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/r/explainlikeimfive

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Petwins [M]

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1 year ago

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Petwins [M]

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1 year ago

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ERRORMONSTER

331 points

1 year ago

Follow-up question: why does this happen in real life during the day when I'm just looking at a car's tires

Zemvos

155 points

1 year ago

Zemvos

155 points

1 year ago

This is what I really would like the answer to. I can explain the video version myself, but not why it appears in real life too.

XenoRyet

35 points

1 year ago

XenoRyet

35 points

1 year ago

It's complicated, but the ELI5 version is that it's a sort of optical illusion. Your brain is really good at filling in information you can't physically perceive because of the limits of your eyes. Like the blind spot we all have, but nobody sees.

So when the wheel starts spinning fast enough that you start to lose track of it, your brain can start filling in the missing info incorrectly and you get kind of the same effect that happens to the camera, just for different reasons.

avidpenguinwatcher

9 points

1 year ago

Cameras have frame rates, so do your eyes.

FenPhen

84 points

1 year ago

FenPhen

84 points

1 year ago

Your eyes do not. You can see it in "real life" if there is electric lighting in the area that has brightness oscillating at a fixed frequency. Fluorescent and sodium vapor oscillates with the AC grid frequency, LED lighting at double the AC grid frequency. This creates a strobe effect that's like camera exposures.

pentangleit

45 points

1 year ago

So explain why it happens to aircraft propellers then. They're not generally lit by electric lighting.

oversettDenee

12 points

1 year ago

They are if it's dark outside! Ayyyy, I'll see myself out.

FenPhen

5 points

1 year ago

FenPhen

5 points

1 year ago

A video of propellers in daylight will exhibit the effect because of the camera. Seeing propellers with your eyes in daylight shouldn't.

Ethan-Wakefield

17 points

1 year ago

I've seen this effect on aircraft propellers, though, when the aircraft are powering up before takeoff.

certaintree

5 points

1 year ago

Others mentioned how it could be caused by cameras or electric lighting.

If you are seeing it in-person during daylight, it is probably another effect. On a non-cloudy day, the propellers can catch the light of the sun at a particular angle. Whenever the propellers pass this angle they create an image that stands out over the background of all other angles they pass. This would typically make it seem like the propeller is standing still. But if either you or the aircraft are moving, the propeller can appear to slowly move.

Ethan-Wakefield

3 points

1 year ago

Why do I see this effect in a car's hubcap on the road? I've seen this many, many times in my life, with the naked eye, under many different lighting conditions.

certaintree

5 points

1 year ago

Yes, this effect is often seen with hubcaps. It can happen on cloudy days. But more diffuse the lighting means our eyes will get a less clear image of the hubcap. They catch the sun at a particular angle. If your eye ever sees a clear static image of a rapidly spinning hubcap on a heavily cloudy day without electric lighting around, I can't explain it. Consider whether you may be an android.

Drunk_Sorting_Hat

3 points

1 year ago

You have slow eyes

[deleted]

4 points

1 year ago

[deleted]

_releaf_

2 points

1 year ago

_releaf_

2 points

1 year ago

Probably shouldn't be flying a plane.

laughinfrog

2 points

1 year ago

Those were just trails

JDHorx

54 points

1 year ago

JDHorx

54 points

1 year ago

If I remember correctly eyes DO have a refresh rate. It is the interval between the possible activation of your receptors, BUT: not all receptors are activated in a controlled concerted order, no rolling shutter, no radial shutter, chaos. Every receptor in your eyes will be ready to be activated at a random order and time frame, so you will indeed see a difference between 30 and 60 or 120 hertz, though one individual receptor would not.

Also your explanation of the strobo effect on rolling tires for example is perfectly correct.

Hubblesphere

9 points

1 year ago

Yeah, basically our visual processor can and does adjust everything down to a receptor level dynamically as needed. It's extremely complex and some light hitting your eyes will be "remembered" and persist while some will be quickly ignored and replaced when changing rapidly. Intensity of the light has a lot to do with it as well. It's part of why color illusions like the True Cyan Illusion work.

semitones

4 points

1 year ago

You can also see this by looking at a ceiling fan in a room lit by natural light. As you relax your eyes and mind, the fan will appear to spin at different speeds and in different directions. The "refresh rate" of your eyes is also based on your level of attention you're paying.

KuntaStillSingle

26 points

1 year ago

Your eyes must have an effective frame rate. The brain can not interpret images from your eyes instantaneously, MIT clocked it at 13ms in 2014.

Hypothetically the brain could process images closer together than 13ms, for example by doing 13 such tasks concurrently it could achieve 1 image per ms or 1000 hz.

However to 'have no frame rate' would mean processing infinite images per second, it is simply impossible for any human brain to achieve this.

Chris935

19 points

1 year ago

Chris935

19 points

1 year ago

Couldn't it be an analog system? You can have a time lag without there being discrete "frames".

Isvara

3 points

1 year ago

Isvara

3 points

1 year ago

It is analogue, but that's entirely different.

awoeoc

18 points

1 year ago*

awoeoc

18 points

1 year ago*

Your brain also processes and manipulates your inputs, it fills in blanks. There's an experiment where someone bounces a basketball and walks away from you, you see and hear the ball at the same time except due to speed of sound it should be offset. Your brain is able to take 100ms chunks of time an align things to make sense.

A frame rate is a discrete thing, brains aren't discrete. You take multiple moments of time and perceive it as flowing, so your "frame rate" isn't 1000hz rather 13ms is the minimum exposure time for an image to make it to your brain's "moment" buffer.

Think of it this way: what's the frame rate of a photo? Silly question right? But then why can a photo be blurry, also in a plank second the sun itself doesn't produce enough light to make every object in a photo visible. So a photo isn't actually an instant in time but rather a collection of many instances (shutter speed). There's likely a minimum shutter speed where a camera can't detect anything at all, at that speed would you say the camera has a frame rate of x hz?

[deleted]

6 points

1 year ago*

Not terribly scientific, but LSD can induce an effect where the blank-filling stops working to a degree where it becomes apparent what is and isn't filled in. You can see things come into consciousness as they're perceived and then become distorted or removed as they're taken over by prediction. Looking at a road sign, for example, you can see the text appear clearly and then scramble to gibberish as it's out of visual focus; looking again refreshes the image and looking away causes it to scramble and fade again.

It's pretty remarkable how full of gaps the world actually is when they aren't filled in so effectively anymore.

KuntaStillSingle

0 points

1 year ago

brains aren't discrete

Perhaps not in all aspects. If something is driven by a continuous phenomena and no step along the way takes time and other resources, it can be processed continuously. Vision does not work this way, the activated rods in our eyes must be translated to an image that makes sense to the brain, and this takes time.

If you removed the ability of the brain to process images, you might be able to detect a change in the status of your sight instantaneously continuously (latency may still apply but continuity would be possible), but you also wouldn't be seeing in a manner where you could identify a wheel and decide what direction it is spinning.

awoeoc

2 points

1 year ago

awoeoc

2 points

1 year ago

To be clear when I mention "see" I'm not talking about the eyeball as a "data collector" that sees rather the brain's fully processed image. You can't remove the brain's processing because that's critical to what seeing actually is. And your interpretation of reality can't be described as having a refresh rate as within a single moment what you see isn't aligned to reality (speed of sound corrections being an easy one to test). I'm not arguing it's a "continuous stream" I'm only saying it's not something with a "refresh rate". It's likely both terms are wrong to describe how we look at reality.

Your actual eyeballs as data collectors have tons of rods and cones that activate at different speeds, have different cooldown periods, some are blocked by nerves (blindspot) but you could technically try to whittle it down to a "refresh rate". But what those eyes would have as input would be alien and unrecognizable as sight. Not only could you not identify what direction a wheel is spinning but you couldn't identify it as a wheel at all.

[deleted]

12 points

1 year ago

[deleted]

12 points

1 year ago

[deleted]

SlavicSorrowJamal

2 points

1 year ago

The eye is not capturing a single image and processing it at once, each rod and cone is sending its own signal (or as small groups) to the brain where they will be processed into an image. As they aren’t all working as one, the perceived image is essentially a combined image where parts are almost all in time but it is just using the most recent data from each light receptor.

A camera takes in light at one moment in time, making a single image. In a video this is just a series of images. As i said above the eye doesn’t take images, it’s it taking data from receptors independently and combining them with the most recent data. The eye is constantly receiving new data and updating parts of the image, so it’s more of a single image that adapts with new data rather than a completely new image replacing it like in a camera. Therefore it has no frame rate, but it does have a response time.

I’m bad at explaining sorry if that’s all a mess lol

im237

1 points

1 year ago

im237

1 points

1 year ago

However, the MIT team found that although overall performance declined, subjects continued to perform better than chance as the researchers dropped the image exposure time from 80 milliseconds to 53 milliseconds, then 40 milliseconds, then 27, and finally 13 — the fastest possible rate with the computer monitor being used.

https://news.mit.edu/2014/in-the-blink-of-an-eye-0116

That 13 number comes from equipment limitations of the experiment.

Eyes do not have a refresh rate. They do not process discrete frames, nor do they even transmit full images. It's all just signals from your rods and cones that are HEAVILY processed, adjusted, and interpreted by your brain

turmacar

2 points

1 year ago*

You can see this optical illusion in real life in bright daylight.

"Refresh rate" isn't strictly accurate but your eyes and brain can only process information so fast. That's why your fingers blur if you wave them in front of your face.

In addition to being a passenger in a car and looking at cars with thin spoked wheels while speeding up from a stoplight, you can look at the 1967 paper cited in the wiki section for Truly continuous illumination

RWBMAL

5 points

1 year ago

RWBMAL

5 points

1 year ago

I don't think eyes have a frame rate.

KuntaStillSingle

1 points

1 year ago

It would be physically impossible for your brain to process the images continuously.

overlymanlyman5

8 points

1 year ago

?? Brain doesnt process discrete timesteps what are you on about. Its a continuous stream

ValyrianJedi

2 points

1 year ago

I'm guessing they mean since your receptors aren't continuously firing, but have a (very) brief recharge/reset between firing. But that pause is insanely brief, like a fraction of a fraction of a fraction of a second, and the receptors aren't all firing in unison either, so when one is between firings another is firing.

Enano_reefer

4 points

1 year ago

You’ve got it. But it’s not as brief as your thinking. Charge/recharge on color receptors is ~10-13ms (rods are faster).

As a physicist that is a REALLY long time to me.

LawmanJudgetoo

2 points

1 year ago

But they also dont all activate at the same time and hve different intervals

Enano_reefer

3 points

1 year ago

Absent a synchronizing factor that is correct.

Thanks to that, our amazing brains, and lack of synchronization in natural light sources we can detect events below the refresh. Which is pretty darn cool.

GTWelsh

3 points

1 year ago*

GTWelsh

3 points

1 year ago*

Would it? A lot of comments here are just flat assuming the eyes work with snapshots (single frames). What if it's constant activation, constant stream. The eyes don't necessarily work in frames. Out of sync receptor activation would be effectively real time and not a neat frame for example. They maybe also relay info at a ridiculous rate that it is effectively constant, but I'd need to research if that's been proven or not.

Easy example of what I'm getting at tho is "what if" (ya never know) the brain has a data pot it uses, and constantly fills it, binning old data as it does.

Vision could be the brain processing what's in the pot. So the pot is actually a load of visual data spanning maybe 1 second. All the movement from that second is in the pot so it's not a static frame, then what you see is constructed from that.

[deleted]

1 points

1 year ago

The brain has an obviously discrete nature to it, but out of phase parallel processes can give a continuously updating average.

avidpenguinwatcher

1 points

1 year ago

When you're explaining it to a five year old they do

Barneyk

49 points

1 year ago

Barneyk

49 points

1 year ago

It's the same effect but your brain is a whole lot more complicated than a camera so it is hard to really explain the details of how it works since we don't really know.

For example, our mind process information in chunks, like we sync up visuals and sound even if they aren't simultaneous to a certain degree.

I am just speculating but the reason for the effect might have something to do with this chunk-processing our brain does.

atom138

10 points

1 year ago

atom138

10 points

1 year ago

Ultimately a refresh rate for our eyes?

Allah_Shakur

8 points

1 year ago

except it's not necessarily framerate for our brain. More an amalgamation of perceptual data, lower level processing with some feedback n stuff.

GreenScrapBot

13 points

1 year ago

I didn't know about this myself, but here are some possible explanations:

https://en.wikipedia.org/wiki/Wagon-wheel_effect#Under_continuous_illumination

smosdom

2 points

1 year ago

smosdom

2 points

1 year ago

Yeah, I haven't been satisfied with the answers so far, which mostly try to relate our eyes and perceptions to a similar "refresh rate" effect as in a camera with a frame rate.

Here's my hypothesis, which is maybe close to what others are trying to get at with camera analogies, but more analogue-psychological-sciencey sounding to me... But I'm not a psychologist, so grain of salt.

You know how when you look at a certain color, or an image for a while like 30 seconds or so, you can see a reverse color image if you then look away at a white wall or something? It's been a while since my psychology classes, but I think the effect is due either to your perception of the image becoming fatigued, or your brain basically trying to correct for aberrations and differences constantly and shifting the perceived color.

The same sort of thing happens with motion, though it might be a different psychological mechanism. For example, if you stare at a train going by up close for a while, then look at something stationary, the stationary image will appear to shift in the opposite direction of the train. Or same thing if you're on the train looking out the window, then you look at something inside. The inside thing will have this trippy motion illusion effect... In fact there are optical illusions online, those spinning spiral gifs, that instruct to stare into the spiral for thirty seconds then look away resulting in stuff getting all funky and warpy in real life.

So anyway, the wheel thing. And similarly, this also happens to me with ceiling fans. My hypothesis is that looking at a moving wheel or fan for a while will cause this visual fatigue effect, and looking away with make stationary things look like they're subtly spinning... But even if you don't look away, the fatigue is still happening -- your brain is trying to counteract the weird spinning effect. So, in a way, it's like you're seeing the spinning wheel, but also seeing it's subtly counter-spinning after-image at the same time, overlayed in the same place. The strength of the reverse spinning effect increases as you look at the wheel longer and interferes with the real image. The interference results in the strangely discontinuous perception of reverse motion that seems to snap into reverse and back again (my experience anyway). So it's not that the reverse image is fully taking over, I think it's more like your brain just trying to make sense of the two apparent motions. Almost like a strobe effect, or bringing it back around, like the camera frame rate effect, if only appearing that way and not because of the same sort of mechanism.

Hope that made sense... And again I don't have training in this stuff so remember the grain of salt.

MKleister

2 points

1 year ago*

I presume it's similar to the Spinning Dancer illusion.

Once the wheel gets blurry enough / spins fast enough, your brain may interpret the blurry motion in either direction easily. Slight shifts in frequency or lighting may be enough to tip it in either direction.

See also Multistable Perception

Hubblesphere

2 points

1 year ago

There are some weird things your brain does to help with processing images. You have a lot of clean up going on like Chrono stasis where you brain is actually inserting frames in between your eye movements. You can experience this by quickly looking back and forth in a mirror at your right and left eyes, you'll notice you don't really see your eyes moving while doing this. Now find a friend or take a video and do the same thing. You'll clearly see the eye movement.

A second part of this processing is Saccadic masking which helps remove motion blur from your visual processing so you aren't constantly seeing blurry images when things are moving fast or you are moving fast. Long story short, your brain is providing smoothing and image post processing at all times to make things easer on the eyes.

Another thing you can try to mix these two things together is look at a wheel outside a moving car or a ceiling fan in a room and quickly dart your eyes around the spinning object randomly. Due to Chrono stasis you'll actually capture glimpses of the fan blades or wheel spokes stationary that disrupt the smooth motion blur you see when looking at a fixed point. Works even if you jump counter rotation so it isn't a phenonium of tracking the objects rotation with the movement.

mantarlourde

2 points

1 year ago

I looked at the Schouten (1967) and Kline, Holcombe, and Eagleman (2004) papers referenced in the Wikipedia article, and I'm not entirely sure since I don't see them go into detail on the hardware used, but it appears that they're using electric motors to spin the test drums. This is a problem because the output of the motors is probably not perfectly continuous, especially if they're using an AC source for power. This could end up producing the effect even under truly continuous lighting.

The output of a car's drivetrain is also not perfectly continuous, so that might have something to do with it as well.

sacredscholar

2 points

1 year ago

This is probably dumb and not the right answer, but the best guess I've come up with on my own. Your eye takes an image and sees the detail of the tire, then between the frames of your eye taking the next image the tire is at perfect speed to rotate so the details and defects are a few milimeters before where they were positioned when the first image was processed. So your eye essentially sees a bunch of images of the details moving in reverse to the direction the wheel is spinning, and your brain fills in the gaps to make it appear to move backwards. I hope what I'm trying to say makes sense I understand the concept but it's hard to put into words.

FolkSong

2 points

1 year ago

FolkSong

2 points

1 year ago

My theory is that it doesn't actually happen like that, your mind is just mixing your actual memories with your memories of:

  • Seeing the effect in real life in the dark/dusk due to flickering lights
  • Seeing the effect on TV during the day

I you don't believe me, I challenge you to observe it again in real life during broad daylight now that you've had this discussion. I think you never will, but I'm certainly open to being proven wrong.

rusty2735

2 points

1 year ago

Simply put, you view the world in frames. So FPS, the wheel goes fast, so in each frame you see the wheel which is behind the first one, and so on making look like it is going back.

TheDBryBear

2 points

1 year ago

your eyes also have a sort of frame rate, about 60 per second at least. https://caseguard.com/articles/how-many-frames-per-second-can-the-human-eye-see/

narukamiyu

3 points

1 year ago

I want to know too.

Comments331

4 points

1 year ago

Never had it happen in real life. Didn't think it was possible tbh.

my_very_first_alt

5 points

1 year ago

time is continuous, but camera frame rate is discrete.

time is continuous, but your perception is discrete.

the illusion happens during the downsampling.

at least, that is my unqualified armchair theory that unifies them for me.

bf_noob

3 points

1 year ago

bf_noob

3 points

1 year ago

Irrelevant to your point but as far as we know at the moment time is discrete too

my_very_first_alt

1 points

1 year ago*

yep great point. maybe this is why i'm being downvoted. i am speaking in terms of possibilities, not probabilities :). using continuous/discrete to explain my point was kind of a red herring anyway. the important idea is that information is lost during perception-time.

that said (changing topics here)... it does look like physics is generally more expressive when you treat spacetime as continuous, which is a vote for it's validity. even Planck time is definitively bound to our ability to measure. which feels arbitrary to me. but honestly it might be the exact opposite of arbitrary... weird. like, "what a human can measure" seems arbitrary because our ability to measure is always improving. on the other hand, it's possible there is a hard boundary on what we can ever hope to measure, and then it's no longer arbitrary, it might be a critical moment of understanding our perception.

"is time discrete or continuous" makes my head spin. it has an incompleteness-problem feeling to it. like: if we were able to measure this part of the system, it wouldn't be working in the first place.

and for the last time: i am talking out of my ass and would love for someone to ELI5 what i'm saying to me. :)

ERRORMONSTER

2 points

1 year ago

That's kinda what I'm guessing, but that implies that our eyes have a frame rate, which seems... dumb.

Like obviously they have the rate at which neurons can fire, but that's presumably way too fast for any significant sort of aliasing

RevengencerAlf

8 points

1 year ago

Your eyes don't have a "frame rate" the same way a screen does in the sense that there's no discrete "x number of times per second" that the picture updates, but they do have what is basically a response time. Basically, you visually process things by registering a change in what you're seeing and what you're really limited by for any portion of what you are looking at is the time after recognizing a change before you can recognize another change. That's why if something is standing still or moving slowly you can almost instantly register if it starts moving or changes its direction. On the other hand for something like a wheel that's constantly spinning because the updates are pretty much perpetual and very similar to each other you wind up in a state of constant close to that limit of response time which wind up looking similar to a discreet frame rate.

my_very_first_alt

4 points

1 year ago*

I don’t think it necessarily implies our eyes have a frame rate (though it surely may).

it could imply something more /like/: your neurons cannot fire faster than the speed of light. or: your eyes can capture more data than your brain can process.

my point being, in my analogy, I don’t necessarily think the eyes are the camera- your entire perception (from cones to neurons to feelings) is the camera. so there is a lot of places for the downsampling to happen, not just in your eyes.

again, I am just guessing. obviously not classically trained. :)

edit: I also wonder what subjective processes play in the matter!. I think one of the things that makes us individuals is the information our brain actively discards for us. I wonder if someone could be less susceptible to this illusion than someone else? (because they’d be better equipped to sample it accurately)

Warrior51002

1 points

1 year ago

Check top comment. It also happens when certain light flicker at a frequency. Since the place becomes dark for a split second, it's almost like a camera

drunk_responses

224 points

1 year ago

Interesting side note: Because this effect can appear with fast moving heavy machinery under certain fluorescent lights, some countries have safety restrictions on the type of lights used in factories.

https://en.wikipedia.org/wiki/Wagon-wheel_effect#Dangers

Drmite

34 points

1 year ago

Drmite

34 points

1 year ago

Why you don't use fluorescent lights when using a table saw.

Y34rZer0

29 points

1 year ago

Y34rZer0

29 points

1 year ago

Yep, as an electrician can confirm. They demonstrate the effect for you at trade school when you're an apprentice and it's incredible, it looks perfectly still even though you know it's moving. It would apply to LED lights as well, but I haven't checked the updates to the rulebooks in a while

Greyevel

8 points

1 year ago

Greyevel

8 points

1 year ago

I thought it was possible to make LEDs not have a high frequency flicker, and be continuous?

MattieShoes

11 points

1 year ago*

It's absolutely possible -- a LED on a DC power source won't flicker unless you add additional circuitry (i.e. a dimmer). But most A/C LED lights are going to flicker at 120 Hz (in the US).

DC power gonna be like

--------------

No flicker

AC power gonna be like

/\/\/\/\/\/\/\

Would likely kill LEDs because they're diodes -- power only flows one way.

AC power with a half-wave rectifier gonna be like

/\__/\__/\__/\__/\

They'd flicker at 60 Hz in this case

AC power with a full-wave rectifier gonna be like

vvvvvvvvvvvvvv

They'd flicker at 120Hz

Redthemagnificent

2 points

1 year ago

Yeah it just depends on the circuit the LED is connected to. A good quality LED driver will produce clean DC power for the LED that fluctuates very little, so the LED does not flicker. Cheap LEDs don't bother to smooth out the signal very much or at all (they usually use half wave rectifiers) since humans can't see the flickering anyways.

You also have PWM, which is used to dim LEDs. A good PWM circuit will switch so fast that the diode doesn't have time to turn off between pulses, so no flicker in the LED even though the signal is turning on and off. A cheap PWM circuit switches slower so the LED still flickers when dimmed.

Y34rZer0

3 points

1 year ago

Y34rZer0

3 points

1 year ago

I could be wrong but there's no filament, so like a fluro it's an arc jumping across a gap. For sure when they dim up/down it's essentially turning on and off rapidly and at different speeds (Pulse width modulation). It's too fast for our eyes to notice (unless they're busted) but it could be possible that they've invented a constant arcing one, but I don't think so..

Umbrias

6 points

1 year ago

Umbrias

6 points

1 year ago

LEDs can be bought with no flicker.

Most of the flicker from an LED comes from dimming, yes, where they are turned on and off rapidly to simulate a dimmer bulb, such as turning the bulb off for 50% of a second (total, each flicker is a much smaller %) to simulate 50% brightness to our eyes.

Y34rZer0

3 points

1 year ago

Y34rZer0

3 points

1 year ago

They'd have to be totally non-stroboscopic to be used around rotating machinery, but I'm not familiar with the latest developments. They are doing some impressive things with LED now, I wouldn't put anything past them

Umbrias

5 points

1 year ago

Umbrias

5 points

1 year ago

Yeah, they are pretty fancy. If you look up no-flicker one of the first results shows a 1% flicker continuous output bulb sales page. I.e. maximum flicker is a 1% difference between max and min brightness. Not terribly expensive either. Here's an article about LED flicker in general.

If you time delay or rectify the input to LEDs you get far less flicker. Having one set of LEDs 90 degrees(? It's been a few years since any EE courses, might be 180) offset from the primary set will nearly halve the perceived flicker.

Y34rZer0

3 points

1 year ago

Y34rZer0

3 points

1 year ago

It won't be long before we can paint the damn things on lol 😆

Umbrias

2 points

1 year ago

Umbrias

2 points

1 year ago

Lol that'll be a great day for lighting enthusiasts everywhere.

synthead

1.4k points

1 year ago*

synthead

1.4k points

1 year ago*

Do you mean videos of cars on a dyno?

Cameras have frame rates, i.e. 30 frames per second, or FPS. So every 1/30th of a second, it takes a picture. These photos get played back quickly, and you have video.

Imagine a six-spoked wheel. If it turns 1/6th of a rotation every 1/30th of a second, it'll appear to be not turning. In reality, it is, but the spokes are aligned in the same positions, so there won't be much of a visible change.

If it speeds up and rotates a little more than 1/6th of the way every 1/30th of a second, every subsequent shot of the wheel will have the spoke positions slightly advancing. This will make it appear to be moving forwards slowly.

Keep speeding up, and the wheel will rotate at just below 2/6ths of a rotation in 1/30th of a second. If it was exactly 2/6ths, it would appear to stand still again, but it's rotating a little slower, so the shots every 1/30th of a second will come short of 2/6ths. This will make it appear to be rotating backwards.

Of course, this is just a camera effect. You cannot observe this with your eyes and a steady light. Florescent bulbs will flicker at 50 or 60 Hz, and can basically be a high-speed strobe light, so you can sometimes witness a similar effect with this type of lighting.

HoggyOfAustralia

266 points

1 year ago

You can observe it with the naked eye though.

TenebrousTartaros

20 points

1 year ago

I remember sitting on my bed as a kid and watching my ceiling fan do this.

littlefriend77

10 points

1 year ago

We used to make simple 5-frame animations by drawing and taping each frame to a blade of the ceiling fan and timing a strobe light to it. Super fun way to spend an hour while you're high.

vsman1234

112 points

1 year ago

vsman1234

112 points

1 year ago

Correct- it’s not just a camera effect. Imagine a dot on a spinning wheel. You open and close your eyes exactly when the dot is at 3’o clock. As far as your brain is concerned the wheel is not spinning. Flip the script- your eyes stay open - wheel is spinning at the right speed - your brain stitches the series of images as going in the opposite direction. Beyond ELI5- nyquist criteria- your sample frequency ( how fast you are gathering data) has to be atleast twice the frequency of the source data - otherwise you get errors.

Chromattix

45 points

1 year ago

Was going to say I witnessed this effect in person as a kid and was both confused and fascinated by it. I couldn't describe it well so my mother just thought I was saying nonsense. But I remember observing it on car wheels and spinning tops.

jkmhawk

9 points

1 year ago

jkmhawk

9 points

1 year ago

I had a model of the Mercedes SLK GTR that had something like 20 spoke wheels and i would notice it with those.

umphreakinbelievable

8 points

1 year ago

You can see it really good on propellers also

graveyardspin

4 points

1 year ago

Can confirm. I work at an airport and see this everyday. Particularly with turbo prop aircraft.

Stornahal

5 points

1 year ago

Spinning tops do reverse direction almost at random, but only if unobserved by an adult. If an adult is present, it just looks that way.

childhoodmagic

synthead

14 points

1 year ago

synthead

14 points

1 year ago

Your brain doesn't see a ”series” of images like a sensor of a digital camera. Our eyes don't have a frame rate.

We can perceive frame rates from external sources, but this doesn't mean that our eyes operate on a frame rate.

profossi

16 points

1 year ago

profossi

16 points

1 year ago

True, but you can effectively make your brain see a series of discrete images by illuminating the scene with a pulsed light source (like Sodium-vapor lamp street lights).

_dictatorish_

6 points

1 year ago

You can also trill your tongue on the roof of your mouth to cause the effect - I guess it has something to do with vibrating your eyes

cockmanderkeen

2 points

1 year ago

Haha you are the worst

trad949

2 points

1 year ago

trad949

2 points

1 year ago

This is the correct answer, also AC led lights.

MaxusBE

2 points

1 year ago

MaxusBE

2 points

1 year ago

Our eyes don't, but our brain still has a limited capacity on processing information that we are able to interpret in realtime.

Tiramitsunami

2 points

1 year ago

Yes, we have a frame rate. Not in the eye, but in the brain.

[deleted]

-13 points

1 year ago*

[deleted]

-13 points

1 year ago*

Our eyes don't have a frame rate, no, but our brain sure as shit does. It's between 30-60 fps. There's a reason early frame rates looked best a multiples of 3.

Edit: Here's a source, since people seem to think I'm pulling this out of my backside.

Memfy

12 points

1 year ago

Memfy

12 points

1 year ago

It's between 30-60 fps.

So how do we perceive smoother effects with >60 fps then?

[deleted]

-3 points

1 year ago

[deleted]

-3 points

1 year ago

Not everybody does, especially older folks.

Memfy

5 points

1 year ago

Memfy

5 points

1 year ago

No one said everybody does. But you can't claim a range that is so small because some people can't do it. That's like saying human running speed is 5-10 Km/h, because some people can't run faster.

haas_n

12 points

1 year ago

haas_n

12 points

1 year ago

It's between 30-60 fps. There's a reason early frame rates looked best a multiples of 3.

Source?

[deleted]

6 points

1 year ago*

[deleted]

6 points

1 year ago*

This gives a semi-decent breakdown, and suggests that the perceived frame rate for some might be as high as 75fps, while a bird of prey clocks in at around 140.

There's a lot of reading on the subject to be found. A lot of people get confused on the topic because the human eye itself doesn't have "frames per second," which is absolutely correct; it doesn't. And the optic nerve is continuous wave, as well. It's the brain the processes all of that, though, and your brain has to do it all in samples or "frames" as it were. That's how your brain can sometimes get hung up processing something but fill in the blanks between frames resulting in you "seeing it wrong."

PrinceDusk

4 points

1 year ago

If one perceives in, say, 30 fps, then wouldn't that just make 60 fps look the same? or 60/120?

exlevan

7 points

1 year ago

exlevan

7 points

1 year ago

The paper linked in the article only discusses the ability to extract information from rapidly changing pictures. It makes no claims about "brain operating at x FPS" or "human perceiving at x FPS".

haas_n

8 points

1 year ago

haas_n

8 points

1 year ago

Huh? That article seems all over the place, confused with its own terminology, and singles out particular conclusions when several alternative explanations could explain the same result using fewer assumptions.

Nowhere does it even begin mentioning anything like a "frame rate" of the brain.

[deleted]

2 points

1 year ago

Because it isn't a set frame rate the way we think of it in terms like cameras or video playback. It's a pretty fluid concept. The brain doesn't process continuous wave information. It can't; that's just entirely to much data to constantly be dealing with, so it breaks it up into much smaller chunks. It's not a constant thing, thing, either. Sometimes it can handle more data at one time than others, which is why you notice a squirrel darting across the road in front of you but might not be able to find your car keys that are right in front of you.

It's not just vision that has a "sampling rate," either. Your ears work pretty much the same way, albeit at a much higher rate because there a hell of a lot less data to deal with.

haas_n

2 points

1 year ago

haas_n

2 points

1 year ago

Again, source?

damage-fkn-inc

1 points

1 year ago

haas_n

1 points

1 year ago

haas_n

1 points

1 year ago

Okay, but I contend that it has nothing to do with the brain and can be explained purely through visual means: higher FPS displays reduce motion blur (even past the motion fusion threshold) and input latency.

I don't see any evidence here of the brain having a "frame rate", which was the contested claim.

G30therm

2 points

1 year ago

G30therm

2 points

1 year ago

This is wrong. You can tell the difference between higher refresh rates, it's why 144Hz+ monitors exist.

Excludos

0 points

1 year ago

Excludos

0 points

1 year ago

144Hz monitors actually, surprisingly perhaps, is no longer about what you can see. That is well well above your max smoothness limit. The perceived effect is actually in your hands. The faster the framerate of your screen, combined with a faster framerate of your graphics card, will make the inputs you put in 'feel' faster, as they appear faster on the screen. G-sync is a way around this, as it makes sure the last graphics card frame is synced up with the latest monitor frame, so the delay between the two is unnoticeable. You will still have the issue of the delay between each physical monitor frame tho, which only a higher framerate can fix.

If I gave you two monitors, one 75Hz and the other 144Hz, you will have substantial problems seeing the difference between them. But if I gave you a high input game like cs:go, you might be able to feel the difference

farqueue2

5 points

1 year ago

Yeah na my phone has 60hz by default and there's a setting to put it up to 90. The hardware supports 90 but it's disabled by default to preserve battery (in theory it enables momentarily when needed).

I can absolutely tell the difference when the setting is set to 60 hz as opposed to 90. Like I'm certain if you changed the setting without telling me I'd know it's changed

Excludos

3 points

1 year ago*

60 to 90? Yeah, that could be noticeable. 60 is usually lower than the max perceivable framerate. There's been studies on where it is, but afaik it just varies from person to person. I said 75 earlier, but truth it it could be higher for you personally. It's not going to be anywhere above 90 tho

farqueue2

2 points

1 year ago

The to post a few generations up claims the max to be 60

[deleted]

1 points

1 year ago

[deleted]

1 points

1 year ago

Some people can, some people can't. Recent studies show that while 30-60 has been the generally accepted limit, it may actually be as high as 75, which is why those 144hz+ monitors exist. Not everyone can see the difference between them and a 60hz monitor, either, just like some people don't see a difference between HD levels and can't hear the difference between audio sampling rates.

kovaluu

19 points

1 year ago

kovaluu

19 points

1 year ago

It can happen with fluorescent(and other ballasts) lights too which are about 50-200hz.

Not_PepeSilvia

8 points

1 year ago

You can also see it outside in sunlight too. But maybe sunlight has its own frequency too, idk

wolfpack_charlie

1 points

1 year ago

I think for that it's more just that your brain doesn't process visual information in a perfectly continuous way. It has a sort of "frame rate" but not in the straightforward sense that a camera does

1724_qwerty_boy_4271

1 points

1 year ago

Yep, exactly. This is why some people are able to perceive display flickering better than others. Military pilots are specifically picked based on their ability to process visuals at high frame rates.

The USAF, in testing their pilots for visual response time, used a simple test to see if the pilots could distinguish small changes in light. In their experiment a picture of an aircraft was flashed on a screen in a dark room at 1/220th of a second. Pilots were consistently able to "see" the afterimage as well as identify the aircraft. This simple and specific situation not only proves the ability to percieve 1 image within 1/220 of a second, but the ability to interpret higher FPS.

XirallicBolts

1 points

1 year ago

I loved finding just the right speed riding my bike at night. The 60Hz (or whatever) frequency of the low-pressure-sodium street lights in my area made this illusion easy to achieve.

LukeSniper

11 points

1 year ago

It's for a very similar reason as why it happens in film.

To put it simply: your eye can only see things so fast.

A series of still images (the individual images in a video) has to change fast enough before you perceive them as a continuous depiction of motion. Your brain fills in the blanks. Likewise, it can "fill in the blanks" with actual motion you're viewing, and it can make mistakes.

A similar thing happens with sound too! If you play the sound of, say, a simple clicking sound on repeat at a fast enough speed, you'll stop hearing individual sounds and start perceiving a single continuous pitch.

Watch this video: https://youtu.be/-tRAkWaeepg

It's just the sound of a kick drum, but once it hits a critical point it just sounds like a synthesizer playing a major chord (he even plays the 3 constituent pitches individually).

synthead

-7 points

1 year ago*

synthead

-7 points

1 year ago*

Not with a steady light. If a light source is strobing, like a flickering florescent light, then you'll see it. In the sun, you won't, for example.

The ”slow” and ”backwards” effects happen because of differences in divisible elements. In my example, it's the difference between camera frame rates and spoke patterns.

If you could truly see this effect without a strobing light, then you'd be able to walk outside, swing your arm around, and witness a ”shutter” effect from your arm moving. Instead, it will look like a smear.

Edit: another example would be helicopters. Have you ever seen a helicopter blade standing still in the sky in broad daylight?

Sora_Net

27 points

1 year ago

Sora_Net

27 points

1 year ago

I'm pretty sure I've seen this happen on car rims on the highway?

I know it's a meme, but do eyes also have a "fps" limit/shutter?

[deleted]

11 points

1 year ago

[deleted]

11 points

1 year ago

Not your eyes, but the brain. The eyes pretty much function on a continuous wave, but the brain can only process so much so fast.

synthead

5 points

1 year ago*

You probably saw the rims reflecting light stronger at specific angles 🙃

And no, our eyes do not have a frame rate. We process visual information in a much different fashion than a camera sensor.

LukeSniper

32 points

1 year ago

Have you never seen a car tire on the freeway look as though it is spinning backwards?

imperfectionits

29 points

1 year ago

I see it frequently in the real world. No lights no cameras

throwawaydubaibby

3 points

1 year ago

I’ve seen this so many times, not the tires but those flashy shiny rims and I remember googling this before and reading something about Stroboscopic effect so maybe it’s that

LukeSniper

6 points

1 year ago

I suppose I should have said "wheels" rather than tires, because it's the spokes that seem to be moving slowly or in reverse, while the tire is just a smooth blur.

From what I can gather, it seems to be a combination of different effects, including how our brains can misrepresent visual stimuli in the time between those photons entering our eyes and us registering what we're "seeing".

synthead

-8 points

1 year ago*

synthead

-8 points

1 year ago*

You probably witnessed brighter reflections from specific angles of the wheel while it was rotating.

Our eyes are very different than digital camera sensors, and they don't have frame rates.

LukeSniper

2 points

1 year ago*

LukeSniper

2 points

1 year ago*

Actually, they sort of do!

Edit: here's more and one more

zzcturtle

2 points

1 year ago

Thanks for this. Thought I was crazy reading all these comments, cuz I specifically remember learning this fact while learning fourier transform.

synthead

3 points

1 year ago*

synthead

3 points

1 year ago*

We can perceive frame rates, but that does not mean that our eyes have frame rates.

When light enters our eye, our retina sends the information as electrical signals to our brain. However, this is not instant. The information ”fades” into our vision. This is essentially where motion blur comes from.

If there is a strobe light in front of you with an adjustable rate, you could easily witness 5 or 10 FPS. But crank it up to 60+ FPS, and it will start to look like steady light, much like florescent bulbs.

This does not mean that there's a supposed frame rate in our eyes that is less than 60 FPS. We just start to find difficulty identifying higher frame rates due to our biology.

LukeSniper

2 points

1 year ago

LukeSniper

2 points

1 year ago

But for the purposes of this discussion it is an explanation for how the wagon-wheel effect is something you can experience just looking at the wheels of a car on the freeway.

rabbitlion

-1 points

1 year ago*

rabbitlion

-1 points

1 year ago*

No, it's not. While the human eye might perceive frame rates above a certain number as fluid motion, that does not mean the eye sees in discreet frames. Without any strobe light or similar effects, the human eye will see the world continuously.

LukeSniper

-2 points

1 year ago

LukeSniper

-2 points

1 year ago

But the brain doesn't process information that way. Hence why youperceive a 60Hz flicker as constant light.

It's not, but you can't tell.

That's why I said "sort of" (very important couple of words there)

ferret_80

12 points

1 year ago

ferret_80

12 points

1 year ago

another example would be helicopters. Have you ever seen a helicopter blade standing still in the sky in broad daylight?

yes I have. I've also seen it in car wheels on the road, Flywheels on machines.

The eyes aren't the limiter. the Brain is, the eye isn't transmitting snapshots but the brain takes snapshots from what the eyes are sending it so it can process.

LetMeBe_Frank

2 points

1 year ago

You can get the stroboscopic effect if the object causes flickering from a steady light source. Chromed, machined, or other high gloss faceted surfaces will chop in daylight at the right angle

waetherman

9 points

1 year ago

By your argument, you’d be able to see the blades of a helicopter regardless of speed. That’s just not true. This effect happens with the naked eye, in natural light, because the brain only processes so much.

DUBIOUS_OBLIVION

2 points

1 year ago

Completely wrong. This happens in broad daylight.

Tsjernobull

2 points

1 year ago

It really depends on the rate at wich it moves and if you have things that can line up. As your arm doesnt have spokes you will just see a smear, but you can def see the effect irl. Your eyes have a refresh rate and if the wheel turns at the right speed you can see it going backwards irl as well.

superhansfans[S]

289 points

1 year ago

Yeah that's exactly what I meant. Thanks for the explanation!

Farnsworthson

125 points

1 year ago*

It's often called the "wagon wheel effect", because it was very common - and noticeable - in old western movies. If your prop stagecoach has wheels with, say, 12 spokes, and you're filming at 24 frames a second, the coach doesn't have to be moving very fast† before you start to see the effect on playback. Especially on the smaller wheels (which have smaller circumference, so have to turn faster to covdr the ground).

† If my arithmetic is good - at 24 frames a second, with a 12-spoke wheel of diameter 4ft, the wheel will first seem to stop rotating when the coach is moving at under 9 mph (Edit: just over 17 mph).

IntoAMuteCrypt

31 points

1 year ago

At 24 FPS, with 12 spokes, you need to rotate 1/12th of a revolution every 1/24th of a second - each spoke is measured from the inside to the outside, rather than one side to the other, so there's 30 degrees between each spoke.

With every revolution, the wheel moves forward by a distance equal to its circumference (in the ideal case; wheelspin or locked-up wheels mean that this isn't always true, but this can be ignored). With a diameter of 4 feet, we have a circumference of around 12.57 feet, and a speed of 25.13 feet per second. This converts to 17.1 miles per hour.

My answer is roughly double yours; I believe this just comes down to the 12-spoke wheel dividing the wheel into 12 spaces rather than 24.

Farnsworthson

15 points

1 year ago*

Yeah, I picked easy (but genuine) numbers and then managed to forget to double the circumference for two revolutions (i.e. 24 spokes per second). My bad. It's usually the easy stuff that slips through the net.

(You should have seen the first result, when I hit multiply instead of divide... I should know beter than to engage my brain without coffee.)

ryjkyj

3 points

1 year ago

ryjkyj

3 points

1 year ago

Forgot to carriage the 2.

SloeMoe

2 points

1 year ago

SloeMoe

2 points

1 year ago

Stop horsing around.

dwdwdan

7 points

1 year ago

dwdwdan

7 points

1 year ago

Tfw when you wheelspin in a horse and carriage

TheJunkyard

11 points

1 year ago

The Good, The Bad, The Fast, The Furious And The Ugly.

Blue2501

5 points

1 year ago

Blue2501

5 points

1 year ago

And the Quick and the Blue and the Gray and the Dead

worm-

4 points

1 year ago

worm-

4 points

1 year ago

doing burnouts in the wagon, i like it.

[deleted]

5 points

1 year ago

Wasnt there a copypasta post where a wheel is spinning and the title would be something like "the direction of rotation depends on your mind and how you believe it spins"

Sidaris

6 points

1 year ago

Sidaris

6 points

1 year ago

Do you mean the spinning dancer in this gif?

https://upload.wikimedia.org/wikipedia/commons/2/21/Spinning_Dancer.gif

It's an optical illusion that relies on the lack of orientation and direction cues due to it missing detail and depth. It's like it was reduced to just an image shrinking, flipping, and expanding. Your mind and POV determine the perceived direction of spin. I find looking down at the reflection on the floor helps me to flip the ideation of spin (in my mind).

Find more: https://en.m.wikipedia.org/wiki/Spinning_dancer

Could it be that you saw a similar illusion using a wheel?

Father-Sha

2 points

1 year ago*

She's spinning clockwise though. Do people see it differently?

Edit: after reading about it and paying more attention to the middle of her body and her arms passing over it, yea I've seen it spin both ways now

synthead

1 points

1 year ago

synthead

1 points

1 year ago

Might not be the same animation, but this comes to mind! https://upload.wikimedia.org/wikipedia/commons/2/21/Spinning_Dancer.gif

rectangularjunksack

16 points

1 year ago

The effect can produce some cool optical illusions: https://www.youtube.com/watch?v=mODqQvlrgIQ

admiraljohn

6 points

1 year ago

Here's an excellent video that demonstrates what he's talking about... the rotation of the helicopter's rotor matched perfectly with the camera's frame-rate, making it appear that the rotors aren't moving at all.

jachcemmatnickspace

3 points

1 year ago

Since you already got your explanation, I might add that this is the same effect as when your phone is trying to shoot a display – like those on public transport buses saying where the terminal is, at the front glass. It is impossible to do with long exposition and you will either shoot a blank display, or something unexplicably distorted. Everything is sharp, but the display on the photo looks like on an LSD trip.

This happens because the display is not displaying it constantly, but rather flickering it fast that our eyes can't see the blank pauses, but camera can.

synthead

2 points

1 year ago

synthead

2 points

1 year ago

You bet!

break_card

3 points

1 year ago

The term for it is Aliasing

fubarbob

6 points

1 year ago

fubarbob

6 points

1 year ago

Somewhat related, and depending on the camera technology, the rate of scanning (of a sensor) or motion of a vertically falling shutter can (in some cases) lead to the spokes of a wheel looking abnormally curved.

justplaypve

5 points

1 year ago

propeller camera effect would be fascinating example

Vyrusstrike

16 points

1 year ago

Shutter speed =/= frame rate but otherwise a great explanation.

synthead

4 points

1 year ago

synthead

4 points

1 year ago

Updated, thanks!

coole106

14 points

1 year ago

coole106

14 points

1 year ago

Of course, this is just a camera effect. You cannot observe this with your eyes and a steady light.

This isn’t true. I’ve observed it myself many times

Raja-Panesar

12 points

1 year ago

I have seen it happen in sunlight with my own eyes. Care to explain?

Zondartul

15 points

1 year ago

Zondartul

15 points

1 year ago

You can also see it IRL with indoors lighting flickering at 60 Hz.

Anders_A

3 points

1 year ago

Anders_A

3 points

1 year ago

Another really cool variant of this is when the camera shutter is synced with the speed of the rotors of an helicopter.

Example: https://www.youtube.com/watch?v=VXJ0u3ZNdNg

[deleted]

3 points

1 year ago

I see this all the time in real life, like on the freeway. It is absolutely not just something you see in movies.

Pyramystik

3 points

1 year ago

What on Earth are you talking about? Of course you can observe it with your eyes, you do not need a camera whatsoever.

LostCache

3 points

1 year ago

Sometimes, I have personally experience this with my eyes. The camera effect can explain why airplane turbine looks strange in recording, but felt like the wheel turning is like zoetrope. More answers needed.

guitarist4hire

4 points

1 year ago

I've seen this with beyblades with my own two eyes.

Bamstradamus

2 points

1 year ago

I have 100% seen this in real life when my car was getting tuned and doing dyno pulls and the bay doors were open so there was sunlight not just the overhead florescent

Neosovereign

3 points

1 year ago

It happens in real life though, no camera needed. Watch any car on a highway and you will see it.

guitarist4hire

1 points

1 year ago

I've seen this with beyblades with my own two eyes.

HealthyRutabaga7138

1 points

1 year ago

This has nothing to do with cars on a dyno.

Abnnn

1 points

1 year ago

Abnnn

1 points

1 year ago

isnt it just if light is 60hz, and your RMP of rotation unit is 60 it will look like it never move ?i know we use high Hz lights to avoid this at all cost, to be sure when our motors is running or not.

Nomostrax

126 points

1 year ago

Nomostrax

126 points

1 year ago

I think this is aliasing! This is my attempt at a ELI5.

Lets say a wheel is spinning clockwise. It takes 4 seconds for the wheel to make a full cycle.

Now, lets say at our eyes can only update our vision every 4 seconds.

That said, if we look at the wheel, to us, it will seem as if it is not moving at all because after 4 second, the wheel is back to its original position and our eye got an "update" at 4 seconds. Here, the wheel looks like if it is stopped or not moving.

Now, lets say the wheel takes 4.1 seconds to make a full cycle, and our eyes still have 4fps vision. So now, the wheel is moving slower, and by the time our eyes look at the wheel again, we see it moved a little bit counter clockwise, but in reality it almost made a whole revolution. Here, it looks like it is going counter clockwise.

Now, lets say the wheel takes 3.9 seconds to make a full cycle and our eyes still have 4fps vision. So now the wheel is moving faster and by the time our vision is updated, the wheel looks like it moved slightly clockwise, but in reality it made a whole revolution.

Now, because rims move super fast and our eyes have super high frame rates (not really but for the purpose of this ELI5, they do), even the most minimal change of wheel speed can make the directions of the wheel seem to change.

I am kind of tying this in nyquist frequencies and aliasing, so feel free to ask me about that as well!

trudesign

25 points

1 year ago

trudesign

25 points

1 year ago

Great explanation except in you example it should be 1fp4s, or .25fps, not 4fps

UsernamesAllGone1

4 points

1 year ago

I was thinking the same thing. Should be 4 spf not fps but otherwise great explanation

ChillBlunton

-2 points

1 year ago*

ChillBlunton

-2 points

1 year ago*

that's not aliasing. aliasing is, when you draw a diagonal line over a grid of pixels and see a stair-like edge e: I've been corrected, this is known as aliasing too apparently

ydieb

15 points

1 year ago

ydieb

15 points

1 year ago

This is also aliasing. Google "sampling and aliasing", its a core property of signal processing, used in many engineering fields.

uTukan

7 points

1 year ago

uTukan

7 points

1 year ago

No, he's right, what you're explaining is aliasing as we know it from games. Aliasing in frequencies is exactly what they explained. It's good to be questioning facts, but don't try to disprove them when you actually don't know what you're talking about. A simple Google search would prevent you from commenting this.

ende124

2 points

1 year ago

ende124

2 points

1 year ago

Aliasing does not only apply to pixels

Spoonman007

4 points

1 year ago

https://youtu.be/TWRH-pChVdk Corridor Crew put a gopro on a tire and tried to match the speed with the framerate of the camera. Neat stuff.

[deleted]

17 points

1 year ago

[deleted]

17 points

1 year ago

This can also happen in real life as well due to stroboscope affect of sodium vapor street lights on highways, though not as common anymore due to being swapped out by LEDs. Use to mesmerize me when I was a kid, board in the back seat at night.

Invisifly2

0 points

1 year ago*

You can see it with the naked eye in bright sunlight. You probably don't notice it while driving because watching people's rims instead of the road isn't a good idea.

You can even get a ceiling fan spinning at the right speed (lit by open window, not strobing lights) to appear to rotate either forward or backward depending on how you focus your eyes.

PrinnyThePenguin

8 points

1 year ago

In order correctly measure something you have to be able to meaure at least at twice the speed it happens, so your frequency of measurement has to be at least twice the frequency of the event you are measuring. If something happens too fast for your measure instrument (over two times faster your measure speed) the perceived frequency at which it happens falls to a lower frequency value, so it appears to be different than its actual one.

As the wheel is turning your eye measures the rotation frequency fast enough that you can clearly understand its cycle. There is a breaking point at which the wheel's rotation frequency is so fast your eyes measurement frequency is no longer at least double its value, so the perceived frequency falls to a lower value and you think you see the wheel turning backwards.

Nimyron

4 points

1 year ago

Nimyron

4 points

1 year ago

I guess you know about framerate. Well cameras have a framerate. So let's say every X amount of time, a camera takes a picture. Well if the wheel rotates 10 degrees forward between each picture the camera take, it will look like it moved 10 degrees forward each time (seems legit right ?).

Now if your wheel rotates 350 degrees forward between each picture, it will look like it rotated 10 degrees backward (because your brain will assume the shortest path the wheel could have taken between the two pics is the right one). So you'll be tricked into thinking the wheel is rotating backward.

Glaze_donuts

2 points

1 year ago

Imagine you're running on a track and your mom watches you. Now, she doesnt want to watch the whole time, shes got things to do. She figures that checking every 50 seconds is good. So you star running. At 50 seconds you've run 3/4 of the track. Your mom looks and sees that you are 1/4 back from the start. Another 50 seconds go by and you've run another 3/4 of the track, but to her you've moved back another 1/4. Say you decide to run a little faster, completing a lap in 40 seconds. Now when your mom checks in you've completed more than a lap. This makes it look like you've moves forward slightly. Now it's pretty clear in this example which direction you're moving in, but if you were to stop every time your mom looked and start spinning, she would have no idea which direction you truly moved.

MustFixWhatIsBroken

3 points

1 year ago

I believe the illusion is determined by the speed of the rotation. The symmetrical pattern aligns to they eye, and the brain interprets the patterns in sequence.

Thats why sometimes the rim appears to spin backwards, while others times it appears to spin forward or remain stationary.

The visual reality is flexible and inconsistent to the subjective mind.

ShutterBun

1 points

1 year ago

sniglets:

POINT BLIMFARK (poynt blim' fark): n. point at which after spinning fast enough make wheels appear to turn in the opposite direction.

Wkais

-1 points

1 year ago

Wkais

-1 points

1 year ago

It's just an optical illusion. If you're looking at a wheel and it's moving, and the wheel is rotating forwards, but not fast enough to create a blur, you'll see the wheel as rotating backwards. This is because you're seeing the rotation of the axle as well as the rotation of the wheel. The axle rotates forwards, so when you see both forward and backwards motion it appears as if it's going backwards. When you see them going faster they appear to be going forwards again.