AMD’s Radeon HD 6870 & 6850: Renewing Competition in the Mid-Range Market
by Ryan Smith on October 21, 2010 10:08 PM ESTHigh 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.
Facebook
Twitter
RSS
197 Comments
View All Comments
GeorgeH - Friday, October 22, 2010 - link
WRT comments complaining about the OC 460 -It's been clear from the 460 launch that a fully enabled and/or higher clocked 460 would compete very well with a 470. It would have been stupid for NVIDIA to release such a card, though - it would have made the already expensive GF100 even more so by eliminating a way to get rid of their supply of slightly defective GF100 chips (as with the 465) and there was no competitive reason to release a 460+.
Now that there is a competitive reason to release one, do you really think Nvidia is going to sit still and take losses (or damn close to it) on the 470 when it has the capability of launching a 460+? Do you really think that Nvidia still can't make fully functional GF104 chips? Including the OC 460 is almost certainly Ryan's way of hinting without hinting (NDAs being what they are) what Nvdia is prepping for release.
(And if you really think AT is anyone's shill, you're obviously very new to AT.)
AnandThenMan - Friday, October 22, 2010 - link
"And if you really think AT is anyone's shill, you're obviously very new to AT."Going directly against admitted editorial policy doesn't exactly bolster your argument now does it. As for your comment about a 460+ or whatever you were trying to say, who cares? Reviews are supposed to be about hardware that is available to everyone now, not some theoretical card in the future.
MGSsancho - Friday, October 22, 2010 - link
A vendor could just as likely sell an overclocked 470 card as well as a 480. But I think you made the right assumption that team green might be releasing overclocked cards that all have a minimum of 1gb of ram to make it look like their cards are faster than team red's. maybe it will be for near equal price points, the green cards will all be 20~30% overclocked to make it look like they are 10% faster than the red offerings at similar prices. Red cards could just be sold over clocked as well (we have to wait a bit more to see how well they overclock). All of this does not really matter. In the end of the day, buyers will look at whats the fastest product they can purchase at their price point. Maybe secondly they will notice that hey this thing gets hot and is very loud and just blindly blaming the green/red suits and thirdly they will look at features. Who really knows.Personally I purchase the slightly slower products then over clock them myself if i find a game that needs it. I would rather have the headroom vs buying a card that is always going to be hot enough to rival volcanoes even if it is factory warrantied.
Golgatha - Friday, October 22, 2010 - link
The nVidia volcanoes comment is really, really overstated. I have a mid-tower case with a 120mm exhaust and 2x92mm intakes (Antec Solo for reference), and a GTX 480. None of these case fans are high performance fans. Under very stressful gaming conditions, I hit in the 80-85°C range, and Folding@Home's GPU3 client will get it up to 91°C under 100% torturous load.Although I don't like the power consumption of the GTX 480 for environmental reasons, it is rock solid stable, has none of the drawbacks of multi-GPU setups (I actually downgraded from a Crossfire 5850 setup due to game crashing and rendering issues), and it seems to be top dog in a lot of cases when it comes to minimum FPS (even when compared to multi-GPU setups).
Parhel - Friday, October 22, 2010 - link
"And if you really think AT is anyone's shill, you're obviously very new to AT"I think you're referring to me, since I'm the one who used the word "shill." Let me tell you, I've been reading AT since before Tom's Hardware sucked, and that's a loooong time.
If I were going to buy a card today, I'd buy the $180 GTX 460 1GB, no question. I'm not an AMD fan, nor am I an NVidia fan. I am, however, an Anandtech fan. And their decision to include the FTW edition card in this review means I can no longer come here and assume I'm reading something something unbiased and objective.
GeorgeH - Friday, October 22, 2010 - link
It was actually more of a shotgun blast aimed at the several silly posts implying AT was paid off by EVGA or Nvidia.If you've been reading AT for ~10 years, why would you assume that Ryan (or any other longtime contributor) suddenly decided to start bowing to outside pressure? If you stop lighting the torches and sharpening the pitchforks for half a second, you might realize that Ryan probably has a very good reason for including the OC card.
Even if I'm smoking crack WRT a GTX460+, what's the point of a review? It's not to give AMD and Nvidia a "fair" fight, it's to give us an idea of the best card to spend our money on - and if AMD or Nvidia get screwed in the process, I'm not going to be losing any sleep.
Typically, OC cards with a significant clock bump are fairly rare "Golden samples" and/or only provide marginal performance benefits without significantly increasing heat, noise, and power consumption. With the 460, Nvidia all but admitted they could've bumped the stock clocks quite significantly, but didn't want to threaten their other cards (*cough* 470 *cough*) if they didn't have to. This is reflected in what you can actually buy at Newegg - of the ~30 1GB 460's, only ~5 are running stock. 850MHz is still high, but is also right in line with the average of what you can expect any 460 to get to, so I don't think it's too far out of place.
Repeating what I said above, including the OC card was unfair to AMD, but is highly relevant to me and my wallet. I couldn't care less if AMD (or Nvidia) get screwed by an AT review - I just want to know what's best for me, and this article delivers. If the tables were turned, I'm sure that Ryan would have no problem including an OC AMD card in a Nvidia review - because it isn't about being a shill, it's about informing me, the consumer.
SandmanWN - Friday, October 22, 2010 - link
What? Put the crack down... Really, if you are short on time to review a product and you steal time away from that objective just to review a specially delivered hand selected opponents card instead of completing your assignment then you've not exactly been genuine to your readers or in this case to AMD.If you have time to add in an overclocked card then you need to do the same with the review card, otherwise the OC'd cards need to wait another day.
I have no idea how you can claim some great influence on your wallet when you have no idea of the OC capabilities of the 6000 series. If you actually bought the 460 off this review then you are banking that the overclock will hold up against a unknown variable. That's not exactly relevant to anyone's wallet.
GeorgeH - Friday, October 22, 2010 - link
An OC'd 460 competes with the 6870, and the 6870 doesn't really overclock at all.Even overclocked, a 6850 isn't going to touch a 6870, unless you're going to well over 1GHz (which short of a miracle isn't going to happen.)
It was disappointing that the review wasn't fleshed out more, but I'd say what's missing isn't as relevant to my buying decisions as how well the plethora of OC'd 460s compare to the 6870.
Parhel - Saturday, October 23, 2010 - link
"the 6870 doesn't really overclock at all"What? You're talking out of your ass No review site has even attempted a serious overclock yet. It's not even possible, as far as I know, to modify the voltage yet! We have no way to gauge how these cards overclock, and won't for several weeks.
"850MHz is still high, but is also right in line with the average of what you can expect any 460 to get to"
Now you're sounding like the shill. 850Mhz is not a realistic number if we're talking about 24/7 stability with stock cooling. No way.
GeorgeH - Saturday, October 23, 2010 - link
850MHz unrealistic? Nvidia flat out admitted that most cards are capable of at least ~800MHz (no volt mods, no nothing) and reviews around the web have backed this up, showing low to mid 800's on most stock cards, at stock voltages, running stock cooling. If you're worried about reliability, grab one of the many cards that come factory OC'd with a warranty.The 6870 doesn't now and never will overclock much at all, at least not in the way the 460 does. As with any chip, there will be golden sample cards that will go higher with voltage tweaks and extra cooling, but AMD absolutely did not leave ~20-25% of the 6870's average clockspeed potential on the table. The early OC reviews back this up as well, showing the 6870 as having minimal OC'ing headroom at stock voltages.
If you're waiting to compare the maximum performance that you can stretch out of a cherry-picked 6870 with careful volt mods and aftermarket cooling, you're going to be comparing it with a 460 @ ~950MHz, not ~850MHz.
As a guess, I'd say that your ignorance of these items is what led you to be so outraged at the inclusion of the OC 460 in the review. The magnitude of the OC potential of the 460 is highly atypical (at least in mid-range to high end cards), which is why I and many other posters have no issue with its similarly atypical inclusion in the review.