Why Do Cameras Do This? | Rolling Shutter Explained - Smarter Every Day 172
What's up? I'm Destin. This is Smarter Every Day. Get your phone out. You see that little camera assembly there? Let's take it out of the phone. Yep. That's what it looks like.
So here's what we're going to do. The first thing we're going to do is pop the lens off, and there we go. That is called a CMOS sensor. That is the camera on your phone. Complimentary Metal-Oxide Semiconductor. So, when you take a photo or a video with your phone, you would think that it exposed that entire chip at one time, like snapping a photo. That's not how it works. It actually scans down the chip, and that's how images are created.
This is called "rolling shutter," and it's the exact reason your cell phone makes weird shapes out of fast-moving objects. This is a flatbed scanner, and I have a circular patch right here. If I were to take this patch and set it face down on the scanner, and I were to start the scanner and move the patch in the same direction as that moving row of pixels, check out what happens. You're smart-- is this going to look like a circle? No! It's not a circle. It's stretched out. And that makes sense, right? You're stretching that image because you're moving it along with the scanner.
Now, conversely, what's going to happen if instead of moving it with the scanning row pixels, we move opposite? It's not going to stretch it out, is it? What's it going to do? It's going to compress that circle down. A rolling shutter on your cell phone camera is very much like this, except it goes from the top of the image all the way down to the bottom. That means that what you're seeing is actually a lie. It's like a stack up of several different moments.
Okay, now that we understand how this works, it's time to visualize it in the most turbo-awesome way possible. Over the past three years, anytime I had a phone and a high-speed camera at the same place at the same time, I would be on the lookout for rolling shutter events. And I would video it with the phone and then I would video it with a high-speed camera, so that I could go back and manually simulate rolling shutter so that I could understand exactly how the artifacts were created.
This is so stinking cool! Your brain's going to get it, instantly! We'll start with iPhone video and then we'll go to the simulation.
This is what your camera does dozens of times per second. I noticed that the patterns looked very different depending on which way the propeller was rotating relative to the rolling shutter. This is really beautiful, but I was kind of bummed that I didn't get to see the effect head-on to the propeller. A couple of years later, though, when I was taking high altitude flight lessons near Pike's Peak in Colorado, I finally got my chance to video a propeller head-on on the Tarmac.
The fidget spinner community has known for a while now that when it's really bright outside, a cell phone camera videoing a fidget spinner will turn it into what they call "the thing." It's just rolling shutter with a little bit of aliasing thrown in, but it looks like some kind of Ninja Alien throwing star. Anyway, when you slow it down with a high-speed camera, you can really reveal the map that makes this look so weird.
My buddy Ben plays both the Mandolin and the guitar, and it took us a really long time to get the rolling shutter effect to show itself. But when we did, it was awesome! Guitar strings are especially difficult because they vibrate so quickly that a normal high-speed camera isn't fast enough. We had to record them at 20,000 or 28,000 frames per second to be able to run this simulation properly.
The last trick is something I had never seen before, but somebody told me about it. If you video a coin spinning, you can see a swirl pattern on the edge of the coin. Yep, that's also rolling shutter. Obviously this took a really long time to make, and Henry from MinutePhysics made it possible. He's the guy that figured out exactly how to make after effects simulate rolling shutter.
On the behind the scenes video, on the second channel, Henry and I talked about what we were trying to accomplish. Go check it out. And we'll, uh, we'll throw some love Henry's way. Also, I want to say thanks to the sponsor, which is Audible. Before we talk about the book that I'm listening to on Audible right now, let's go goof around with rolling shutter and some chickens.
Okay, the book I'm currently listening to on Audible is called "The Devil in the White City." It's a really good book about the 1893 Chicago World's Fair. A fair that I had no idea changed America, but it did. Also, America's first serial killer, so there's that. It's pretty crazy. I had no idea. It's a great story. You should check it out. "Devil in the White City," by Erik Larson. You will enjoy it.
You can get that by going to audible.com/smarter. That is two things: number one, you get a free audiobook; number two, I get secret internet points because Audible knows you came from SmarterEveryDay. And they're more likely to support Smarter Every Day in the future, and that's a big deal for me and the family. I appreciate that.
Anyway, if you see anybody that talks about rolling shutter, make sure they don't get confused with aliasing. That's the wagon wheel effect. A lot of people get those two confused. I hope this video earned your subscription. If it didn't, no big deal. I'm Destin, you're getting Smarter Every Day. Have a good one! Bye. Last chicken. Brave chicken.