GeForce GTX260+ vs Radeon 4850 Part 2: Image Quality
Pure Edge Anti-Aliasing
As I explained earlier, super-sampling can cause marginal blurring and some are opposed to it on this basis, and they demand stronger pure edge AA instead. So this next section will test AA modes that do just that.
16xQ is nVidia’s strongest pure edge AA mode, combining 8xMSAA with 8xCSAA. The other 16xAA mode (4xMSAA + 12 CSAA) is generally inferior to 8xMSAA, so I won’t bother looking at it today.
ATi’s enhanced edge modes are 12xAA (4xMSAA + edge detect) and 24xAA (8xMSAA + edge detect). These CFAA modes are like narrow/wide tent in that they use adjacent pixels for additional samples, but the shader detects polygon edges and only anti-aliases those situations, hence avoiding the internal blurring that narrow/wide tent cause. Edge detect modes don’t render the scene higher than the output, hence saving memory bandwidth and storage compared to traditional AA methods.
Here are some zoomed images of a crane in Half-Life 2:
4850 (12xAA)
4850 (24xAA)
260+ (16xQ)
The red arrows in the 12x image illustrate the three sections of interest.
16xQ is slightly smoother than 12xAA along most of the crane’s main support beams, areas like (1).
16xQ and 24xAA are tremendously close, and the differences at this level of edge AA probably become academic in this particular scene. Nevertheless, 24xAA has a slight advantage with the power line (2) and the thin rails (3).
It’s worth noting that while 16xQ can approach 16xMSAA in terms of quality, it can lose effectiveness in some situations due to its coverage sampling component not being completely robust. Some examples include polygons sharing the same edges, or stencil shadows. In those situations the image quality of 16xQ will be closer to 8xMSAA, but 24xAA will be free from such limitations and should deliver more consistent results.
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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