Rolling Shutter vs. Global Shutter: The Camera Problem You Didn't Know About
Why Your Super-Fast Memory Card Isn't Enough
When people want to take pictures of fast action, they buy the fastest memory cards they can find. They think speed is all about how fast the camera can save the photo.
But what if the problem isn't how fast you save the picture, but how the camera takes the picture in the first place? There's a hidden part of your camera's sensor, called a shutter, that can cause big problems for fast-moving things, no matter how speedy your memory card is.
This guide will explain the difference between two types of shutters: the Rolling Shutter and the Global Shutter. You'll learn why one causes problems and why the other is the future of photography.
How a Digital Camera Takes a Picture
First, let's be clear: we're not talking about the clicking sound you hear in a big camera. That's a physical curtain. We're talking about the electronic shutter on the sensor itself. The sensor is the computer chip covered in tiny dots (pixels) that see the light. The important difference is in how these pixels read the light to make a picture.
1. The Rolling Shutter: Like a Scanner
Most cameras today, including the one in your phone, use a Rolling Shutter.
Imagine your camera's sensor is like a scanner in an office. It doesn't see the whole page at once. It scans it line by line from top to bottom. A rolling shutter does the same thing with light.
It starts at the top: The first row of pixels starts soaking up light.
It "rolls" down: A split second later, the second row starts. Then the third, and so on, until the last row at the bottom finally starts.
It finishes at the top: By the time the bottom row starts recording, the top row has already finished and sent its information to the camera's brain.
Because of this top-to-bottom "rolling" process, the camera never captures the whole scene at the exact same instant.It's actually a picture stitched together from many slightly different moments in time.
2. The Global Shutter: A True Snapshot
The Global Shutter is the perfect way to take a picture. It's what professional movie cameras and high-tech robots use.
Instead of scanning line by line, a global shutter acts like a flash of light.
Ready, Set, Go!: All the pixels on the sensor start recording light at the exact same moment.
And... Stop!: They all stop recording at the exact same moment, too.
Perfect Picture: The entire image is captured in a single, perfect instant. Each pixel has its own tiny bit of memory to hold onto its information until the camera is ready to save it.
A Global Shutter gives you a true snapshot, freezing a moment perfectly in time.
Problems Caused by the Rolling Shutter
Because the rolling shutter captures the picture line by line, it creates weird effects when things are moving fast.
1. The "Jello" Effect
This is the biggest and most obvious problem. Fast-moving objects get distorted and look bent or wobbly.
Spinning Propellers: A helicopter's blades might look like they are made of bent rubber. That's because the top of the sensor saw the blade in one position, but by the time the bottom of the sensor saw it, the blade had already moved.
Leaning Buildings: If you're in a car and take a picture of a building as you drive by, the building might look like it's leaning.
Wobbly Videos: Shaky hands can make your videos look like they are made of Jello, because every frame is being slightly distorted by the movement.
2. Problems with Flash
A rolling shutter also makes it hard to use a flash. A flash is a very quick burst of light.
The Black Bar: Because the sensor is scanning from top to bottom, the super-short flash might only happen when the sensor is halfway through its scan. The result? The top half of your photo is dark, and only the bottom half is lit up by the flash.
The Workaround: To get around this, cameras have a special mode (called High-Speed Sync or HSS) that makes the flash pulse like a strobe light instead of one big flash. It works, but it also makes the flash much weaker.
3. Flickering Lights in Videos
If you've ever recorded a video indoors, you might have seen dark bands rolling through your video. This is caused by the rolling shutter fighting with the flicker of indoor lights (which actually turn on and off very quickly, even if you can't see it). Some rows of the sensor see the light when it's bright, and others see it when it's dim, creating ugly bands.
The Global Shutter Solves Everything
A Global Shutter fixes all of these problems because it captures everything at once.
How Do They Work?
In the past, global shutters had a problem. To add that tiny piece of memory to each pixel, you had to take away some of its light-gathering area. This made pictures darker and noisier.
But now, engineers have figured out two clever tricks:
BSI (Back-Illuminated Sensor): They moved all the wiring to the back of the sensor, so more light can hit the front.
Stacked Sensor: They build the sensor like a skyscraper, putting the memory "floor" underneath the light-catching "floor." This way, the memory doesn't block any light.
These tricks mean that new global shutters can take pictures that are just as bright and clean as any other camera.
What It Means for Photographers
Perfect Flash, Every Time: You can use your flash at any shutter speed, as fast as you want, and it will always light up the whole picture perfectly.
No More "Jello": All those weird, wobbly, and bent distortions are completely gone. Fast-moving cars, spinning propellers, and quick pans in videos will all look perfectly sharp and normal.
How This Affects Your Memory Card
A global shutter changes the way a camera sends information to the memory card.
A rolling shutter sends data like a steady stream from a garden hose.
A global shutter dumps all the data at once, like kicking over a huge bucket of water.
To handle that sudden flood of information, you need a very fast memory card, like a V90 SD card or the even faster CFexpress cards. The camera's computer also doesn't have to waste time trying to fix "jello" effects, so it can focus on sending the perfect picture to your card as quickly as possible.
A New Standard for Cameras
Worrying about memory card speed is about how fast you can save a picture. Worrying about the shutter is about how well you take the picture in the first place.
For a long time, we just had to live with the problems of the rolling shutter. But now, global shutter technology is here and ready for everyone.
For Photographers: It means no more limits on your flash and no more weird-looking action shots.
For Videographers: It means no more wobbly videos or flickering bands from lights.
For Your Camera: It means the whole system—from the sensor to the processor to the memory card—is built for perfect, high-speed performance.
The time of bent propellers and wobbly videos is ending. The global shutter is here, and it’s changing photography for the better.
