How a TV Works in Slow Motion - The Slow Mo Guys
Hello there, my name’s Gavin, and welcome to this episode of The Slow Mo Guys very oddly presented from my living room.
A while ago, I made a video called “How a Camera Works In Slow Mo”, and the response was great. So I thought a good natural progression to that video would be how a TV works in slow mo.
This is an 85-inch LCD TV, and whenever I’m playing something on it or watching something on it, my eyes and brain are being misled and tricked, giving me the illusion of watching a moving object when in fact I’m just watching several still images just shown to me very, very fast. If I’m watching a film, I’m being shown 24 images every second, and to my eyes, that looks like I’m looking at a moving object when in fact I’m looking at 24 individual pictures. If I’m playing a game, it’s the same, except maybe 30 to 60 frames a second, and if I’m on a PC, it could be 100s, PC master race.
But a TV like this is actually incapable of showing you one image and then 1/24 of a second later just switching all at once to the next image, and to illustrate this next point, I’m gonna use a very old and very crap CRT TV. That stands for cathode ray tube. If you’ve ever seen one of these filmed, you may notice that it looks slightly different on camera than it does to your eye. Look at that.
The reason it looks like this is because the shutter speed of this camera is out of sync with the refresh rate of this screen. The frame is constructed from the top to the bottom multiple times per second; that’s 60 times in the US, 60 Hertz. I’ve prepared for you some high speed footage that I shot a long time ago on the v2511 of this screen and this screen and some others. A lot of it is Dan paying “Super Mario” on the NES extremely badly.
Here’s the TV and the cat played back at 25; this is how it would be perceived in real time. And now at 1600 frames a second, you can actually see the scan line moving from the top to the bottom, and you’ll notice that on a CRT screen, it’s only the active line of pixels that’s bright, and your persistence of vision will actually build that into a complete image. It’s messing with my eyes, this. - It’s like a dance floor. Oh, I didn’t even make it past the first guy. -
Slowed all the way down to 2500 frames a second, you can now differentiate each individual frame being built from top to bottom. It takes an extremely fast camera to see that each frame is built line by line from top to bottom, but it takes an even faster camera to see that each line is drawn from left to right. Slowed down to 28,500 frames a second, we’re now seeing glimpses of that, but we do need to go even slower. This is now 118,000 frames a second, and I’m gonna put the stats up for you here so you can see the actual amount of time that it took, and you can see now that the line is being drawn from left to right on the screen.
Now at 146,000 frames a second, to gain perspective on just how slow this actually is, you can see the exact time I shot this. So this is hours, it was just past midnight, 23 minutes, 41 seconds, this is 1/10 of a second, 1/100 of a second, 1/1000 of a second or a millisecond, and then over here you’ve got 1/10,000 of a second, 1/100,000 of a second, and this unit here is the millionth of a second, or a microsecond.
We are now at 380,000 frames a second as our recording frame rate. That is the highest frame rate we’ve ever shot so far on this channel, and using this information, here’s a little bonus fact: a CRT screen can draw Mario’s mustache in less than 1/380,000 of a second. That is some seriously fast facial hair.
And if you’re wondering why this footage looks extremely mucky and blurry, it’s because the resolution is only 256 by 128, which, plonked into a 4K frame, is this big. That CRT screen is standard def; this is a 4K screen, which means it’s 3840 by 2160 pixels. That’s over eight million pixels. So think of the processing power that this TV has to have to update an image that big that many times every second.
The first thing you’ll notice about a modern LCD screen is that it’s not only the active line of pixels that retains brightness; it’s the entire image. So you can actually see the full image as each scan-line passes down the screen. This is every frame of the start-up sequence on an Xbox One. I also recorded myself playing a game of “Halo”. Nothing will make you feel worse about your performance than watching your lousy aim in slow mo, look at that. It’s crazy to think that when you’re playing “Halo”, this is actually what is happening on your TV. If only you could see at this speed, your aim would be incredible.
It honestly makes me feel bad when I fall asleep watching TV, knowing that this TV is doing all this intensive work changing literally 10s of millions of pixels every second, and there’s no one there watching it. Here’s a fun fact: the same applies to an iPhone, except it’s in portrait mode. So if you’re watching a video in landscape mode on your iPhone, you’re actually getting updates from left to right, or right to left, depending on which way you’ve flipped it, and that just proved to me that you can’t see the refresh direction with your naked eye, because I had no idea, whenever I was watching a YouTube video on my iPhone, that the screen was updating in a completely different direction. I’m not sure if this is the case for all smartphones, but it’s certainly the case on an iPhone 7 Plus, which is what I filmed this on.
So we’ve talked about one illusion of TVs, the illusion of movement. The second illusion I wanna talk about is the illusion of color. For this next part, I’m gonna need a second camera. Here’s one, that’s you, hello, you. So in order to film this screen extremely close, I’m gonna have to set my focus to the minimum possible distance, so it’s sort of like right here now.
Set to my minimum focus, as I slowly move towards the screen, it becomes sharper, and you will then, at the last minute, see a very odd looking pattern. And what you’re seeing there is an effect caused by the camera, this camera, trying to resolve individual pixels on the surface of this screen. As I push further forward, the effect disappears, and everything goes out of focus. That’s because I’m now beyond the minimum focal distance of this lens, which is about, well, that’s about there. Not close enough. In order to get closer, I’m gonna need a macro lens.
Here’s one. As I approach the white, and everything starts to become in focus, you can see that white isn’t so white anymore. It looks like I have to go closer even than that. Thankfully, I can go all the way to five times magnification. Now, one thing from this point, I am definitely gonna need a tripod, because there’s no way my arms are sturdy enough to hold this in place, but I’ll just ease it in just to show you the level of magnification we’re talking about now. Well, this close, it’s a different story altogether. I’m gonna get a tripod. Here’s one.
What a mission this is, all right, let’s see what we can do here. We’re so close up right now that I can actually disturb this image by blowing on the lens. We’re now looking at the sub-pixel level. A pixel is made up of three sub-pixels, red, green, and blue, RGB, you may have heard that before, and this creates the illusion of different colors. By dimming and brightening different sub-pixels to different intensities, this screen can create the illusion of literally millions of different colors. When all three are lit to full brightness, you get white. When all three dim, you go through gray all the way down to black. So if green dims away, and red and blue are still lit, then you go into magenta, purple, that sort of area, and that’s how the colors are made. So every time on your TV you’re looking at a white image, you’re looking at tons of blue, green, and red lights. They’re just so small they look like white to your eye. Before you get white; red, green, and blue blurs into yellow, cyan, and magenta, and that’s what happens here when I move the screen slightly out of focus.
This is too close to watch a Slow Mo Guys video. I might vomit. It’s the same situation, just entire blocks and they’re bigger. As I mentioned before, this is a 4K LCD screen, which, a while back, were typically lit by CCFLs, or a cold cathode fluorescent lamp, which means the entire panel is backlit by fluorescent tubes. Nowadays, they are backlit by LEDs. This is why this would actually be marketed as an LED TV. The benefit of LED screens over CCFL screens is that they’re a lot thinner.
Now I’m gonna point it at where some black text is. Now, interestingly, even though this area is black because all the sub-pixels have dimmed, they are still in fact backlit. Let me show you that right now. Now you can see, as we push in here, you have to pardon the noise, we’re at an extremely high ISO to get this shot through a macro lens, but you can see even the dimmed pixels, part of the liquid crystal display as it’s now trying to block all light from penetrating through, but it’s still a backlit pixel, and that’s one of the fundamental limitations of an LCD screen.
You can see this effect on an LCD screen in the credits of a film, ‘cause you’ve got an almost completely black image, but because there’s white text, the entire backlight has to be on to display the white, which means light will leak out from the black pixels, which means it’s not true black. There is another technology that’s becoming much more common these days, and that is an OLED screen, organic light-emitting diode. I did wanna include a comparison between an LCD panel and an OLED panel, but I didn’t actually have an OLED TV, 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. Thanks, LG.
Why don’t we go and take a look at it. This is a 77-inch LG OLED TV. The way OLED technology works is that each pixel is self-illuminating, depending on how much voltage is passing through it, which means there’s no global backlight on the TV. Each pixel is individually in control of how bright it is, and it’s not being lit from behind. And that means, when we go to our high ISO experiment, just like we did on the LCD, that when there’s an area of black on the screen, all of those pixels are off, and you can see here where I’m putting my cursor in front of the lens, you can see each sub-pixel lighting up and then completely turning off when it goes away. This technology means much deeper blacks, and the possibility of a very thin screen. And there you have it: a brief explanation of how a TV works in slow mo. If you found that video interesting, chances are you might find some other videos interesting on this channel, so make sure you boop, and once you’ve booped, feel free to check out our it’s just there. Thank you very much for watching. That was good timing, weren’t it? TV timed out, and now there’s fireworks.