NVIDIA's GeForce 8800 (G80): GPUs Re-architected for DirectX 10
by Anand Lal Shimpi & Derek Wilson on November 8, 2006 6:01 PM EST- Posted in
- GPUs
What's Transparency AA?
Transparency AA is NVIDIA's method of applying AA to transparent textures. Because MSAA only looks at one texture sample per pixel per polygon where more than one polygon slices a pixel area, it is not able to smooth jagged edges in transparent textures. In order to combat this, NVIDIA applies supersample AA to transparent textures. Their multisample transparency AA really doesn't do much for visual quality, so we will be ignoring it today. It only allows multisample through transparent texture areas and not of the texture itself.
Supersample AA performs a texture lookup at each sub-pixel to determine how much of the pixel falls on a transparent area of the texture and how much falls on an opaque area. The analog in ATI hardware is called Adaptive AA, which does basically the same thing. This generally has a very large performance impact for 3D scenes with many transparent textures (fence, bushes, leaves, and the like).
All screenshots on this page are 400% zooms of the highlighted portion of the following Half Life 2 screenshot:
Here's a look at Half-Life 2 with and without Transparency AA. We can clearly see how the leaves of the trees get smoothed out and look much better.
G80 No Transparency G80 Transparency AA
Hold mouse over links to see Image Quality
When comparing G70, G80, and R580, we have to remember that for NVIDIA hardware we've disabled gamma correct AA. It isn't possible to do this on ATI hardware, and thus we have a comparison of gamma correct AA on transparent textures as well.
G70 4X No Gamma G80 4X No Gamma ATI 4X Gamma
Hold mouse over links to see Image Quality
G70 and G80 don't look that different, but the R580 creates a kind of mushy look around the trees. This is another side effect of gamma correct AA and its potential negative impact on image quality. Worse examples include wire mesh or fences built with transparent textures: gamma correct AA can end up making parts of a fence disappear. Ideally, if we could apply gamma correct AA to high contrast edges and disable it for everything else, we'd see an image quality improvement. But the downsides just keep piling up with thin lines and transparent textures causing problems for gamma correction.
While transparency AA does enhance image quality a good deal, we do need to consider the performance impact. We'll revisit our antialiasing scaling graph from our CSAA page with Transparency and Adaptive AA enabled.
With G80, we see great performance at high resolution with high levels of AA while Transparency AA is enabled. With this level of performance, as long as R600 is able to keep up, we would love to check the Transparency AA check box every time we test with AA. For now, the performance degradation in R580 is just too high to justify at resolutions over 1600x1200 in most cases. An increase in resolution to a comparable performance level will net a higher gain in image quality.
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aweigh - Friday, November 10, 2006 - link
You can just use the program DX Tweaker to enable Triple Buffering in any D3D game and use your VSYNC with negligable performance impact. So you can play with your VSYNC, a high-res and AA as well. :)aweigh - Friday, November 10, 2006 - link
I'm gonna buy an 88 specifically to use 4x4 SuperSampling in games. Why bother with MSAA with a card like that?DerekWilson - Friday, November 10, 2006 - link
Supersampling can make textures blurry -- especially very detailed textures.And the impact will be much greater with the use of longer more detailed pixel shaders (as the shaders must be evaluated at every sub-pixel in supersample).
I think transparency / adaptive AA are enough.
On your previous comment, I don't think we're to the point where we can hit triple buffering, vsync, high levels of AA AND high resolution (2560x1600) without some input lag (triple buffering plus vsync with framerates less than your refresh rate can cause problems).
If you're talking about enabling all these options on a lower resolution lcd panel, then I can definitely see that as a good use of the hardware. And it might be interesting to look at more numbers with these type of options enabled.
Thanks for the suggestion.
aweigh - Saturday, November 11, 2006 - link
I never knew that about SuperSampling. Is it something similar to Quincux blurring? And would using a negative LOD via RivaTuner/nHancer counteract the effect?How about NVIDIA's Digital Sharpness setting in Color Correction? I've found a smidge of sharpening can do wonders to improve overall clarity.
By the way, when you said Adaptive AA, were you referring to ATI cards?
Unam - Friday, November 10, 2006 - link
Derek,Saw your comment regarding the rationale for the test resolution, while I understand your reasoning now, it still begs the question how many of your readers have 30" LCD flat panels?
DerekWilson - Friday, November 10, 2006 - link
There might not be many out there right now, but it's still the right test platform for G80. We did test down to 1600x1200, so people do have information if they need it.But it speaks to who should own an 8800 GTX right now. It doesn't make sense to spend that much money on a part if you aren't going to get anything out of it with your 1280x1024 panel.
Owners of a 2560x1600 panel will want an 8800 GTX. Owners of an 8800 GTX will want a 2560x1600 panel. Smooth framerates with the ability to enable 4xAA in every game that allowed it is reason enough. People without a 2560x1600 panel should probably wait until prices come down on the 8800 GTX or until games that are able to push the 8800 GTX harder to buy the card.
Unam - Tuesday, November 14, 2006 - link
Derek,A follow up to testing resolutions, the FPS numbers we see in your articles, are they maximum, minimum or average?
Unam - Friday, November 10, 2006 - link
Who the heck runs 2560x1600? At 4XAA? Come on guys, real world benchmarks please!DerekWilson - Friday, November 10, 2006 - link
we did:1600x1200, 1920x1440, and even 1280x1024 in Oblivion
dragonsqrrl - Thursday, August 25, 2011 - link
....lol, owned.