Spatial AA vs. Temporal AA

[Gunhead]

After ATI's new AA technique, I'm somewhat confused about these terms. Can somebody post good clear definitions of these? Have they been defined clearly?

Way I have understood the two so far:

You do Spatial (space) AA when you oversample a source during the rendering and then combine the samples for final output. This is done to eliminate jaggies and other spatial artefacts that result from undersampling the "infinitely accurate" geometry and shader math and "finitely accurate" texture art.

You do Temporal (time) AA when you sample the source at many consecutive points in time and then combine the samples for final output. This is done to eliminate wheel spinning in wrong direction, jerky looking output (lack of "motion blur") and other temporal artefacts that result from undersampling in the time dimension.

I have kinda thought (I don't know why exactly, maybe some 3dfx slides or something...) that the two are quite distinct methods; and especially that it doesn't count as TAA if you don't do a combining of the temporal samples before display. (How else are you going to e.g. produce a controlled motion blur effect?)

I don't know if this is any kind of issue really, but I'd be grateful if my muddy thoughts on this got clarified

So, any definitions and/or contrasts of SAA and TAA?

 

[DemoCoder]

ATI's method tries to use your display device or eyes as the "final combine/accumulation buffer"

True temporal AA as used in offline renderers requires way more samples. As such, the "real time" TAA being used only works on relatively immobile parts of the scene and only if the refresh rate is high and consistent.

The biggest gains from TAA are missing: motion blur. This is one reason why a 24fps CGI scene with high degrees of temporal antialiasing can look better than a CGI scene at 60fps with no TAA (no motion blur)

 

[Gunhead]

To clarify the question... I'm not asking what ATI does in their particular method, I'm asking about any commonly accepted definitions. I think I have understood the ATI method, thanks to B3D's preview, but I'm just still a wee bit uncertain whether the effect it creates is enough to classify it as a bona fide TAA method. If there are such classifications. Hope you understand what I mean here

 

[DemoCoder]

That gets into semantic arguments and what one versed in the field would think if you asked them what TAA means.

My personal opinion? Yes, it's a form of Temporal Antialiasing. But I think they should have came up with a different term for it, like with all the various terms we have for spatial AA modes (OGSS, OGMS, RGMS, RGSS, JGSS (jittered), programmable, stochastic AA, etc)

Someone who's used to TAA from offline renderers will be confused.

 

[Gunhead]

DemoCoder, thanks for the clarifications. I hope it's obvious my previous reply wasn't to you but to my original post

It's especially the lack of Motion Blur capability that makes me uncertain whether ATI's method is a "TAA method". Maybe they should have labeled it "Temporo-Spatial FSAA", yeah really rolls off the tongue

 

[Gunhead]

That gets into semantic arguments and what one versed in the field would think if you asked them what TAA means.

Actually I'd be very interested in these!

My personal opinion? Yes, it's a form of Temporal Antialiasing. But I think they should have came up with a different term for it, like with all the various terms we have for spatial AA modes (OGSS, OGMS, RGMS, RGSS, JGSS (jittered), programmable, stochastic AA, etc)

Someone who's used to TAA from offline renderers will be confused.

I have a feeling that this might be the consensus here...

When I post this, wait a minute so I can get on track with the thread, it goes temporally ahead of me at the moment [Edit: ah, no problem.]

 

[Simon F]

Gunhead,
You are correct. As usual, the problem is some ill-informed have managed to pick up a well defined term and use it incorrectly. (The term, HSR, is another classic)

You can, of course, do both things at the same time, eg Pixar's stochastic sampling where they jitter samples in time, position, depth of field etc etc.

ATI's method could, perhaps, be better described as a multi-pass spatial AA method (with bio-CRT filter )

 

[DemoCoder]

Boy, does anyone remember the war over the term "Multisampling" back in the 3Dfx days?

 

[KimB]

From what I understand, "real" temporal AA, as it's used in offline renderers, is a form of motion blur. It's basically rendering the image at a much higher framerate than the final display, and sampling down to the fewer final rendered images.

I'm sure you can see the parallel between this and supersampling, which is, effectively, rendering the image at a higher resolution than the final display, and sampling down to the smaller final image. This is why it's termed "temporal antialiasing" instead of motion blur (which has a more negative connotation).

The temporal AA that ATI is doing would probably better be termed "jittered AA" or something similar.

 

[arjan de lumens]

What ATI is doing with their 'temporal anti-aliasing' would IMO more correctly be referred to as a kind of 'temporal dithering'.

 

[Basic]

Add one more vote for "this hasn't got anything to do with temporal AA". But I must admit that I've said it myself (with a slight hidden disgust ), just because that was the term people expected.

"Time dependent spatial AA" would describe it quite well, but it's a bit long.


Btw
Definition of "texel" anyone?

 

[Bolloxoid]

The term temporal antialiasing is incorrect for Ati's new offerings as the technology is not for reducing temporal aliasing. It's purely for reducing spatial aliasing, albeit by varying the sample pattern in the temporal domain.

Temporal antialiasing = something that reduces temporal aliasing.

Spatial antialiasing = something that reduces spatial aliasing.

The actual technical methods used to achieve that are irrelevant with respect to the definitions.

 

[Ailuros]

Gunhead,

Would this link help?

http://freespace.virgin.net/hugo.elias/graphics/x_motion.htm

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Sidenote: another thing I'd like to note is that in recent games we see more than often features like "motion blur". Now someone correct me if I'm wrong but it's usually motion trail and not actual motion blur. Or better as a friend defined it:

motion blur = temporal antialiasing
motion trail = temporal blurring

 

[davepermen]

Sidenote: another thing I'd like to note is that in recent games we see more than often features like "motion blur". Now someone correct me if I'm wrong but it's usually motion trail and not actual motion blur. Or better as a friend defined it:

motion blur = temporal antialiasing
motion trail = temporal blurring

yes, indeed. if you run stuff at low res, you can have today tons of fps, and, with vsync, you can create tons of stuff like that with it. antialiasing, both temporal and spacial (and even dropping anysotropic filtering needs due that).. quite interesting _other_ direction to develop, imho.. instead of cranking up resolution and aa and af, go down back again, and draw simply tons of frames, and then use statistical approaches to evaluate what you see out of it.. looks much more movie-like imho.. (espencially as tv's are hell lowres anyways..)

 

[Ailuros]

Trouble is that I haven't seen any real motion blur this far in any game, albeit I'd love to.

The so called motion blur in NFS: Underground (actually motion trail) was a pathetic blur implementation; in fact it's so bad that it doesn't only add to realism, it makes driving at high speeds eventually harder for me. MotoGP2 was the same. I've driven both cars and motorcycles at ludicrous speeds through the years and I know that real time doesn't definitely look even close to that.

 

[John Reynolds]

I've driven both cars and motorcycles at ludicrous speeds through the years and I know that real time doesn't definitely look even close to that.

Someone's watched Spaceballs a few too many times. 8)

 

[Bambers]

I've driven both cars and motorcycles at ludicrous speeds through the years and I know that real time doesn't definitely look even close to that.

nah, it adds to the stoned feel



When I first saw the mention of temporal AA I initially thought ati had implemented a motion blur into the drivers.



as for real motion blur in games, I don't think it's been implemented becuase it's not worth it.

While 24fps with motion blur may look better in a film than 60fps without once you start interacting the 24fps is going to feel like crap nomatter how good the motion blur. Unless you've got spare fps over the monitors refresh rate then motion blur is a bit pointless really

 

[davepermen]

motion blur adds a LOT even to 60fps.. even to 80fps.. you still "get the individual image" even while it looks like motion. and the trick is, the individual images your brain get, are motionless.. with motion blur, they are not. this helps a LOT and gives a very different, much more dynamic interpretation of what you see..

if q3 would be as available as q1 and q2, i guess we'd have a lot of mods for such thing. thinking of the 500fps you can get in q3, thats enough to get nice motionblur to 25fps easily (and you can do "temporal aa" with it, as well)

the more we get into HDR rendering, the more motion blur mathers, as at high range light changes, motion trails get very visible, and distortet, in motion.

we'll see....

 

[Diplo]

I find half a bottle of a fine single-malt is a far more pleasant way to simulate motion blur - and it works outside the realm of the video game, too

 

[trinibwoy]

Temporal antialiasing = something that reduces temporal aliasing.

Spatial antialiasing = something that reduces spatial aliasing.

What exactly is Temporal aliasing? Is it unwanted motion trails ala NFSU? Are there any games that exhibit this now or will it only become noticeable with HDR games as mentioned above?