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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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  • Kiste - Monday, March 05, 2012 - link

    So, how many people do you know who would spend a few hundred bucks for a performance "sidegrade" that saves them a few bucks per year on their energy bill?

    Price/performance is still the relevant metric for most people, with everything else being secondary. Not unimportant, but secondary. Noise can also be addressed on cards with high power draw by buying a card with a custom cooler or using a 3rd party cooler.
    Reply
  • Kaboose - Monday, March 05, 2012 - link

    Some people are just entering the market, some people are coming from 3+ generations ago, some people are looking for HTPC's that can game and need low power and low temp cards that provide solid performance. It isn't a sidegrade for someone who is coming from integrated graphics or maybe a 7800GT etc. It is easy to think that everyone who buys these types of GPU's are knowledgeable and already have high performing GPU's. But that just isn't the case a lot of the time. If you have a high end 5xxx or a mid-high range 6xxx GPU already then there is no reason to upgrade, frankly with the 68xx series AMD isn't looking to grab that market. Reply
  • Kiste - Monday, March 05, 2012 - link

    If you're looking for great price/performance, there are plenty of cards that offer more bang for your bucks.

    If you're looking for raw performance, you look elsewhere, too.

    Though I'll happily concede that the 7850/7870 are great absolutely fabulous for everyone who is building a "HTPC that can game".
    Reply
  • medi01 - Monday, March 05, 2012 - link

    And exactly where do you look for raw performance, pretty please? Maybe at nVidia 570, that costs 80$, consumes more energy yet is outperformed in most tests by 7850? Reply
  • Kiste - Monday, March 05, 2012 - link

    Where would you look for raw performance? How about the 79xx line?

    And what the hell are you talking about anyway? The 7850 does not "outperform" the 570 in most tests, unless you're again back at comparing an overclocked card to a non-overclocked card. Most 570 cards can do a 15-20% OC easily, btw.

    Hell, I bought my GTX570 about 12 months ago for €289. And I'm supposed to be blown away by something like the 7870 in 2012?

    The GTX570 became available about 14 months ago. It took AMD 14 frigging month to come up with a card like the 7870 that is 9% faster on average at the same price point?

    Gee, what a marvel of technology.
    Reply
  • krumme - Monday, March 05, 2012 - link

    570 is 250% larger and 9% slower
    Its a giant leap
    talk about marvel of technology
    Your card is tech from stone age compared to a 7870.
    Old tech is old
    Reply
  • SlyNine - Monday, March 05, 2012 - link

    I'm running a 5870 which is basically 75% the performance of a 7970, and I paid 379 for the 5870. Which is also 75% of the cost of a 7970. The price of a 7970 is basically the exact same price structure as the 2 1/2 year old 5870, So we are stuck where we were in 2009, yay.

    Yea we are sure moving forward...
    Reply
  • morfinx - Monday, March 05, 2012 - link

    75% performance of 7970 would mean that it's 33% faster than a 5870. And that's just not accurate. I have a 5870 as well, so I was paying a lot of attention on how much faster the 7970 is in various reviews. Everything I've read indicates that it's anywhere from 70-110% faster at 2560x1600 resolution (I run 3600x1920, so likely even even more of a difference). That's not even even considering the massive overclocking headroom of the 7970 vs barely any OC headroom of the 5870. Overclocked, a 7970 is easily twice as fast as a 5870. Reply
  • RaistlinZ - Monday, March 05, 2012 - link

    This is true. I came from a 5870 to a 7970 and at 2560x1600 the 7970 is easily twice as fast.

    And that's even before overclocking. My 5870 could barely overclock for crap, whereas my 7970 overclocks 27% on core and 18% on memory.
    Reply
  • SlyNine - Thursday, March 08, 2012 - link

    Not according to Anandtechs benchmarks. Reply

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