Anti Aliasing

[thegatekeeper]

I never really tought about this, but what is the difference between the different types of AA available?

When playing Company of Heroes, i got options like "8x CSAA", what is the difference between normal AA and CSAA?

Thanks, and sorry if it is a stupid question.

 

[rgeist554]

I've only heard of MSAA and FSAA. I think MS = Multi Sampling and FS = Full Scene. Honestly, I don't think you'll notice too much of a difference between the two. From what I understand FSAA is supposed to be the best one. :shrug: Anyways, I think AA (normal AA) is just the abbreviated version / general term that describes any type of AA (CSAA, MSAA, FSAA, etc.) I believe the only difference between them is how the hardware renders the image... I'm sure someone here is an AA expert though and can clear everything up.

 

[cusimar9]

I think there are 2 basic principles to anti aliasing.

Super or Multi Sampling is:

... a technique of collecting data points at a greater resolution (usually by a power of two) than the final data resolution. These data points are then combined (down-sampled) to the desired resolution, often just by a simple average. The combined data points have less visible aliasing artifacts (or moiré patterns).

Full-scene anti-aliasing by supersampling usually means that each full frame is rendered at double (2x) or quadruple (4x) the display resolution, and then down-sampled to match the display resolution. So a 4x FSAA would render four supersampled pixels for each single pixel of each frame.

The other approach is to attempt to 'filter' the image after it has been rendered. To attempt to identify jagged edges and smooth them with their surrounding pixels.

Supersampling (or FSAA) will always give you the 'best' result, post filtering approaches may give adequate result at a lower performance penalty.

 

[Sengoku]

Further clarification: CSSA is a Nvidia branded MSAA, that changes the when and what is sampled.

It effectively just tries to be smarter about what's sampled.

http://developer.nvidia.com/object/coverage-sampled-aa.html

One problem is that sometimes a game gives incorrect information about what kind of AA is active at a given time.

Maybe we should examine AA more closely in an article.

 

[thegatekeeper]

Thanks for all the info guys, so i wouldn't notice any difference between 8x CSAA and 8x AA in Company of Heroes?

 

[llama_man]

Only way to be certain is to try...

 

[purplerat]

I think the difference is in what the AA is applied to. FSAA would apply to everything I guess. I know in Crysis when Post Processing is set to high and very-high it applies AA to certain objects (I'm guessing the ones that really need it). It makes the game look very good even when FSAA is not turned on which is good because FSAA kills performance in Crysis.

 

[tomdrum]

yeh i was gunna say..i can only handle crysis at high with 2xaa which limits ths fps...but i cant see much difference without it on.

And are the nivdea control panel settings useful at all? there are quite a few options in there that i dont undersatnd lol

 

[nottheking]

There's actually quite a few AA terms thrown about...
■SSAA - Super-sample AA. Renders the entire scene with an increased resolution, then uses filtering to scale it down to the output resolution. Technically this method yields the most perfect result; the principle of scaling that way is the same to how, say, a digital camera takes an image at its own resolution, but with the equivalent of infinite SSAA. The downisde is that this is an absolute performance hog.
■MSAA - Multi-sample AA. Begins each render pass with a quick stencil check, making generally 2, 3, 4, 6, or 8 (though other numbers are possible) checks per pixel, at slightly different locations "within" the pixel. If it finds that all of them match the same polygon, then it renders that pixel normally without any form of AA. If It does find multiple polygons present in the pixel, it then it takes a sample of color from each point it'd checked earlier, and blends them together. This technically may not be as precise as SSAA, but the visual effect is almost indiscernible for most, and the performance drain is markedly reduced.
■CSAA - (something)-sample AA. This is a new type of AA, used by nVidia on their GeForce 8 cards. Technically, at heart, it's a form of MSAA, as it works in the exact same manner. HOWEVER, even though it will perform the initial stencil pass with 8 or 16 samples per pixel, when it needs to blend, it will only draw 4 of those samples, and then blend them together according to the ratio that the stencil pass found; a 16x stencil pass that found polygon A with 1 part, B with 3 parts, C with 5 parts, and D with 7 parts, would make one sample from each polygon, then blend them together at the aforementioned ratio.
■FSAA - Full-scene AA. This technically is not a "form" of AA; it refers to AA methods applied to the whole scene, as opposed to object- or line-based AA, which is not found at all in consumer graphics cards and commercial PC games.

 

[Heyyou27]

■CSAA - (something)-sample AA. This is a new type of AA, used by nVidia on their GeForce 8 cards. Technically, at heart, it's a form of MSAA, as it works in the exact same manner. HOWEVER, even though it will perform the initial stencil pass with 8 or 16 samples per pixel, when it needs to blend, it will only draw 4 of those samples, and then blend them together according to the ratio that the stencil pass found; a 16x stencil pass that found polygon A with 1 part, B with 3 parts, C with 5 parts, and D with 7 parts, would make one sample from each polygon, then blend them together at the aforementioned ratio.

It's coverage sampling antialiasing.