Nick Spolec
Newcomer
Didn't Metal Gear Solid 2: Substance (PC version) feature motion blur? Or was that just motion trailing?
Spatial AA vs. Temporal AA
- Thread starter Gunhead
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Joe DeFuria
Legend
Xmas said:
I'll just expand on that a bit, for the benefit of those who may not understand the implications of what you said.
The "classic" demonstration of temporal aliasing artifacts is the "rotating wagon wheel." If you've ever seen a motion picture where there's a wagon wheel spinning, espcially as it's changing speed (or maybe helicopter blades is more relevant for today's time), you've seen the "the spokes look like they're moving slower...and actually spinning backwards!" When in reality you know they're moving forward very fast.
That is an aillustration of temporal aliasing. Because film is only captured at 24 FPS, you only get "24 snapshots per second" to try and convey the idea of motion, when the ideal is to have infinite frame rate.
Imagine a wagon wheel with only one spoke, turning at exaclty 24 revolutions per second. If you took a "snapshot" every 1/24th of a second...it would not look like it's moving at all.
With film, there is already some form of temporal AA, because shutter speed is not "instantaneous." This introduces motion blur, which is a form of temporal AA. The problem of Temporal aliasing with 3D rendering is much larger, because the computer draws a "perfectly non-blurred" image every frame, which would be the same as an instantaneous (infinitely small) shutter speed on movie cameras.
Here's a question for you. Can you do a motion blur via Smartshader?
Joe DeFuria
Legend
The Baron said:
Not a true motion blur in the sense that it would do legitimate Temporal AA.
To do it properly, you'd need to have access to several frames of completed frame buffer data over a period of time. AFAIK, smartshader effects are limited to basically post processing a single frame of data.
So you'd probably need to design the hardware specifically for it? Or could that be done on the software level?
So you can only access a single frame. Thought so, was never really sure.Joe DeFuria said:
Flight sims and racing games. They both contain pretty obvious examples.trinibwoy said:Excellent explanation Joe. Thanks. Has anyone ever noticed this in a game though and if so tell me so I can go look for it
The Baron said:Flight sims and racing games. They both contain pretty obvious examples.trinibwoy said:Excellent explanation Joe. Thanks. Has anyone ever noticed this in a game though and if so tell me so I can go look for it
Thanks Baron. Never stared at the prop in IL-2 before but I'll check it out now.
Joe DeFuria
Legend
trinibwoy said:Excellent explanation Joe. Thanks. Has anyone ever noticed this in a game though and if so tell me so I can go look for it
In games, it maifests itself in different ways (other than the obviously related fast rotating objects). The subjective way to describe the effects of temporal aliasing, is that the animation doesn't look "fluid and smooth". It looks "jerky", not natural. It's one of those things actually, that you may not even really notice too much until we get temporall AA, and then it'll be tough going back.
Have you watched Gladiator?
You can actually see what I'm talking about if you watch some of the fight scenes. They are (from what I can tell) shot with high speed film / shutters, which makes the visuals *very sharp* for artisitic effect.
The consequence is, if you noticed, it doesn't look quite "natural". There's a sort of "non fluidness / jerkyness" to it, particularly noticable on the big screen at 24 FPS.
http://www.beyond3d.com/forum/viewtopic.php?t=11889&start=422The Baron said:
As I said there, it could be done better.
It would only need slight changes to smartshader to make it more efficient.
Here's an example:trinibwoy said:
Let's say I'm playing an old game, like Quake 2. The game's framerate is capped at my refresh rate. This is great, but I notice a problem. As I strafe around a corner to snipe some robotic thingies, I notice that I see "ghosting" of the corner of the wall. I see multiple images, similar to a crappy motion blur effect.
As another example than you can test yourself effortlessly, wave your hand in front of the monitor, then wave it in front of the wall. You should notice that something looks very different when it's waved in front of the monitor: you'll see your hand in multiple discreet steps, instead of a smooth blur (note: this will only work with a CRT, not a flat-panel).
This is temporal aliasing. It comes about because each frame is taken at a single, discreet time (this is similar to the spatial aliasing that occurs as a consequence of sampling each pixel at a single, discreet position).
Good motion blur will serve to smooth these multiple images out, removing the artifact of seeing multiple discreet images at once. A simple accumulation buffer approach, of course, will not do this. It simply removes the limitation of the monitor's refresh rate on framerate. A simple accumulation buffer approach is exactly analagous to an ordered-grid FSAA technique. It may help in some cases, but will totally break down in others.
A better temporal AA technique would break up the aliasing by not rendering discreet frames. One example that I saw was a technique wherein for each frame displayed, ten would be rendered. Each of those ten frames would randomly select 1/10th of the pixels on the screen to be rendered, leading to a stochastic blend between frames. One could combine this with 10x supersampling to remove any "gritty" effects this would cause.
One more link:
http://www.beyond3d.com/forum/viewtopic.php?p=19824&highlight=motion+blur#19824
In fact those that hadn't read the thread back then, it's an interesting read even today.
http://www.beyond3d.com/forum/viewtopic.php?p=19824&highlight=motion+blur#19824
In fact those that hadn't read the thread back then, it's an interesting read even today.
A well known example in films/video are wagon wheels or helicopter blades going backwards instead of looking blurred.trinibwoy said:
I should think that all games with (fast) motion 'feature' it.
Another simple example is having an enemy on the other side of a wall run past an opening. Sometimes you might be lucky and see him in the gap for a brief period, other times, maybe not. If you had temporal antialiasing you would see the "blur" as he rushed by.
davepermen
Regular
trinibwoy said:
it's the fact that an individual frame is 100% sharp and has no motion in it, as it captures only a moment in time, instead of the timeslice between two moments (last frame moment and this frame moment), as a camera does. this leads to blurred individual frames, but if you watch them as a whole, they look perfectly sharp, and moving.. (watch a movie and press stop at a strong moving frame. _THATS_ a temporal antialiased frame.. take a screenshot of your favourite game while in full motion, thats a temporal aliased game)
