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Old 06-26-05, 02:47 AM   #1
ChrisRay
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Arrow GeForce 7800 GTX antialiasing investigation

Geforce 7800GTX Anti Aliasing Investigation




Introduction: Last year at the release of the Nv4x hardware. Nvidia implemented Rotated Grid Multisampling for its Nv4x hardware greatly improving quality of their 4x AA and beyond modes. I took it upon myself to write up an Nv4x AA Investigation where I covered the various sample patterns and hidden modes. Since the actual sampling positions for the old modes hasnt changed any. I decided it would be redundant to rehash the same material. Instead, I have decided to focus on the new modes available to the G70 owners. Namely, Transparent AA and Gamma Corrected Anti Aliasing.





Gamma Corrected: Essentially provides superior color reproduction. It can improve your subjective opinion of the image. It can have noticable effect on thin surfaces such power lines often found in games such as Call of Duty or Half Life 2. It is easily toggled off and on through the advanced options in the Nvidia control panel.




Transparency Anti Aliasing: Transparent AA is a technique that can provide edge aliasing to transparent edges. Transparent edges such as alpha textures for instance have been a sore spot for many years since the introduction of multisampling. The idea is for the GPU to detect transparent textures such as leaves, grass, metallic fences (Half Life2) and properly provide anti aliasing to them. Nvidia offers both multisampling and supersampling aproaches to these new techniques which can have varied effects on the object being rendered. You can choose between multisampling or supersampling transparency or have it toggled from the control panel within the advanced settings tab.





Far Cry Comparison Shots


No AA Reference Image

http://www.nvnews.net/articles/chris...tx/g70noaa.png

Thoughts: This was a very difficult comparison to make. The hovering leaves and bobbing effect made taking an exact screenshot a bit difficult. Please bear with any minor inconsistencies you might see. While the results are not perfect I am very satisfied with what they represent.

2x AA Comparisons

2xAA/16xAF

http://www.nvnews.net/articles/chris...x/2xAAnorm.png

2xAA/16xAF (Gamma Corrected)

http://www.nvnews.net/articles/chris.../2xaagamma.png

2xAA/16xAF (Gamma Corrected, Transparent Multisampling)

http://www.nvnews.net/articles/chris...xtmaagamma.png

2xAA/16xAF (Gamma Corrected, Transparent Supersampling)

http://www.nvnews.net/articles/chris...xtsaagamma.png

Thoughts: With Far Cry I decided to focus on the leaf textures of the bush. As can be seen here. 2xAA does a reasonable job of cleaning up some of the aliasing along the beams. The textures of the bush however are not anti aliased at all. Once you enabled transparent multisampling, the aliasing is blurred out along the leaves. Under this circumstance it appears multisampling is more effective than super sampling.


4x AA Comparison

4xAA/16xAF

http://www.nvnews.net/articles/chris...x/4xaanorm.png

4xAA/16xAF (Gamma Corrected)

http://www.nvnews.net/articles/chris...tx/4xgamma.png

4xAA/16xAF (Gamma Corrected, Transparent Multisample)

http://www.nvnews.net/articles/chris...xtmaagamma.png

4xAA/16xAF (Gamma Corrected, Transparent Supersample)

http://www.nvnews.net/articles/chris...xtsaagamma.png

Thoughts: Seeing the usual step up from 2x to 4x shouldnt come as any surprise to anyone. However the impressive leap in quality from transparent multisampling should readily noticable on the leaf textures. Once again it seems transparent multisampling is doing a better job of removing edge aliasing from the bush.

8x AA Comparison

8xAA/16xAF

http://www.nvnews.net/articles/chris...tx/8xSnorm.png

8xAA/16xAF (Gamma Corrected)

http://www.nvnews.net/articles/chris...x/8xSgamma.png

8xAA/16xAF (Gamma Corrected, Transparent Multisample)

http://www.nvnews.net/articles/chris...Stmaagamma.png

8xAA/16xAF (Gamma Correct, Transparent Supersample)

http://www.nvnews.net/articles/chris...Stsaagamma.png

Thoughts: The nature of supersampling automatically gives a large quality enhancements to the bush leaves. It can still however cause a notable performance hit. Enabling transparent multisampling and gamma correction reduce aliasing to unseen levels in Far Cry.

Far Cry Multi AA Comparison Screenshot


Note: Special thanks to Clay for helping me with the multiple comparison.


Performance






Performance Thoughts: The first thing you'll notice is that a Geforce 7800GTX SLI setup is CPU limited up to 4xAA at 1600x1200 resolution. Meaning image quality enhancements are practically free. The 4xAA Gamma correction tests seem to be the oddball here. Showing a drop in performance thats not consistent with 2x or 8x. I imagine this is a bug as it only happens with Far Cry. The other thing you might notice is how there is a difference in performance drops with transparency AA based off the two map graphs. This is because of whats actually being rendered. Indoor Far Cry scenes such as archive do not generally have much foliage or transparent textures. And in this case there are none in the archive maps. The river map however is filled with trees, grass, and a great deal of transparent foliage. The hardware definately seems capable of detecting transparent textures and only taking additional rendering performance when neccasary.

Note: 8xAA has some troubles scaling with Far Cry. People with single cards should see a more consistent framerate drop when turning on 8xAA.

Minor Update: Gamma Correction performance at 4xAA is a known bug and will be fixed in later drivers. Gamma correction now occurs on the Nvidia DACS with no performance hit. Also just as with Half Life 2 there is also a known bug that causes textures to be missing with transparent supersampling. It will be fixed in future drivers.
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Last edited by ChrisRay; 06-26-05 at 06:29 PM.
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Old 06-26-05, 02:48 AM   #2
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Default Re: Geforce 7800GTX Anti Aliasing Investigation


Half Life 2 Comparison Shots


No AA Reference image



NoAA/16xAF

http://www.nvnews.net/articles/chris...gtx/hlnoaa.png

Thoughts: For these screenshots you may wish to adjust your gamma some. My reasoning for taking them so dark was to highlight the effects with various lighting conditions. Gamma correction would skew the results and defeat the purpose of the test. Keep in mind theres an odd bug with TSAA that is being fixed in future drivers. The fence line is white and without texture with transparent super sampling enabled.


2x AA Comparisons

2xAA/16xAF.

http://www.nvnews.net/articles/chris...x/hl2xnorm.png

2xAA/16xAF (Gamma Corrected)

http://www.nvnews.net/articles/chris.../hl2xgamma.png

2xAA/16xAF (Gamma Correct, Transparent Multisampling)

http://www.nvnews.net/articles/chris...xtmaagamma.png.

2xAA/16xAF (Gamma Correct, Transparent Supersampling)

http://www.nvnews.net/articles/chris...xtsaagamma.png


Thoughts: 2xAA represents a slight improvement to overall image quality. If you look across the power lines as well you can see a small improvement by the implementation of gamma correction. Transparency AA represents a significant improvement to image quality. Paticularly the super sampling implementation. While multisampling seems to have a lower overall effect. However there is much room for improvement.


4x AA Comparison

4xAA/16xAF

http://www.nvnews.net/articles/chris...x/hl4xnorm.png

4xAA/16xAF (Gamma Corrected)

http://www.nvnews.net/articles/chris.../hl4xgamma.png

4xAA/16xAF ((Gamma Corrected, Transparent Multisampling))

http://www.nvnews.net/articles/chris...xtmaagamma.png

4xAA/16xAF (Gamma Corrected, Transparent Supersampling)

http://www.nvnews.net/articles/chris...xtsaagamma.png


Thoughts: 4xAA shows a pretty significant overall improvement in image quality. Gamma correction provides a slight subjective improvement to the overall image including power lines. Transparent Supersampling once again making a significant improvement to the chain link fence.


8xS AA Comparison

8xAA/16xAF

http://www.nvnews.net/articles/chris...x/hl8xnorm.png

8xAA/16xAF (Gamma Corrected)

http://www.nvnews.net/articles/chris.../hl8xgamma.png

8xAA/16xAF ((Gamma Correct, Transparent Multisampling))

http://www.nvnews.net/articles/chris...xtmaagamma.png

8xAA/16xAF ((Gamma Correct, Transparent Supersampling))

http://www.nvnews.net/articles/chris...xtsaagamma.png

Thoughts: The supersampling nature of 8xS once again provides an instance boost to the overall scene effectively removing significant aliasing from the chain link fence. Enabling transparent super sampling creates a beautiful image with almost no visible aliasing.
Half Life 2 Multi AA Comparison Screenshot


Note: Special thanks to Clay for helping me with multishot.

Performance




Performance Thoughts: I realised that Half Life 2 would show signs of CPU limitation when next generation hardware came around. But I didnt realise it would be this severe. . There are rare cases where performance drops lower to what you see here generally providing excellent performance and image quality. Modern 7800 cards are significantly CPU limited in this title and can get away with 8xAA on SLI setups or 4xAA on non SLI setups with Transparency Supersampling enabled for unheard of quality improvements from anything we've seen before


Final Thoughts and Conclusions: For the last 7 months I have been pretty consistent in saying anti aliasing would take a back seat to new technology improvements. I am willing and happy to admit I was wrong about this. My biggest criticism with the current trend of raising sample pattern density was that it increased framebuffer consumption considerably. However the new modes are not only able to increase quality but they manage to do it without affecting performance too much. Add this to the fact that Nvidia has the best legacy anti aliasing modes available. I am left very satisfied by the improvements made to the Geforce 7800GTX. With these new modes transparent texture problems should be a thing of the past.

Final Note: I would also like to point out I took screenshots comparing World of Warcraft with Normal 4xAA and 4x Transparent Supersampling
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Last edited by ChrisRay; 06-26-05 at 06:43 AM.
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Old 06-26-05, 02:50 AM   #3
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

Well. That was some work. Hope you guys like it. Oh I unlocked the thread.
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Old 06-26-05, 03:03 AM   #4
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

Nice job Chris.
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Old 06-26-05, 03:10 AM   #5
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

very nice job.
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Old 06-26-05, 09:01 AM   #6
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

ChrisRay, the current driver have a bug that cause a performance drop with same games if you use gamma correction. nVidia already know this.
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Old 06-26-05, 03:29 PM   #7
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

ChrisRay, if you have Far Cry, could you check something?
This happened to me while playing
AA and AF from ingame setting.
TASS On on NV CP


TAMS on NV CP


Game is patched to 1.32 version, and gamma correction is on
Just interested to know if this a bug with (possibly) the patch, or the driver as Demirug mentioned
Feedback would be apreciated
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Old 06-26-05, 06:20 PM   #8
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

Quote:
Originally Posted by NoWayDude
ChrisRay, if you have Far Cry, could you check something?
This happened to me while playing
AA and AF from ingame setting.
TASS On on NV CP


TAMS on NV CP


Game is patched to 1.32 version, and gamma correction is on
Just interested to know if this a bug with (possibly) the patch, or the driver as Demirug mentioned
Feedback would be apreciated

Yes, its a known and documented bug. I found out the hard way too.

Quote:
Originally Posted by Demirug
ChrisRay, the current driver have a bug that cause a performance drop with same games if you use gamma correction. nVidia already know this.
Thanks. I was pretty sure it was. I couldnt see any other possible explanation for it.
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Old 06-26-05, 06:30 PM   #9
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

Chris, what drivers are you using, I cann't even start Far Cry (with 77.72))
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Old 06-26-05, 06:32 PM   #10
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

Same Drivers, Are you running Windowx 64 or something? Have you patched to 1.3?


*Edit* I made a few updates so the known bugs would better illustrated.

Chris
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Old 06-26-05, 06:35 PM   #11
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

Quote:
Originally Posted by ChrisRay
Same Drivers, Are you running Windowx 64 or something? Have you patched to 1.3?


*Edit* I made a few updates so the known bugs would better illustrated.

Chris

No just XP 32 bits. and I have patch 1.3, 1.31 and 1,32. The splash screen loads and then nothing.

Edit,
i just fixed it problem solved.
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Old 06-26-05, 06:45 PM   #12
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Default Re: Geforce 7800GTX Anti Aliasing Investigation

Quote:
Originally Posted by Skinner
No just XP 32 bits. and I have patch 1.3, 1.31 and 1,32. The splash screen loads and then nothing.

Edit,
i just fixed it problem solved.

What did you do? I havent had a single problem.
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