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High IQ: AMD Fixes Texture Filtering and Adds Morphological AA

“There’s nowhere left to go for quality beyond angle-independent filtering at the moment.”

With the launch of the 5800 series last year, I had high praise for AMD’s anisotropic filtering. AMD brought truly angle-independent filtering to gaming (and are still the only game in town), putting an end to angle-dependent deficiencies and especially AMD’s poor AF on the 4800 series. At both the 5800 series launch and the GTX 480 launch, I’ve said that I’ve been unable to find a meaningful difference or deficiency in AMD’s filtering quality, and NVIDIA was only deficienct by being not quite angle-independent. I have held – and continued to hold until last week – the opinion that there’s no practical difference between the two.

It turns out I was wrong. Whoops.

The same week as when I went down to Los Angeles for AMD’s 6800 series press event, a reader sent me a link to a couple of forum topics discussing AF quality. While I still think most of the differences are superficial, there was one shot comparing AMD and NVIDIA that caught my attention: Trackmania.

Poor high frequency filtering

The shot clearly shows a transition between mipmaps on the road, something filtering is supposed to resolve. In this case it’s not a superficial difference; it’s very noticeable and very annoying.

AMD appears to agree with everyone else. As it turns out their texture mapping units on the 5000 series really do have an issue with texture filtering, specifically when it comes to “noisy” textures with complex regular patterns. AMD’s texture filtering algorithm was stumbling here and not properly blending the transitions between the mipmaps of these textures, resulting in the kind of visible transitions that we saw in the above Trackmania screenshot.

Radeon HD 5870 Radeon HD 6870 GeForce GTX 480

So for the 6800 series, AMD has refined their texture filtering algorithm to better handle this case. Highly regular textures are now filtered properly so that there’s no longer a visible transition between them. As was the case when AMD added angle-independent filtering we can’t test the performance impact of this since we don’t have the ability to enable/disable this new filtering algorithm, but it should be free or close to it. In any case it doesn’t compromise AMD’s existing filtering features, and goes hand-in-hand with their existing angle-independent filtering.

At this point we’re still working on recreating the Trackmania scenario for a proper comparison (which we’ll add to this article when it’s done), but so far it looks good – we aren’t seeing the clear texture transitions that we do on the 5800 series. In an attempt to not make another foolish claim I’m not going to call it perfect, but from our testing we can’t find any clear game examples of where the 6870’s texture filtering is deficient compared to NVIDIA’s – they seem to be equals once again. And even the 5870 with its regular texture problem still does well in everything we’ve tested except Trackmania. As a result I don’t believe this change will be the deciding factor for most people besides the hardcore Trackmania players, but it’s always great to see progress on the texture filtering front.

Moving on from filtering, there’s the matter of anti-aliasing. AMD’s AA advantage from the launch of the 5800 series has evaporated over the last year with the introduction of the GeForce 400 series. With the GTX 480’s first major driver update we saw NVIDIA enable their transparency supersampling mode for DX10 games, on top of their existing ability to use CSAA coverage samples for Alpha To Coverage sampling. The result was that under DX10 NVIDIA has a clear advantage in heavily aliased games such as Crysis and Bad Company 2, where TrSS could smooth out many of the jaggies for a moderate but reasonable performance hit.

For the 6800 series AMD is once again working on their AA quality. While not necessarily a response to NVIDIA’s DX10/DX11 TrSS/SSAA abilities, AMD is introducing a new AA mode, Morphological Anti-Aliasing (MLAA), which should make them competitive with NVIDIA on DX10/DX11 games.

In a nutshell, MLAA is a post-process anti-aliasing filter. Traditional AA modes operate on an image before it’s done rendering and all of the rendering data is thrown away; MSAA for example works on polygon edges, and even TrSS needs to know where alpha covered textures are. MLAA on the other hand is applied to the final image after rendering, with no background knowledge of how it’s rendered. Specifically MLAA is looking for certain types of high-contrast boundaries, and when it finds them it treats them as if they were an aliasing artifact and blends the surrounding pixels to reduce the contrast and remove the aliasing.

MLAA is not a new AA method, but it is the first time we’re seeing it on a PC video card. It’s already in use on video game consoles, where it’s a cheap way to implement AA without requiring the kind of memory bandwidth MSAA requires. In fact it’s an all-around cheap way to perform AA, as it doesn’t require too much computational time either.

For the 6800 series, AMD is implementing MLAA as the ultimate solution to anti-aliasing. Because it’s a post-processing filter, it is API-agonistic, and will work with everything. Deferred rendering? Check. Alpha textures? Done. Screwball games like Bad Company 2 that alias everywhere? Can do! And it should be fast too; AMD says it’s no worse than tier Edge Detect AA mode.

So what’s the catch? The catch is that it’s a post-processing filter; it’s not genuine anti-aliasing as we know it because it’s not operating on the scene as its being rendered. Where traditional AA uses the rendering data to determine exactly what, where, and how to anti-alias things, MLAA is effectively a best-guess at anti-aliasing the final image. Based on what we’ve seen so far we expect that it’s going to try to anti-alias things from time to time that don’t need it, and that the resulting edges won’t be quite as well blended as with MSAA/SSAA. SSAA is still going to offer the best image quality (and this is something AMD has available under DX9), while MSAA + transparency/adaptive anti-aliasing will be the next best method.

Unfortunately AMD only delivered the drivers that enable MLAA yesterday, so we haven’t had a chance to go over the quality of MLAA in-depth. As it’s a post-processing filter we can actually see exactly how it affects images (AMD provides a handy tool to do this)  so we’ll update this article shortly with our findings.

Finally, for those of you curious how this is being handled internally, this is actually being done by AMD’s drivers through a DirectCompute shader. Furthermore they’re taking heavy advantage of the Local Data Store of their SIMD design to keep adjacent pixels in memory to speed it up, with this being the biggest reason why it has such a low amount of overhead. Since it’s a Compute Shader, this also means that it should be capable of being back-ported to the 5000 series, although AMD has not committed to this yet. There doesn’t appear to be a technical reason why this isn’t possible, so ultimately it’s up to AMD and if they want to use it to drive 6800 series sales over 5000 series sales.

Seeing the Present: HDMI 1.4a, UVD3, and Display Correction What’s In a Name?
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  • Ryan Smith - Friday, October 22, 2010 - link

    Quality is unchanged. UVD 3 adds a few fixed function blocks, but quality is a matter of post-processing and hence affected by the drivers once you have sufficient shader power to do all the post-processing. Reply
  • Pastuch - Friday, October 22, 2010 - link

    I posted about this earlier but my post was deleted.

    Ryan there is a ton of HTPC users on this site.

    1. Exactly how long is the Radeon 6870/6850 vs the GTX 460?

    2. How does the GTX460 compare to the Radeon 6 series regarding bitstreaming high def audio?

    3. How UVD3 post-processing compare to Nvidias?
    Reply
  • Ryan Smith - Friday, October 22, 2010 - link

    It's exactly the same as this: http://www.anandtech.com/show/3973/nvidias-geforce... Reply
  • HigherGround - Friday, October 22, 2010 - link

    Why was EVGA card included in this test? The rest of the field is generic (non OC, no brand), so why included an OC card, which skews the readers perspective? Pretty sure EVGA paid you to included its top OC card in this review ... Reply
  • Parhel - Friday, October 22, 2010 - link

    No, NVidia paid them to include it. NVidia sends "guidelines" to all the hardware review sites, telling them what settings to use and which cards to use in the comparison. In the guidelines for today's review was to use the EVGA GTX 460 FTW, and and site you see using it is essentially a paid NVidia shill.

    I could care less about ATI vs NVidia, as I'm not really a gamer, but I'm very disappointed today to see my long time favorite hardware site stooping to this level. In the end, it gives consumers bad information, which should be antithetical to the purpose of a site like this.
    Reply
  • AtwaterFS - Friday, October 22, 2010 - link

    I agree, this site is typically class-leading, but this article give AnandTech a bit of a black eye and the results dont particularly jive with "un-biased" sites like HardOCP. Reply
  • DrKlahn - Friday, October 22, 2010 - link

    I was going to post the same thing. As a long time reader of this site, I was very disappointed with the decision to include the overclocked card. Either the ATI cards should have been overclocked and their results provided in every test or it should have been excluded as per the normal benchmarking guidelines.

    I would have no issue with a followup or side article comparing factory overclocked offerings. But this is clearly bowing to pressure from Nvidia and I expected better of this site.
    Reply
  • aungee - Saturday, October 23, 2010 - link

    To Include the EVGA GTX 460 FTW was unfair and whether intentional or not it did spoil the launch party for AMD on this site to some degree. It would have been more appropriate to make a small mention of it's existence and to benchmark it in the future against any factory OC 6800 cards.

    After getting your head around the naming, AMD needs to be credited for bringing such a performance on only a 255 mm2 package (it even caused the price drop for the 530mm2 GTX 470) . AMD has headroom to drop the price of the 6800 cards so lets hope they do soon.
    Reply
  • tigersty1e - Friday, October 22, 2010 - link

    I couldn't find the clocks, but if you do include an OC'd card in your benches, you should give us the clocks. Reply
  • dertechie - Friday, October 22, 2010 - link

    850 MHz Core, 1700 MHz shaders, 4 GHz Memory, up from 675 MHz Core, 1350 MHz shaders, 3.6 GHz Memory.

    That's a 26% Core OC and an 11% Memory OC. However, the cost has been OC'd too, the FTW card costs the same $240 as the stock Radeon 6870.
    Reply

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