GeForce GTX260+ vs Radeon 4850 Part 2: Image Quality
Combined Mode Anti-Aliasing (xS)
As noted in part 1 of this article, the combined AA modes are available exclusively to nVidia cards, and their notable advantage is the ability to offer full screen super-sampling. Aside from stacking with anisotropic filtering, they deliver excellent image quality as they anti-alias both regular textures and shaders, something regular multi-sampling can’t do. TrAA/AAA is restricted to alpha textures, so regular textures require super-sampling in order to improve their look.
Here are the sample patterns for 8xS and 16xS, the two combined modes I’ll be covering today:
You can see eight and sixteen blue dots but more importantly, remember the single green dot that both 8xMSAA modes had earlier? That’s because multi-sampling only takes one texture (and shader) sample. Not so with super-sampling, and you can see two and four green dots with 8xS and 16xS respectively, lined up in an ordered grid. These samples will anti-alias everything, including all textures and shaders.
I’ve picked Doom 3 again and focused on a metallic floor. It exhibits texture aliasing and also shader aliasing (generated from the lighting shader). A strong anisotropic filter will help, but to really improve image quality in this situation, you need super-sampling.
260+ (4xAA)
260+ (8xS)
260+ (16xS)
You can clearly see both 8xS and 16xS impacting the pattern on the metallic floor, making the lines and lighting look smoother and more consistent. Note the extra improvement with the edges of the thick vertical lines that 16xS brings over 8xS. During in-game movement the floor will shimmer less when using xS modes compared to regular MSAA/CSAA/CFAA (edge) modes, because none of the latter modes have any effect on the texture whatsoever.
Since only nVidia offers full screen super-sampling on single card configurations, they are uncontested in this area. Older titles that are fast enough to use them have superb image quality. I really think ATi should offer them, at least unofficially. I can’t imagine it would be extraordinarily difficult to implement ordered grid super-sampling in the driver, and many ATi users have been asking for it for years.
Super-sampling can cause marginal blurring to 3D scenes in rare situations, but most of the time it’s only visible under a very heavy zoom from my testing. As a result, the readily visible in-game improvements more than outweigh this potential problem.
This is the best image quality comparison I’ve seen regarding the 4800s and GTX 200s. As always, great job BFG, and thanks for all of the hard work.
Damn, i have to agree. i was lucky to get a preview of this review and i learned a lot from it. BFG10K has been working on and polishing this review for quite some time and his hard work and effort really shows in a deep but very clearly understandable article. He does not waste a single word yet covers what he intends expertly.
Thanks for your support everyone. It’s the readers like you that make it all worthwhile.
I Used to be a die hard nvidia fan – loved my BFG 7950GT,Had a truly fabulous Zotac 8800GT AMP, But my last graphics upgrade has been my first to cross over to ATI and the HD4850. I now have 2 in crossfire (mainly because nvidia motherboards are quite frankly terrible ! Having been unfortunate enough to own a couple i include the Striker 2 extreme in that). I have friends still scared to try anything but NVIDIA or Infact made by BFG -(Great cards,incredible warranty – but have you ever had a gfx card for more than a couple of years ?)- They own 260’s and 280’s but i wouldn’t swap the ATI’s because the gaming performance and picture quality is i’m afraid to dissapoint you – BETTER WITH ATI 4800 SERIES GRAPHICS CARDS. These things happen AMD were great and overclocked for england ,Intel topped them with the core 2’s, Nvidia 8 series were great, GTX200 series came out too expensive and ATI struck gold with the RV770 chipset , swings and roundabouts gentlemen , What counts above all else is FPS per £/$ and that means ATI 4800 .
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