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 Gamma Correct AA?
Gamma correction is a technique used to map linearly increasing brightness data to a display device in a way that conveys linearly increasing intensity. As displays are nonlinear devices, gamma correction requires a nonlinear adjustment to be made to brightness values before being sent to the display. Ideally, gamma corrected linear steps in the brightness of a pixel will result in linear steps in perceived intensity. The application in antialiasing is that high contrast edges can appear under aliased if the brightness of a pixel isn't adjusted high enough for humans to perceive an increase in intensity after being displayed by the monitor.
Unfortunately, gamma correcting AA isn't always desirable. Different CRT, LCD, and TVs have different gamma characteristics that make choosing one gamma correction scheme more or less effective per device. It can also result in brighter colored sub-samples having a heavier influence on the color of a pixel than darker sub-samples. This causes problems for thing like thin lines.
To illustrate the difference, we'll look at images of Half-Life taken on G80 with and without gamma correction enabled.
16XQ No Gamma 16XQ Gamma
Hold mouse over links to see Image Quality
16XQ No Gamma 16XQ Gamma
Hold mouse over links to see Image Quality
We can see the antenna decrease in clarity due to the fact that each of the brighter subsamples has a disproportionately higher weight than the darker subsamples. As far as the roof line is concerned, our options are to see the roof blurring out into the sky, or watching the sky cut into the roof.
Really, edge AA with and without gamma correction is six of one and half a dozen of the other. Combine this with the fact that the effect is different depending on the monitor being used and the degraded visibility of thin lines and we feel that gamma correct AA isn't a feature that improves image quality as much as it just changes it.
While we are happy that NVIDIA has given us the choice to enable or disable gamma correct AA as we see fit, with G80 the default state has changed to enabled. While this doesn't have an impact on performance, we prefer rendering without gamma correct AA enabled and will do so in our performance tests. We hope that ATI will add a feature to disable gamma correct AA in the future as well. For now, let's take a look at R580 and G80 compared with gamma correction enabled.
G80 4X Gamma ATI 4X Gamma
Hold mouse over links to see Image Quality
G80 4X Gamma ATI 4X Gamma
Hold mouse over links to see Image Quality
At 4xAA with gamma correction enabled, it looks like ATI is able to produce a better quality image. Some of the wires and antenna on NVIDIA hardware area a little more ragged looking while ATI's images are smoothed better.
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DerekWilson - Thursday, November 9, 2006 - link
i'm sure there was a lot burried in there ... sorry if it wasn't easy to find.8800 gtx and gtx are both no louder than 7900 gtx. 1950 xtx still takes the cake for loudest graphics card around by a long shot -- especially after it heats up in a game.
crystal clear - Thursday, November 9, 2006 - link
My comments in Daily Tech on this subject-More "G80" Derivatives in February R
E: More info would be nice
By crystal clear on 11/8/06, Rating: 2
By crystal clear on 11/8/2006 8:03:43 AM , Rating: 2
If you link VISTA -SANTA ROSA platform-Core2DUO(merom)CPU line up(T7300,7500,7700 models)then a matching Graphics card
to complete the link.
So a G80 for laptops/notebooks?
The pairing of Intels Santa Rosa platform with Vista in the 2Q 07 is next big thing for the first tier notebook manufacturers & all they need is a matching G80 for this setup.
Unquote-
Nvidia currently caters to Desktop requirement/needs with the new G80 releases,wonder how the notebook/server versions will be-with Vista ofcourse.
yyrkoon - Thursday, November 9, 2006 - link
Vitual memory is probably a good thing for most cases, but in the graphics arena, this *could* potentially make for sloppy/ bad coding practises. Knowing a lot of game devers (some of which actually work for well known companies), I've heard them from time to time complain about maxing a 16x PCI-E pipe. What I'm trying to say here, is that while it would be a good thing for never having to run out of texture memory, but that system memory, and definately the swap disk can not hold a candle to the memory bandwidth that most Video cards are capable of. End result, is that you definately *will* get a performance hit. All this, and we already know the memory bandwidth capabilities of modern PCs, suffice it to say, the most we'll see from current systems is what ? 12-13K GB/s ? Even a 7800GS can do roughly 35 GB/s on card. A 7600GT ? 22GB/s ?Still I think Directx10 is a very good thing, and as I didnt read the whole article, perhaps a missed a little ? Reason being, I've been reading about Directx10 since April, and a friend of mine was privy to some of this information after an interview with ATI.
http://www.gamedev.net/reference/programming/featu...">http://www.gamedev.net/reference/programming/featu...
saratoga - Thursday, November 9, 2006 - link
I don't know how they threading really works, but its quite possible VM support is required in order to allow multiple threads to run without stepping all over each other,.saratoga - Thursday, November 9, 2006 - link
Sorry, should read "I don't know how THEIR threading works"falc0ne - Thursday, November 9, 2006 - link
I don't know what is the problem but I'm really unable to see the images within the latest articles from Anand...Can anyone give me a suggestion? What might be the cause of that?The thing is I'm really, really interested in these articles and I need to see those images. Thanks
yyrkoon - Thursday, November 9, 2006 - link
Oh, er, then in the options tab of Firefox, (tools->options->content) check the "load images" check box ;)falc0ne - Thursday, November 9, 2006 - link
well...it would've been simple but I'm afraid is not that...It might be the addblock extension from firefox, other than that I have nooo ideeea...Well I will use the IE tab option instead and load the pages using IE 7. Thanks anyway:)yyrkoon - Thursday, November 9, 2006 - link
Checked the exceptions list ? I know that firefox makes it really simple to block images from a site (to a point of being too easy).JarredWalton - Thursday, November 9, 2006 - link
If you've got AdBlock on Firefox, press Ctrl+Shift+A and you can see what it's blocking. If it blocks the images.anandtech.com stuff, you can then see which RegEx isn't working right and edit that.