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How a TV Works in Slow Motion

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Subido el 10 de diciembre de 2018 por Antonio S.

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Hello there, my name's Gavin, 00:00:00

and welcome to this episode of The Slow Mo Guys, 00:00:01

very oddly presented from my living room. 00:00:03

A while ago, I made a video called 00:00:06

how a camera works in slow-mo, 00:00:07

and the response was great. 00:00:09

So I thought a good natural progression to that video 00:00:11

would be how a TV works in slow-mo. 00:00:13

This is an 85-inch LCD TV, 00:00:16

and whenever I'm playing something on it 00:00:18

or watching something on it, 00:00:20

my eyes and brain are being misled and tricked, 00:00:22

giving me the illusion of watching a moving object, 00:00:25

when in fact, I'm just watching several still images 00:00:28

just shown to me very, very fast. 00:00:31

If I'm watching a film, 00:00:33

I'm being shown 24 images every second. 00:00:34

And to my eyes, 00:00:37

that looks like I'm looking at a moving object, 00:00:38

when in fact, I'm looking at 24 individual pictures. 00:00:40

If I'm playing a game, 00:00:43

it's the same except maybe 30 to 60 frames a second. 00:00:44

And if I'm on a PC, it could be hundreds. 00:00:48

PC master race. 00:00:50

But a TV like this is actually incapable 00:00:51

of showing you one image 00:00:54

and then a 24th of a second later, 00:00:55

just switching all at once to the next image. 00:00:57

And to illustrate this next point, 00:00:59

I'm gonna use a very old and very crap CRT TV. 00:01:01

That stands for cathode ray tube. 00:01:06

If you've ever seen one of these filmed, 00:01:08

you may notice that it looks slightly different 00:01:10

on camera than it does to your eye. 00:01:12

Look at that. 00:01:16

The reason it looks like this is because 00:01:17

the shutter speed of this camera is out of sync 00:01:19

with the refresh rate of this screen. 00:01:22

The frame is constructed from the top 00:01:25

to the bottom multiple times per second. 00:01:27

That's 60 times in the US, 60 hertz. 00:01:30

I've prepared for you some high speed footage 00:01:32

that I shot a long time ago on the V2511 00:01:34

of this screen and this screen and some others. 00:01:36

A lot of it is Dan playing Super Mario 00:01:40

on the NES extremely badly. 00:01:42

Here's the TV and the cat played back at 25. 00:01:44

This is how it would be perceived in real time. 00:01:46

And now at 1600 frames a second, 00:01:48

you can actually see the scan line 00:01:50

moving from the top to the bottom. 00:01:52

You'll notice that on a CRT screen, 00:01:53

It's only the active line of pixels that's bright 00:01:56

and your persistence of vision will actually build that 00:01:59

into a complete image. 00:02:01

It's messing with my eyes, this. 00:02:03

Triff, it's like a dance floor. 00:02:06

Oh, didn't even make it past the first guy. 00:02:13

Slowed all the way down to 2,500 frames a second, 00:02:19

you can now differentiate each individual frame 00:02:22

being built from top to bottom. 00:02:25

It takes an extremely fast camera to see that each frame 00:02:33

is built line by line from top to bottom. 00:02:36

But it takes an even faster camera 00:02:38

to see that each line is drawn from left to right. 00:02:41

Slowed down to 28,500 frames a second. 00:02:45

We're now seeing glimpses of that, 00:02:47

but we do need to go even slower. 00:02:49

This is now 118,000 frames a second. 00:02:52

I'm gonna put the stats up for you here 00:02:55

so you can see the actual amount of time that it took. 00:02:57

And you can see now that the line is being drawn 00:02:59

from left to right on the screen. 00:03:02

Now at 146,000 frames a second. 00:03:04

To gain perspective on just how slow this actually is, 00:03:07

you can see the exact time I shot this. 00:03:10

So this is hours, it was just past midnight, 00:03:13

23 minutes, 41 seconds. 00:03:15

This is a tenth of a second, a hundredth of a second, 00:03:18

one thousandth of a second, or a millisecond. 00:03:21

And then over here, you've got a 10,000th of a second, 00:03:23

a hundred thousandth of a second, 00:03:26

and this unit here is the millionth of a second, 00:03:28

or a microsecond. 00:03:31

We are now at 380,000 frames a second 00:03:33

as our recording frame rate. 00:03:36

That is the highest frame rate we've ever shot 00:03:37

so far on this channel. 00:03:40

And using this information, here's a little bonus fact. 00:03:41

A CRT screen can draw Mario's mustache 00:03:44

in less than a 380,000th of a second. 00:03:48

That is some seriously fast spatial here. 00:03:53

And if you're wondering why this footage 00:03:56

looks extremely mucky and blurry, 00:03:57

is because the resolution is only 256 by 128, 00:03:59

which plonked into a 4K frame is this big. 00:04:03

That CRT screen is standard def. 00:04:07

This is a 4K screen, 00:04:10

which means it's 3840 by 2160 pixels. 00:04:12

That's over 8 million pixels. 00:04:17

So think of the processing power that this TV has to have 00:04:19

to update an image that big, that many times every second. 00:04:23

The first thing you'll notice about a modern LCD screen 00:04:27

is that it's not only the active line of pixels 00:04:29

that retains brightness, it's the entire image. 00:04:31

So you can actually see the full image 00:04:34

as each scan line passes down the screen. 00:04:36

This is every frame of the startup sequence on an Xbox One. 00:04:38

I also recorded myself playing a game of Halo. 00:04:51

Nothing will make you feel worse about your performance 00:04:53

than watching your lousy aim in slow-mo. 00:04:55

Look at that. 00:04:57

It's crazy to think that when you're playing Halo, 00:04:58

this is actually what is happening on your TV. 00:05:00

If only you could see at this speed, 00:05:03

your aim would be incredible. 00:05:04

It honestly makes me feel bad 00:05:06

when I fall asleep watching TV, 00:05:08

knowing that this TV is doing all this intensive work, 00:05:10

changing literally tens of millions of pixels every second, 00:05:12

and there's no one there watching it. 00:05:17

Here's a fun fact, the same applies to an iPhone, 00:05:19

except it's in portrait mode. 00:05:21

So if you're watching a video in landscape mode 00:05:24

on your iPhone, you're actually getting updates 00:05:27

from left to right, or right to left, 00:05:29

depending on which way you flipped it. 00:05:30

And that just proved to me that you can't see 00:05:33

the refresh direction with your naked eye. 00:05:34

Because I had no idea, 00:05:36

whenever I was watching a YouTube video on my iPhone, 00:05:37

that the screen was updating 00:05:39

in a completely different direction. 00:05:40

I'm not sure if this is the case for all smartphones, 00:05:42

but it's certainly the case on an iPhone 7 Plus, 00:05:44

which is what I filmed this on. 00:05:46

So we've talked about one illusion of TVs, 00:05:48

the illusion of movement. 00:05:49

The second illusion I wanna talk about 00:05:51

is the illusion of color. 00:05:53

For this next part, I'm gonna need a second camera. 00:05:54

Here's one. 00:05:57

That's you, I love you. 00:05:58

So, in order to film this screen extremely close, 00:06:00

I have to set my focus at the minimum possible distance. 00:06:03

So it's sort of like right here now. 00:06:06

Set to my minimum focus. 00:06:08

As I slowly move towards the screen, it becomes sharper. 00:06:09

And you will then at the last minute 00:06:12

see a very odd looking pattern. 00:06:14

And what you're seeing there 00:06:18

is an effect caused by the camera, this camera, 00:06:19

trying to resolve individual pixels 00:06:22

on the surface of this screen. 00:06:25

As I push further forward, the effect disappears 00:06:27

and everything goes out of focus. 00:06:31

That's because I'm now beyond 00:06:32

the minimum focal distance of this lens, 00:06:34

which is about, well, it's about there. 00:06:36

Not close enough. 00:06:40

In order to get closer, I'm gonna need a macro lens. 00:06:41

Here's one. 00:06:46

As I approach the white 00:06:47

and everything starts to become in focus, 00:06:49

you can see that white isn't so white anymore. 00:06:54

It looks like I have to go closer even than that. 00:06:56

Thankfully, I can go all the way 00:07:00

to five times magnification. 00:07:02

Now, one thing from this point, 00:07:05

I am definitely gonna need a tripod 00:07:06

because there's no way my arms are sturdy enough 00:07:08

to hold this in place, but I'll just ease it in 00:07:10

just to show you the level of magnification 00:07:13

we're talking about now. 00:07:15

Well, it's close, it's a different story altogether. 00:07:21

I'm gonna get a tripod. 00:07:24

Here's one. 00:07:25

What a mission this is. 00:07:28

All right, let's see what we can do here. 00:07:29

We're so close up right now 00:07:31

that I can actually disturb this image 00:07:33

by blowing on the lens. 00:07:35

We're now looking at the sub-pixel level. 00:07:39

A pixel is made up of three sub-pixels, 00:07:41

red, green, and blue, RGB. 00:07:44

You may have heard that before. 00:07:46

And this creates the illusion of different colors. 00:07:48

By dimming and brightening different sub-pixels 00:07:51

to different intensities, 00:07:54

this screen can create the illusion 00:07:56

of literally millions of different colors. 00:07:58

When all three are lit to full brightness, you get white. 00:08:01

When all three dim, 00:08:04

you go through gray all the way down to black. 00:08:05

So if green dims away and red and blue are still lit, 00:08:07

then you go into magenta, purple, that sort of area. 00:08:10

And that's how the colors are made. 00:08:13

So every time on your TV, you're looking at a white image, 00:08:14

you're looking at tons of blue, green, and red lights. 00:08:18

They're just so small, they look like white to your eye. 00:08:23

Before you get white, red, green, and blue 00:08:27

blurs into yellow, cyan, and magenta. 00:08:30

And that's what happens here 00:08:32

when I move the screen slightly out of focus. 00:08:33

This is too close to watch a Slow Mo Guys video. 00:08:38

I might vomit. 00:08:41

It's the same situation, just entire blocks, 00:08:44

and they're bigger. 00:08:48

As I mentioned before, this is a 4K LCD screen, 00:08:50

which a while back were typically lit by CCFLs, 00:08:53

or a cold cathode fluorescent lamp, 00:08:57

which means the entire panel is backlit by fluorescent tubes. 00:09:00

Nowadays, they are backlit by LEDs. 00:09:05

This is why this would actually be marketed as an LED TV. 00:09:08

The benefit of LED screens over CCFL screens 00:09:12

is that they're a lot thinner. 00:09:15

Now I'm gonna point it at where some black text is. 00:09:17

Now interestingly, even though this area is black, 00:09:20

because all the sub pixels have dimmed, 00:09:23

they are still in fact backlit. 00:09:26

Let me show you that right now. 00:09:28

Now you can see as we push in here, 00:09:30

you have to pardon the noise, 00:09:31

an extremely high iso to get this shot through a macro lens you can see even the dimmed pixels 00:09:32

part of the liquid crystal display is it's now trying to block all light from penetrating through 00:09:38

but it's still a backlit pixel and that's one of the fundamental limitations of an lcd screen 00:09:42

you can see this effect on an lcd screen in the credits of a film because you've got almost 00:09:48

completely black image but because there's white text the entire backlight has to be on to display 00:09:52

the white which means light will leak out from the black pixels which means it's not true black 00:09:57

There is another technology that's becoming much more common these days, and that is an OLED screen, organic light-emitting diode. 00:10:02

I did want to include a comparison between an LCD panel and an OLED panel, but I didn't actually have an OLED TV. 00:10:09

And by sheer luck, right in the middle of me shooting all this footage, LG got in touch and offered to supply me with an OLED TV for the purpose of making this video, which I really appreciate. 00:10:15

Thanks, LG. 00:10:25

Why don't we go and take a look at it? 00:10:26

This is a 77-inch LG OLED TV. 00:10:27

The way OLED technology works is that each pixel is self-illuminating, 00:10:31

depending on how much voltage is passing through it, 00:10:36

which means there's no global backlight on the TV. 00:10:38

Each pixel is individually in control of how bright it is, 00:10:41

and it's not being lit from behind. 00:10:45

And that means when we go to our high ISO experiment, just like we did on the LCD, 00:10:46

that when there's an area of black on the screen, all of those pixels are off. 00:10:52

And you can see here where I'm putting my cursor in front of the lens, 00:10:57

You can see each subpixel lighting up and then completely turning off when it goes away. 00:11:00

This technology means much deeper blacks and the possibility of a very thin screen. 00:11:05

And there you have it, a brief explanation of how a TV works in slow-mo. 00:11:11

If you found that video interesting, chances are you might find some other 00:11:15

videos interesting on this channel, so make sure you boop! 00:11:19

And once you've booped, feel free to check out our... 00:11:22

It's just there. 00:11:27

thank you very much for watching that was good timing wasn't it tv timed out and all this fireworks 00:11:27

Subido por:: Antonio S.
Licencia:: Reconocimiento - No comercial - Compartir igual
Visualizaciones:: 9
Fecha:: 10 de diciembre de 2018 - 18:11
Visibilidad:: Público
Centro:: IES ANTONIO MACHADO
Duración:: 11′ 38″
Relación de aspecto:: 1.78:1
Resolución:: 1280x720 píxeles
Tamaño:: 64.98 MBytes

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