AMD's Radeon HD 5870: Bringing About the Next Generation Of GPUs
by Ryan Smith on September 23, 2009 9:00 AM EST- Posted in
- GPUs
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.
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BoFox - Friday, November 6, 2009 - link
Yep, that's turning up LOD to -1 or -2 depending on which game. It was done in Crysis, and with LOD at -2, it looked sharp with SSAA.The Wasrad - Wednesday, September 23, 2009 - link
Why are you using 4 gigs of ram with a 920?Do you understand how DDR3 memory works?
Ryan Smith - Wednesday, September 23, 2009 - link
Error when writing the chart. It has been corrected.Sc4freak - Wednesday, September 23, 2009 - link
Do you? The fact that the i7 920 works best in a triple-channel configuration has nothing to do with the fact that it uses DDR3.chizow - Wednesday, September 23, 2009 - link
Agreed and to add to that, the fact the third channel means very little when it comes to actual gaming performance makes it even less signficant. As compared to Lynnfield clock for clock, which is only dual channel:http://www.anandtech.com/cpuchipsets/showdoc.aspx?...">http://www.anandtech.com/cpuchipsets/showdoc.aspx?...
Von Matrices - Wednesday, September 23, 2009 - link
Could someone enlighten me as to why the 4870 X2 could be faster than the 5870 in some situations? It was noted it the article but never really explained. They have the same number of SP's, and one would expect crossfire scaling to be detrimental to the 4870 X2"s performance. Would this be indicative of the 5870 being starved for memory bandwidth in these situations or something else?Dobs - Wednesday, September 23, 2009 - link
4870x2 has 2Gb of DDR55870 only has 1 until the 2Gb edition comes out :)
nafhan - Wednesday, September 23, 2009 - link
Doesn't using dual GPU's effectively halve the onboard memory, as significant portions of the textures, etc. need to be duplicated? So, the 4870x2 has a memory disadvantage by requiring 2x memory to accomplish the same thing.chizow - Wednesday, September 23, 2009 - link
Right, with an X2 each GPU has a copy of the same frame buffer, so the total memory onboard is effectively halved. A 2GB frame buffer with 2 GPU is two of the same 1GB frame buffer mirrored on each.With the 5870 essentially being 2xRV790 on one chip, in order to accomplish the same frame rates on the same sized 1GB frame buffer, you would expect to need additional bandwidth to facilitate the transfers to and from the frame buffer and GPU.
chizow - Wednesday, September 23, 2009 - link
Ya he mentions bandwidth being a potential issue preventing the 5870 from mirroring the 4870X2's results.It could also be that the 5870's scheduler/dispatch processor aren't as efficient at extracting performance as driver forced AFR. Seems pretty incredible, seeing as physically doubling GPU transistors on a single die has always been traditionally better than multi-GPU scaling.
Similarly, it could be a CPU limitation where CF/SLI benefit more from multi-threaded driver performance, whereas a single GPU would be limited to a single fast thread or core's performance. We saw this a bit as well last year with the GT200s compared to G92s in SLI.