Angle-Independent Anisotropic Filtering At Last

For a number of years now the quality of anisotropic filtering has been slowly improving. Early implementations from AMD and NVIDIA were highly angle-dependent, resulting in a limited improvement to image quality from such filtering. The angle-dependent nature lead to shimmering and other artifacting that was not ideal.

As of the previous generation of cards, the quality of anisotropic filtering had become pretty good. NVIDIA’s best filtering mode was pretty close to angle-independent, and AMD’s only slightly worse. Neither was perfect, but neither was bad either.


The Radeon HD 4890


The GeForce GTX 285

However so long as no one had an angle-independent implementation, there was room to improve. And AMD has gone there. The anisotropic filtering algorithm used by the 5000 series is now truly and completely angle-independent. There are no more filtering tricks being used.


The Radeon HD 5870: Perfection

As you can see, the MIP maps in our venerable D3D AF Tester are perfectly circular, the hallmark of an angle-independent implementation. With angle-independent filtering, this effectively marks the end of the filtering arms race. AMD has won, and should NVIDIA catch up in the future the two would merely be tied. There’s nowhere left to go for quality beyond angle-independent filtering at the moment.

AMD tells us that there is no performance hit with their new algorithm compared to their old one. This is a bit hard to test since we can’t enable the old algorithm on the 5870, but certainly whatever performance hit there is, is similarly minor. In all of the testing we’re doing today, you will see results done with 16x anisotropic filtering used.

What you won’t see however is a difference, particularly with our static screenshots. When discussing the matter, AMD noted that the difference in perceived quality between the old algorithm and the new one was practically the same. After looking at matters we find ourselves in agreement with AMD; we were not able to come up with any situations where there was a noticeable difference, beyond the obvious AF quality tests that are designed to identify such changes.

Regardless of the outcome, AMD deserves kudos for making angle-independent anisotropic filtering happen. It’s demonstrably perfect filtering with no speed hit versus the previous generation of filtering; making it in essence a “free” improvement in image quality, however slight the real-world results are. We’re always ready to get better image quality out of our video cards, after all.

More GDDR5 Technologies: Memory Error Detection & Temperature Compensation The Return of Supersample AA
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  • mapesdhs - Saturday, September 26, 2009 - link


    MODel3 writes:
    > 1.Geometry/vertex performance issues ...
    > 2.Geometry/vertex shading performance issues ...

    Would perhaps some of the subtests in 3DMark06 be able to test this?
    (not sure about Vantage, never used that yet) Though given what Jarred
    said about the bandwidth and other differences, I suppose it's possible
    to observe large differences in synthetic tests which are not the real
    cause of a performance disparity.

    The trouble with heavy GE tests is, they often end up loading the fill
    rates anyway. I've run into this problem with the SGI tests I've done
    over the years:

    http://www.sgidepot.co.uk/sgi.html">http://www.sgidepot.co.uk/sgi.html

    The larger landscape models used in the Inventor tests are a good
    example. The points models worked better in this regard for testing
    GE speed (stars3/star4), but I don't know to what extent modern PC
    gfx is designed to handle points modelling - probably works better
    on pro cards. Actually, Inventor wasn't a good choice anyway as it's
    badly CPU-bound and API-heavy (I should have used Performer, gives
    results 5 to 10X faster).

    Anyway, point is, synthetic tests might allow one to infer that one
    aspect of the gfx pipeline is a bottleneck when infact it isn't.

    Ages ago I emailed NVIDIA (Ujesh, who I used to know many moons ago,
    but alas he didn't reply) asking when, if ever, they would add
    performance counters and other feedback monitors to their gfx
    products so that applications could tell what was going on in the
    gfx pipeline. SGI did this ages years ago, which allowed systems like
    IR to support impressive functions such as Dynamic Video Resizing by
    being able to monitor frame by frame what was going on within the gfx
    engine at each stage. Try loading any 3D model into perfly, press F1
    and click on 'Gfx' in the panel (Linux systems can run Performer), eg.:

    http://www.sgidepot.co.uk/misc/perfly.gif">http://www.sgidepot.co.uk/misc/perfly.gif

    Given how complex modern PC gfx has become, it's always been a
    mystery to me why such functions haven't been included long ago.
    Indeed, for all that Crysis looks amazing, I was never that keen on
    it being used as a benchmark since there was no way of knowing
    whether the performance hammering it created was due to a genuinely
    complex environment or just an inefficient gfx engine. There's still
    no way to be sure.

    If we knew what was happening inside the gfx system, we could easily
    work out why performance differences for different apps/games crop
    up the way they do. And I would have thought that feedback monitors
    within the gfx pipe would be even more useful to those using
    professional applications, just as it was for coders working on SGI
    hardware in years past.

    Come to think of it, how do NVIDIA/ATI even design these things
    without being able to monitor what's going on? Jarred, have you ever
    asked either company about this?

    Ian.

    Reply
  • JarredWalton - Saturday, September 26, 2009 - link

    I haven't personally, since I'm not really the GPU reviewer here. I'd assume most of their design comes from modeling what's happening, and with knowledge of their architecture they probably have utilities that help them debug stuff and figure out where stalls and bottlenecks are occurring. Or maybe they don't? I figure we don't really have this sort of detail for CPUs either, because we have tools that know the pipeline and architecture and they can model how the software performs without any hardware feedback. Reply
  • MODEL3 - Thursday, October 1, 2009 - link

    I checked the web for synthetic geometry tests.
    Sadly i only found 3dMark Vantage tests.
    You can't tell much from them, but they are indicative.

    Check:

    http://www.pcper.com/article.php?aid=783&type=...">http://www.pcper.com/article.php?aid=783&type=...

    GPU Cloth: 5870 is only 1,2X faster than 4890. (vertex/geometry shading test)
    GPU Particles: 5870 is only 1,2X faster than 4890. (vertex/geometry shading test)

    Perlin Noise: 5870 is 2,5X faster than 4890. (Math-heavy Pixel Shader test)
    Parallax Occlusion Mapping: 5870 is 2,1X faster than 4890. (Complex Pixel Shader test)

    All the above 4 tests are not bandwidth limited at all.
    Just for example, if you check:

    http://www.pcper.com/article.php?aid=674&type=...">http://www.pcper.com/article.php?aid=674&type=...

    You will see that a 750MHz 4870 512MB is 20-23% faster than a 625MHz 4850 in all the above 4 tests, so the extra bandwidth (115,2GB/s vs 64GB/s) it doesn't help at all.
    But 4850 is extremely bandwidth limited in the color fillrate test (4870 is 60% faster than 4850)

    Also it shouldn't be a problem of the dual rasterizer/dual SIMDs engine efficiency since synthetic Pixel Shader tests is fine (more than 2X) while the synthetic geometry shading tests is only 1,2X.

    My guess is ATI didn't improve the classic geometry set-up engine and the GS because they want to promote vertex/geometry techniques based on the DX11 tesselator from now on.
    Reply
  • Zool - Friday, September 25, 2009 - link

    In Dx11 the fixed tesselation units will do much finer geometry details for much less memmory space and on chip so i think there isnt a single problem with that. Also the compute shader need minimal memory bandwith and can utilize plenty of idle shaders. The card is designed with dx11 in mind and it isnt using the wholle pipeline after all. I wouldnt make too early conclusions.(I think the perfomance will be much better after few drivers)

    Reply
  • MODEL3 - Saturday, September 26, 2009 - link

    The DX11 tesselator in order to be utilized must the game engine to take advantage of it.
    I am not talking about the tesselator.
    I am talking about the classic Geometry unit (DX9/DX10 engines) and the Geometry Shader [GS] (DX10 engines only).

    I'll check to see if i can find a tech site that has synthetic bench for Geometry related perf. and i will post again tomorrow, if i can find anything.

    Reply
  • JarredWalton - Friday, September 25, 2009 - link

    It's worth noting that when you factor in clock speeds, compared to the 5870 the 4870X2 offers 88% of the core performance and 50% more bandwidth. Some algorithms/games require more bandwidth and others need more core performance, but it's usually a combination of the two. The X2 also has CrossFire inefficiencies to deal with.

    More interesting perhaps is that the GTX 295 offers (by my estimates, which admittedly are off in some areas) roughly 10% more GPU shader performance, about 18.5% more fill rate, and 46% more bandwidth than the HD 5870. The fact that the HD 4870 is still competitive is a good sign that ATI is getting good use of their 5 SPs per Stream Processor design, and that they are not memory bandwidth limited -- at least not entirely.
    Reply
  • SiliconDoc - Wednesday, September 30, 2009 - link

    The 4870x2 has somewhere around "double the data paths" in and out of it's 2 cpu's. So what you have with the 5870 putting as some have characterized " 2x 770 cores melded into one " is DOUBLE THE BOTTLENECK in and out of the core.
    They tried to compensate with ddr5 1200/4800 - but the fact remains, they only get so much with that "NOT ENOUGH DATA PATHS/PINS in and out of that gpu core."
    Reply
  • cactusdog - Friday, September 25, 2009 - link

    Omg these cards look great. Lol Silicon Doc is so gutted and furious he is making hmself look like a dam fool again only this time he should be on suicide watch...Nvidia cards are now obsolete..LOL. Reply
  • mapesdhs - Friday, September 25, 2009 - link


    Hehe, indeed. Have you ever seen a scifi series called, "They Came
    From Somewhere Else?" S.D.'s getting so worked up, reminds me of
    the scene where the guy's head explodes. :D

    Hmm, that's an alternative approach I suppose in place of post
    moderation. Just get someone so worked up about something they'll
    have an aneurism and pop their clogs... in which case, I'll hand
    it back to Jarred. *grin*

    Ian.

    Reply
  • SiliconDoc - Friday, September 25, 2009 - link

    That is quite all right, you fellas make sure to read it all, I am more than happy that the truth is sinking into your gourds, you won't be able to shake it.
    I am very happy about it.
    Reply

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