ATI's Late Response to G70 - Radeon X1800, X1600 and X1300
by Derek Wilson on October 5, 2005 11:05 AM EST- Posted in
- GPUs
Adaptive AA
Antialiasing is becoming more and more important as graphics cards get faster. With the 7800 GTX (and the X1800 XT when it comes along), there are very few monitors that can really stress the fill rate potential of these cards. Not everyone has 30" Apple Cinema Displays, and even at resolutions of 1600x1200 we see CPU limitedness start to become a factor. With many 1600x1200 flat panels out there on the market, this "monitor limitedness" will only get worse and worse as graphics cards continue to improve at a significantly faster rate than display technology. Quality enhancing features will get more and more attention in the meantime, and more power can be spent on enhancing a game rather than just rendering it. Thus more focus has recently been put into antialiasing algorithms.
Multisample AA (MSAA) has been the predominant method of antialiasing for quite a few years now, but it is not perfect. MSAA only works around polygon edges by smoothing lines when the area covered by one pixel falls over multiple triangles. SSAA oversamples everything at every pixel and is traditionally implemented by rendering a scene at a larger resolution and then down-sampling the image to fit the display. Lots of power is wasted with SSAA in areas that are covered by the same color, so MSAA wins out in performance while sacrificing a bit of quality.
One of the major down sides of MSAA is its inability to antialias the interior of polygons mapped with a texture that includes transparency. Things like wires, fences, and foliage are often rendered with huge triangles and transparent texture maps. Since MSAA only works on polygon edges, the areas between transparent and opaque parts inside these large polygons can look very jagged. The only way to combat this is to take multiple texture samples per pixel within the same polygon. This can be done by performing multiple texture lookups per pixel rather than simply rendering the scene at a huge resolution.
ATI is including a feature called Adaptive Antialiasing in the Catalyst release that comes along with the X1000 series. Adaptive AA is functionally similar to NVIDIA's Transparency AA. Rather than just doing multi-sample (MSAA), ATI is able to adaptively take multiple texture samples per pixel in areas that would benefit from including additional texture samples (essentially resulting in a combination of MSAA and SSAA where needed). Depending on where ATI determines it is necessary to perform multiple texture samples, poorly designed or easily aliased textures can benefit in addition to those that include transparency.
Unlike NVIDIA's Transparency AA, ATI's Adaptive AA will be available to all ATI hardware owners. How's that for value-add! This could be a very nice thing for X800/X850 series owners stuck with 1280x1024 panels. Apparently ATI has been tweaking this technology for a few years now, but held off on its introduction until this launch. The use of this feature on most older hardware won't be widespread as performance will degrade too much. In these cases, increasing resolution is almost always more effective than increasing AA quality. Here's a look at the Adaptive AA as compared to Transparency AA:
Continuing down the path to high quality AA, ATI has improved the sub-pixel accuracy of their antialiasing hardware. Rather than being limited to selecting samples on an 8x8 grid, ATI is now able to work with select samples from a 16x16 grid. Moving up from 64 to 256 potential sub-pixels per pixel, ATI has improved the accuracy of their AA algorithm. This accuracy improvement may not be directly noticeable, but this enhancement will also improve the quality of dense AA methods like CrossFire's SuperAA technology. Workstation users will also benefit as this will likely translate to improved point and line antialiasing quality.
The one thing I would ask for from ATI is the ability to turn off "gamma-correct" AA. Such methods only shift inaccuracies between overly dark and overly bright pixels. Consistent results would only be possible if all displays were the same. Since they are not, it's really a six of one half-dozen of the other choice. Putting the decision in the user's hands as to what looks better is always our favored suggestion.
As if all of these enhancements weren't enough to top off ATI's already industry leading antialiasing (NVIDIA's grid aligned sample patterns just can't touch ATI's fully programmable sample patterns in quality), ATI has also vastly improved antialiasing performance with the X1000 generation of hardware. Neither NVIDIA nor previous generation ATI hardware can match the minimal performance hit the X1000 series incurs when enabling standard AA. The performance we see is likely due to a combination of the improvements made to the AA hardware itself along side enhancements to the memory architecture that allow for higher bandwidth and the prioritization of data moving on the ring bus.
Antialiasing is becoming more and more important as graphics cards get faster. With the 7800 GTX (and the X1800 XT when it comes along), there are very few monitors that can really stress the fill rate potential of these cards. Not everyone has 30" Apple Cinema Displays, and even at resolutions of 1600x1200 we see CPU limitedness start to become a factor. With many 1600x1200 flat panels out there on the market, this "monitor limitedness" will only get worse and worse as graphics cards continue to improve at a significantly faster rate than display technology. Quality enhancing features will get more and more attention in the meantime, and more power can be spent on enhancing a game rather than just rendering it. Thus more focus has recently been put into antialiasing algorithms.
Multisample AA (MSAA) has been the predominant method of antialiasing for quite a few years now, but it is not perfect. MSAA only works around polygon edges by smoothing lines when the area covered by one pixel falls over multiple triangles. SSAA oversamples everything at every pixel and is traditionally implemented by rendering a scene at a larger resolution and then down-sampling the image to fit the display. Lots of power is wasted with SSAA in areas that are covered by the same color, so MSAA wins out in performance while sacrificing a bit of quality.
One of the major down sides of MSAA is its inability to antialias the interior of polygons mapped with a texture that includes transparency. Things like wires, fences, and foliage are often rendered with huge triangles and transparent texture maps. Since MSAA only works on polygon edges, the areas between transparent and opaque parts inside these large polygons can look very jagged. The only way to combat this is to take multiple texture samples per pixel within the same polygon. This can be done by performing multiple texture lookups per pixel rather than simply rendering the scene at a huge resolution.
ATI is including a feature called Adaptive Antialiasing in the Catalyst release that comes along with the X1000 series. Adaptive AA is functionally similar to NVIDIA's Transparency AA. Rather than just doing multi-sample (MSAA), ATI is able to adaptively take multiple texture samples per pixel in areas that would benefit from including additional texture samples (essentially resulting in a combination of MSAA and SSAA where needed). Depending on where ATI determines it is necessary to perform multiple texture samples, poorly designed or easily aliased textures can benefit in addition to those that include transparency.
Unlike NVIDIA's Transparency AA, ATI's Adaptive AA will be available to all ATI hardware owners. How's that for value-add! This could be a very nice thing for X800/X850 series owners stuck with 1280x1024 panels. Apparently ATI has been tweaking this technology for a few years now, but held off on its introduction until this launch. The use of this feature on most older hardware won't be widespread as performance will degrade too much. In these cases, increasing resolution is almost always more effective than increasing AA quality. Here's a look at the Adaptive AA as compared to Transparency AA:
NVIDIA 7800 GTX 4xAA
NVIDIA 7800 GTX 4xAA
Mouse over to cycle images
Continuing down the path to high quality AA, ATI has improved the sub-pixel accuracy of their antialiasing hardware. Rather than being limited to selecting samples on an 8x8 grid, ATI is now able to work with select samples from a 16x16 grid. Moving up from 64 to 256 potential sub-pixels per pixel, ATI has improved the accuracy of their AA algorithm. This accuracy improvement may not be directly noticeable, but this enhancement will also improve the quality of dense AA methods like CrossFire's SuperAA technology. Workstation users will also benefit as this will likely translate to improved point and line antialiasing quality.
The one thing I would ask for from ATI is the ability to turn off "gamma-correct" AA. Such methods only shift inaccuracies between overly dark and overly bright pixels. Consistent results would only be possible if all displays were the same. Since they are not, it's really a six of one half-dozen of the other choice. Putting the decision in the user's hands as to what looks better is always our favored suggestion.
As if all of these enhancements weren't enough to top off ATI's already industry leading antialiasing (NVIDIA's grid aligned sample patterns just can't touch ATI's fully programmable sample patterns in quality), ATI has also vastly improved antialiasing performance with the X1000 generation of hardware. Neither NVIDIA nor previous generation ATI hardware can match the minimal performance hit the X1000 series incurs when enabling standard AA. The performance we see is likely due to a combination of the improvements made to the AA hardware itself along side enhancements to the memory architecture that allow for higher bandwidth and the prioritization of data moving on the ring bus.
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HamburgerBoy - Wednesday, October 5, 2005 - link
Seems kind of odd that you'd include nVidia's best but not ATi's.cryptonomicon - Wednesday, October 5, 2005 - link
I was expecting ATI to make a comback here, but the performance is absolutely abysmal in most games. I dont know what else to say except this product is just gonna be sitting in shelves unless the price is cut severely.bob661 - Thursday, October 6, 2005 - link
LOL! I wouldn't say abysmal. Abysmal would be the X1800XT performing like a 6600GT. The card that doesn't do well is the X1600. X1800's are fantastic performers and certainly much better than my 6600GT at displaying all of a games glory. It just wasn't the ass kicker most everyone hyped it up to be. But technically speaking, it IS an ass kicker.flexy - Wednesday, October 5, 2005 - link
i am a bit disappointed - while at work i overflew the other reviews and then, as the crowning end of my day i read the AT review.I (and probably many others) were waiting for this card like it's the best think since sliced bread - and now, WAY too late we do *indeed* have a good card - but a card which is a contender to NV's offerings and nothing groundbreaking.
Don't get me wrong - better AF/AA is something i always have a big eye on, but then ATI always had this slight edge when it came to AF/AA.
The pure performance in FPS itself is rather sobering - just what we're used to the last few years...usually we have TWO high-end cards out which are PRETT MUCH comparable - and no card is really the "sliced bread" thing which shadows all others.
This is kind of sad.
The price also plays a HUGE factor - and amongst the nice AA/AF features i have a hard time to legitimate say spending $500 for "this edge"...especially as someone who already owns a X850XT .
Not as long i am still playable in HL2/DOD/Lost Coats etc....i dont think i will see FPS fall *that quick* - in other words: I can "afford" to wait longer (R580 ?) and wait for appropriate Game engines (UT2K4 ??) which would make it necessary for me to ditch my X850XT because the X850 got "slow".
D3/OpenGL performance is still disappointing - but then i dont know what NV-specific code D3 uses - but still sad to see this card getting it in the face even if it now has SM3.0 and everything.
Availability:
Well..here we go again....
Bottomline: If i were rich and the card would be orderable RIGHT NOW i would get the XT - no question.
But since i am not rich and the card is *a bit* a disappointment and obviously NOT EVEN AVAILABLE - i will NOT get this card.
It's time to sit back, relax, enjoy my current hardware, watch the prices fall, watch the drivers get better...and then, maybe, one day get one of those or A R580 :)
I WISHED it would NOT have been a day making one "sit and relax" but instead burst out in joy and enthusiasm....but well, then this is real life :)
Wesleyrpg - Thursday, October 6, 2005 - link
summarised very well mate!Regs - Wednesday, October 5, 2005 - link
They were likely better off trying to market that we didn't need new video cards this year and save their capital for next year. These performance charts, especially the "mid range" parts are awfully embarrassing to their company.photoguy99 - Wednesday, October 5, 2005 - link
I assume it was not one of the cards that come overclocked stock to 490Mhz?It seems like it would be fair to use a 490Mhz NVidia part since manufacturers are selling them at that speed out of the box with full warrenty intact.
Evan Lieb - Wednesday, October 5, 2005 - link
"Unless you want image quality."There is no image quality difference, and I doubt you've used either card. Fact of the matter is that you'll never notice IQ differences in the vast majority of the games today. Hell, it's even hard to notice differences in slower paced games like Splinter Cell. The reality is that speed is and always will be the number one priority, because eye candy doesn't matter if you're bogged down by choppy frame rate.
Right now, there is zero reason to want to purchase these cards, if you can even find them. That's fact. Accept it and move on until something else is released.
Madellga - Thursday, October 6, 2005 - link
Quality includes also playing a game without shimmering. I can't get that on my 7800GTX.Before anyone replies, the 78.03 drivers improve a lot the problem but does not fix it.
The explanation is inside Derek's article:
"Starting with Area Anisotropic (or high quality AF as it is called in the driver), ATI has finally brought viewing angle independent anisotropic filtering to their hardware. NVIDIA introduced this feature back in the GeForce FX days, but everyone was so caught up in the FX series' abysmal performance that not many paid attention to the fact that the FX series had better quality anisotropic filtering than anything from ATI. Yes, the performance impact was larger, but NVIDIA hardware was differentiating the Euclidean distance calculation sqrt(x^2 + y^2 + z^2) in its anisotropic filtering algorithm. Current methods (NVIDIA stopped doing the quality way) simply differentiate an approximated distance in the form of (ax + by + cz). Math buffs will realize that the differential for this approximated distance simply involves constants while the partials for Euclidean distance are less trivial. Calculating a square root is a complex task, even in hardware, which explains the lower performance of the "quality AF" equation.
Angle dependant anisotropic methods produce fine results in games with flat floors and walls, as these textures are aligned on axes that are correctly filtered. Games that allow a broader freedom of motion (such as flying/space games or top down view games like the sims) don't benefit any more from anisotropic filtering than trilinear filtering. Rotating a surface with angle dependant anisotropic filtering applied can cause noticeable and distracting flicker or texture aliasing. Thus, angle independent techniques (such as ATI's area aniso) are welcome additions to the playing field. As NVIDIA previously employed a high quality anisotropic algorithm, we hope that the introduction of this anisotropic algorithm from ATI will prompt NVIDIA to include such a feature in future hardware as well. "
Phantronius - Wednesday, October 5, 2005 - link
Unless you a fanboy