going to OC a 7*** then im sure they have also OC their 6***, so comparing a straight 6*** to the 7*** OC results and calling it a difference is smoke and mirrors.
    Reply
  • cactusdog - Monday, March 05, 2012 - link

    You guys dont get it. Why are you comparing the 7870 to a 6950? Should be the 6870 but even then The 7870 smashes the 6950 when overclocked. the 7870 performs like a stock 7970 when overclocked. You cant compare overclocking on the 6 series to the 7 series. The 7 series is the sandy bridge of GPUs.

    Why compare last gens high end to this gens mid range? If you have a 6950/6970 you should be looking at a 7950/7970. A 7950/7970 will give you 70% increase in performance when overclocked. AMD left heaps of overclocking headroom for easy overclocking.

    Sure, the price is a little high now, but just wait a few weeks until Nvidia cards arrive and prices will come down. New tech is always a little expensive when it first comes out but no one is forcing you to buy now. Just wait a couple of weeks
    Reply
  • Kiste - Tuesday, March 06, 2012 - link

    "Why compare last gens high end to this gens mid range?"

    Because were introduced at the same price point. Video card names/numbers are completely arbitrary, you have to compare cards at a given price point.
    Reply
  • xrror - Monday, March 05, 2012 - link

    So I have one the the early 6950 2GB cards unlocked to 1536 shaders, and a 935/1275 overclock.

    Running at 1920x1200 in skyrim with the high resolution texture packs from Bethesda starts to lag.

    Yes I'm being petty, but as a PC gaming smoe, I'm looking for a card that's under $300 that will dominate what I have.

    I can't find a confident vote for a strong successor in the sub $300 range to replace my current card.

    This makes me sad. Also with all the growing pains 69xx series had - and AMD's dumping of VLIW4 makes me pretty sure 69xx is a dead end for any future driver improvements.

    Maybe I can sell my 6950 for $100 to subsidize a 79xx or a Kepler?
    Reply
  • Zoomer - Wednesday, March 07, 2012 - link

    I'll take it. Reply
  • mpschan - Monday, March 05, 2012 - link

    I'd tend to agree with your assessment. Only those looking for bleeding edge performance should consider the upgrade to the 7900 series.

    The price/performance curve is a little disappointing, but not unexpected. This is what happens when you:

    a) Move to a new process
    b) Implement a new architecture
    c) (Most importantly) Have no competition

    They need to make their money back on the first two, and having no competition allows them to do that and then some.

    But look at the thermals and power draw. Decreased power usage with a small gain in performance? Where have I seen that before ... oh I know, Intel!

    Welcome to tick-tock folks. They took their process shrink and used it to allow them to draw less power, not tear up the performance charts.

    This means the next generation on 28nm has room to expand. 1280 SP for the 7870 can be 1600 for the 8870. A 212mm2 die can be 300mm2. 190w can be 220w.

    Ultimately the performance of these cards will come down to power drawn. The huge jumps in performance that we used to see existed because of drastically improving fabrication technologies combined with better ways of rendering screens. I think those days will be few and far between now.
    Reply
  • arjuna1 - Monday, March 05, 2012 - link

    You have a point, this generation is not worth spending the $$$ to "sidegrade". I don't kepler doing anything to change that other than forcing AMD to have decent prices. Reply
  • cactusdog - Monday, March 05, 2012 - link

    How is a 7950/7970 a "sidegrade"?? To a 6950/6970? Its a massive performance increase. If you have a highend 6 series GPU you should be looking at highend 7 series. Not midrange. Reply

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