Rolling Shutter and Sensor Readout Speed Explained

What is rolling shutter

Most digital cameras do not expose the entire sensor at one instant. Instead, the sensor reads out the image line by line, from top to bottom, over a short but nonzero period. This is called a rolling shutter. The time it takes to read the whole sensor is the readout speed, and it directly determines how much distortion you see in moving frames.

When the subject moves or the camera pans during that readout, each row captures a slightly different moment. Vertical objects lean to one side, rotating objects shear, and handheld pans gain a jello-like wobble. The effect is most visible in video because you see the result as a continuous motion instead of a single freeze frame.

The alternative is a global shutter, where all pixels are exposed at the same instant and then transferred to storage. Global shutter sensors are common in professional cinema cameras and are becoming more available in consumer models, but most interchangeable-lens and compact cameras still use a rolling shutter because it allows faster continuous shooting and higher resolution for a given cost.

A mechanical shutter also avoids the problem for stills: the front curtain moves out of the way, and the rear curtain closes after the exposure, so all rows receive light at effectively the same time. For video, though, the choice is between rolling and global electronic shutters. If you mainly shoot video, readout speed matters much more than the shutter type.

Related reading: shutter types explained and frame rate basics.

• Rolling shutter: rows read sequentially, top to bottom
• Readout speed: time to scan the full sensor
• Global shutter: all rows exposed simultaneously

Why vertical lines lean, wobble, and band

The classic rolling shutter symptom is a vertical line that appears to lean. Imagine a doorframe filling the frame. If the camera pans left while the sensor reads top to bottom, the top of the frame was captured earlier and the bottom later, so the doorframe appears to tilt. The faster the pan and the slower the readout, the more extreme the lean.

The same mechanism causes wobble in handheld footage. A slight shake makes rows shift relative to each other, producing a wavy, gelatin-like motion. It is most noticeable with long telephoto lenses and when you are walking or running with the camera.

Banding under artificial light is a related but different artifact. LED and fluorescent lights flicker at twice the mains frequency, usually 100 or 120 Hz. With a rolling shutter, different rows are exposed under different parts of the flicker cycle, so you see alternating bright and dark bands that move up and down. A slower readout makes the banding wider and more obvious.

A few shooting choices reduce the effect: use a mechanical shutter for stills, choose a shutter speed close to the flicker frequency, or use a camera with a fast readout. You can also accept a slight skew when the subject is static and the camera is on a tripod, since nothing changes between rows.

For a more detailed look at exposure timing, see shutter speed explained.

What to check in the specs

Camera makers rarely list readout speed in milliseconds, so you need indirect clues. The most useful figure is the sensor scan time for video, which is often listed as a number like 8.4 ms (typical for a stacked CMOS sensor) or 25 ms (typical for a slower readout). When a spec sheet gives a scan time, lower is better.

If the spec sheet does not state scan time, look for the sensor architecture. Stacked CMOS sensors separate the photodiodes from the readout circuitry, allowing much faster transfer. Sony and Canon both produce stacked sensors for high-end models, and Nikon uses them in some Z series cameras. The term "stacked" is a strong hint that readout is fast.

The maximum video resolution and frame rate also give a clue. A camera that records 4K at 60p or 120p must read the sensor quickly, so the same sensor will have less rolling shutter at 24p and 30p. Conversely, a camera that only manages 4K at 30p is likely to show more skew. Check the 4K video guide for typical specs.

Another hint is the fastest electronic shutter speed. Cameras with very fast electronic shutter speeds, such as 1/32000 s, tend to have quick readouts, because the exposure is so short that the scan must be fast enough to avoid visible banding. This is not guaranteed, but it correlates.

Finally, look at the sensor size and resolution. All else being equal, a smaller sensor or a lower resolution readout is faster because there are fewer rows to clock. A 1-inch sensor camera with 20 megapixels will generally read out faster than a full-frame sensor with 45 megapixels, though newer stacked full-frame sensors beat larger sensors from a generation ago.

For cameras that you are comparing directly, the best approach is to search the spec sheet for "readout speed", "scan time", "sensor architecture", and "electronic shutter speed". If none of these appear, the manufacturer is not highlighting readout performance, which is often a sign that it is not a priority.

How to minimize the effect in your shots

You can avoid most rolling shutter artifacts without changing hardware. For still photography, use a mechanical shutter whenever possible. For video, the key is to reduce the speed of motion in the frame: pan slowly, use a wider lens, or move the camera on a gimbal instead of walking.

If you are shooting under LED or fluorescent lights, set the shutter speed to approximately double the local mains frequency. In 50 Hz regions, use 1/100 s; in 60 Hz regions, use 1/120 s. Many cameras have an anti-flicker or anti-banding setting that does this automatically. See white balance and light for more on artificial light.

Another workaround is to shoot at a lower resolution. Many cameras can record 1080p or 1080p60 by reading out a smaller portion of the sensor, which cuts the number of rows and shortens the scan time. The trade-off is lower detail, but for web and social use it is often invisible.

For stills, you can also use the electronic shutter when the subject is completely static and the camera is locked down. The skew is zero because nothing moves during the scan. The risk only appears with motion in the frame.

The most reliable fix is to choose a camera with a global shutter or a very fast readout. See the best video cameras and best 4K cameras for models that prioritize this.

Does sensor size make rolling shutter worse

Larger sensors do not inherently have worse rolling shutter; the issue is pixel count and readout circuitry. A full-frame sensor with 45 megapixels needs to move more data than a 1-inch sensor with 20 megapixels, but a stacked full-frame sensor can still be faster than a non-stacked smaller sensor.

For action cameras and compact cameras, sensor size is small, so readout is generally fast. Many action cameras now offer 4K at 60p or 120p, which indicates a quick scan. If your priority is minimizing skew in video, a compact or action camera is often a safer bet than a large-sensor camera with a slow readout.

The trade-off is dynamic range and low-light performance, where the smaller sensor is at a disadvantage. See sensor size explained and crop factor for the full picture.

If you need both large-sensor image quality and low rolling shutter, look for a stacked full-frame camera. The premium is real, but the performance is in a different class.

What to pick for your use

Questions

How do I know the readout speed of a camera?

Check the spec sheet for a value in milliseconds. If it is not listed, look for a stacked sensor, a high 4K frame rate, or a very fast electronic shutter speed as indirect signs.

Is rolling shutter always visible?

No. It only appears when there is motion in the frame or when the camera moves during the readout. Static scenes and locked-off tripod shots are unaffected.

Does a mechanical shutter eliminate rolling shutter?

Yes, for stills. A mechanical shutter exposes the whole sensor at nearly the same time. For video, the sensor readout still happens row by row, so the effect remains.

What is the difference between rolling and global shutter?

A rolling shutter reads the sensor line by line. A global shutter exposes all rows at once. Global shutter sensors are faster but more expensive and less common in consumer cameras.

Can I fix rolling shutter in post?

Some video editors have a rolling shutter correction tool that estimates and removes skew. It works well for mild cases, but not for severe wobble or banding.