Rolling shutter is a method of capturing an image in which the sensor starts and ends exposure row by row instead of for all pixels at once, so the top and bottom of the frame are recorded at slightly different moments. In camera mechanics, the term describes both the readout behavior of most CMOS image sensors and the visual artifacts it produces when the camera or subject moves quickly.
Rolling shutter is not a defect in itself but a design trade-off. Reading rows sequentially keeps sensors simpler, less noisy and cheaper than a full global shutter, at the price of geometric distortion whenever motion during the readout time becomes visible.
How a rolling shutter reads the sensor
A rolling shutter works by resetting and reading each row of pixels in sequence. Every row receives the same exposure duration, but each one begins a little later than the row above it, so a narrow exposure window sweeps down the sensor like a scanning line.
The decisive parameter is the readout time, also called scan time or rolling shutter speed: the interval between the start of the first row and the start of the last row. It is independent of the chosen shutter speed. An exposure of 1/8000 s can still take 1/30 s to sweep the frame on a slow sensor, and any motion within that sweep is recorded as distortion.
Readout time depends on the number of rows, the analog-to-digital converter speed and the bit depth. The table summarizes typical ranges across sensor designs; actual values vary by model and mode.
| Sensor design | Typical readout time | Visible skew |
|---|---|---|
| Older conventional CMOS | 1/15 to 1/30 s | Strong with fast motion |
| Modern conventional CMOS | 1/40 to 1/60 s | Noticeable in pans and sports |
| Stacked CMOS | 1/120 to 1/250 s | Rarely noticeable |
| Fastest stacked sensors | Below 1/250 s | Close to global behavior |
Artifacts caused by rolling shutter
Rolling shutter artifacts appear when something changes faster than the readout sweep. Because each row samples a different moment, straight lines and steady light can be rendered as slanted, bent or banded shapes.
| Artifact | Typical trigger | Appearance |
|---|---|---|
| Skew | Fast horizontal pan or moving vehicle | Vertical lines lean to one side |
| Jello or wobble | Vibration or handheld shake in video | Frame appears to ripple |
| Partial exposure | Flash or lightning during readout | Only a band of the frame is lit |
| Banding under artificial light | Flickering LED or fluorescent lamps | Horizontal bright and dark stripes |
| Bent propellers | Rotating blades or wheels | Curved, detached blade shapes |
These effects are strongest with an electronic shutter, where the sensor readout alone defines the exposure. In video, rolling shutter is almost always present because video is recorded electronically, which is why handheld footage at long focal lengths often shows wobble.
Rolling shutter compared with other shutter types
Rolling shutter is best understood alongside the other shutter mechanisms in camera mechanics. A mechanical shutter also travels as a slit at fast speeds, but its curtains cross the frame in about 2 to 4 ms, far faster than most sensor readouts, so distortion is minimal.
| Shutter type | How exposure is timed | Motion distortion | Main drawback |
|---|---|---|---|
| Mechanical focal-plane shutter | Physical curtains travel across the sensor | Very low | Noise, wear, limited burst rate |
| Electronic first curtain | Electronic start, mechanical end | Very low | Possible bokeh clipping at high speeds |
| Electronic rolling shutter | Sequential row reset and readout | Low to strong, depends on readout | Skew, banding, flash limits |
| Global shutter | All pixels start and stop together | None | Higher cost, often more noise or lower dynamic range |
A global shutter removes the problem entirely by storing every pixel at the same moment, but it requires extra circuitry per pixel. This has historically meant lower dynamic range or higher noise, which is why rolling designs still dominate in general photography.
Managing rolling shutter in practice
Photographers manage rolling shutter by choosing the right shutter mode for the subject and by knowing their camera’s readout limits. Silent electronic shooting is ideal for static subjects and quiet venues, while fast action usually benefits from the mechanical shutter on cameras with slower sensors.
| Situation | Recommended choice | Reason |
|---|---|---|
| Sports with slow-readout camera | Mechanical shutter | Curtains are faster than the readout |
| Silent event or wildlife | Electronic shutter, steady framing | Avoid fast pans to limit skew |
| Flicker from LED lighting | Mechanical shutter or flicker reduction | Reduces banding from pulsed light |
| Handheld video at long focal length | Stabilization and lower crop modes | Reduces wobble and readout time |
| Flash photography | Mechanical or electronic first curtain | Electronic readout limits flash sync |
In video, lower resolutions or crop modes often shorten readout because fewer rows are read. Software correction in editing applications can reduce skew and wobble, but it cannot fully restore geometry that was never captured correctly.
Common misconceptions about rolling shutter
- A faster shutter speed does not cure skew. It reduces motion blur within each row, but the readout time between rows stays the same.
- Mechanical shutters are not completely free of the effect. Their slit also travels, but so fast that distortion is usually invisible.
- IBIS does not remove rolling shutter. In-body stabilization reduces shake, which reduces wobble, but cannot change readout speed.
- Stacked sensors are not global shutters. They read much faster, yet still read rows sequentially.
In simple terms
Most digital cameras do not take a picture all at once. They scan the image from top to bottom, a bit like a photocopier, only very fast. If nothing moves during that short scan, the picture looks perfect.
If the camera or the subject moves quickly, the top of the picture is taken at a slightly different moment than the bottom. That is why straight poles can look tilted and propellers can look bent. Faster sensors make the scan so short that the effect almost disappears.
A practical example
A photographer covers a motor race with a mirrorless camera that has a conventional sensor and a readout time of about 1/40 s. Using the silent electronic shutter at 1/2000 s while panning with the cars, she notices that the wheels look oval and the fences lean in every frame.
She switches to the mechanical shutter, whose curtains cross the frame in a few milliseconds, and keeps the same 1/2000 s exposure. The leaning fences disappear and the wheels are round again, at the cost of a slightly lower burst rate.
The result shows the key lesson of rolling shutter: readout time, not shutter speed, decides geometric distortion. On a later assignment with a stacked-sensor body, she can use the electronic shutter without visible skew.