I feel like motion blur should be used like mouse acceleration. Like you said: If I whip my head around quickly that image should present clearly and immediately. However, if I'm in a car or flying through the air (in a game) this may distort the image as I'm glancing. This is the kind of drag-as-you-accelerate blur I'm expecting, and it can really make a fast-paced moment look that much more exciting. Motion blur is poorly executed everywhere.

> You can test this by looking at yourself in a mirror, focusing on one eye, then another. Do you see your eyes or face or anything blur?

This isn't the best test since your brain compensates for saccades by censoring input for a while. And it has built-in motion stabilization which allows you to read a sign while walking down the street.

A better test would be to look at your finger or hand while waving it very quickly. You'll see motion blur as your finger moves. In certain cases, you can see individual "frames" as an afterimage. E.g, if you look at a modern car tail light, the LED isn't on consistently but uses PWM to blink really quickly. So if you move your eyes while looking at a tail light at night, you'll see a series of dots rather than a blurry image. Once you learn this trick, you can distinguish between analog lights and PWMs by noticing if they are blurry or discrete.

I'm more referring to FPS obsession with blurring things when the character moves, for that, turn your head quickly: Do you see a blurry room? I do not. Because your eyes must also move, and as you say, the brain censors because a "turn and look" includes an eye movement (I hypothesize).

For fast moving things outside of ego motion, I can see a reason to use blur (e.g., your hand waving).

That's a good point, but how would turning your head in a first-person perspective ever look good in a game? As you say, when we turn our own heads our eyes naturally saccade. But I'm not sure having this done unnaturally -- e.g. by having a couple static intermediary images -- would look right at all. But smooth isn't right either.

It would rely on the eye's natural saccade. My brain drops the intermediate frames already and I mostly just see the new perspective. just like real life. Adding blur makes the motion stand out.

Except that your natural saccade is also wired to your motor neurons in your head and neck. For example, there's a strong connection between the neurons that fire to turn your head 10⁰ to the right, and the neurons that fire to turn your eyes 10⁰ to the left, which allows your eyes to fixate on something even as your head moves.

Indeed, it's almost impossible to turn your head slowly without your eyes fixing on points in your field of view, and then saccading to the next point. Try it. This is a hard-wired response. (You can perform some tricks to do it, like completely blurring your eyes, but that's not really the point.)

Meanwhile, if we watch a video with the camera turning, it's easy to keep our eyes staring straight ahead.

This shows that there is going to be a difference between a head naturally turning and watching a video of a head turning.

I think you're describing saccades as just being the "dropping out" of frames, and not including the extremely-relevant motion that our eyes do during a saccade.

I appreciate the attention to detail in this thread.

I think the only thing I can say here is - I dont see anything weird when I turn my head, and when FPS games added blur to "character moves his own body", it felt much less natural, not more. So, to answer question a few posts up "how would we do it?" I'd just say "The way we always have before we got enough GPU to make everything look like a movie"

> The way we always have before we got enough GPU to make everything look like a movie

Actually I think motion blur is more of a (futile) attempt to hide low frame-rates because we don't have enough GPU to render the ever more demanding scenes.

Just having a high frame-rate without (excessive) motion blur works pretty well. Perhaps it's not 100% realistic without eye movement but it's at least not as distracting as forced motion blur. I'm also not entirely sure that your eyes won't saccade in this case as they can lock onto moving objects just fine without body movement.

The point is that ego-motion-blur is dumb. (It can also make players motion-sick.)

You say it yourself: "your brain compensates for saccades by censoring input for a while. And it has built-in motion stabilization which allows you to read a sign while walking down the street."

I think the best implementation (without eye-tracking) would not motion-blur the entire scene when the player moves themselves (ego-motion-blur) but would blur moving objects. However, if the player's view motion happens to coincide with the motion of objects in the scene, for instance if the player is tracking the object (maybe another player so they can shoot it in an FPS) then the object-motion-blur should be reduced according to the degree of tracking. I'm sure some game engines already do this.

This was one of the interesting side effects of a small retinal hemorrhage. I had a fixed black spot (well, it actually looked a little like a thread) and the fact that it didn't move in my visual field made me realize just how many saccades you do.

Actually you do not see a new image, you see a amount of details and your brain rewrites the history of what you saw so there is continuity.

In video games, I find motion blur helps to compensate for lower framerates. It's particularly necessary at 30 fps, but nice even at 60 fps.

On the rare occasion I've been able to play a video game at 120 fps—my projector is limited to 60hz, sadly—I've found that I prefer to play without motion blur.

Motion blur is a contentious subject in games because it's often done very poorly.

The biggest three crimes are blurring an object too far, blurring things that shouldn't be blurred, and blurring an entire scene (which I guess just results in #2, so maybe there's really only two crimes). The most important thing is that motion blur should be subtle. Properly-done motion blur doesn't make a game look blurry, it makes it look more real and smooth.

If an object is moving 50 pixels between frames, then the blur should not be more than 50 pixels wide. Really, it should likely be only 25 pixels to make the blur more subtle. But for some reason, racing games love to apply a full radial blur to an entire scene while going fast, and to me it just ruins it.

Likewise, an object that is not moving relative to the camera should have no motion blur at all. This is where so many games get it wrong. As you rotate, they blur the scene using post-processing. In a completely static scene, this makes sense and is a very computationally-efficient way to perform motion blur. But if you're rotating because you're tracking an object, the tracked object should not be blurred. If you're in a racing game and the car next to you is going the same speed as you, the other car should not be blurred.

Really, the only guaranteed way to get correct motion blur is to render multiple entire frames in a row and then blend them, but you need a LOT of samples to make this look good, or else something like a vertical line looks like a series of vertical bands as it flies across the screen, rather than a smooth blur.

The best is probably a hybrid approach. Render each object in the scene on its own and apply a post-process blur on a per-object basis based on which direction it is moving relative to the camera. Though Z-ordering could end up becoming a major challenge.

> As you rotate, they blur the scene using post-processing. In a completely static scene, this makes sense

No, it doesn't make sense because due to eye movement that's not how turning looks in the real world. Any game that blurs the scene on camera rotation is doing it wrong even if nothing else is moving at the time.

It's impossible to do it correctly without very low latency and high precision eye tracking so the best you can do is to not blur anything that the player might be focusing on.

Games are not the real world. When you play a game, you are look at an image. For the current topic, motion blur in games is like motion blur with a camera, not like when you turn your head.

It's photorealism, not realism.

Games however are not movies either. Specifically, they are interactive and thus have different requirements on their visual looks. Most games are also expending significant effort trying to make the experience as immersive as possible and simulating looking trough a film camera works against that. Camera motion blur, film grain, lens flares and other such effects should have no place in games where you play a human or human-like character rather than a robot.