Rolling Shutter: Why Moving Subjects Bend and How to Prevent It

Rolling shutter is the distortion you get because a camera sensor is read one row at a time, not all at once. Reading the whole frame takes anywhere from a few thousandths of a second to roughly 1/10 second, so one edge of the picture is recorded later than the other. Anything that moves during that gap leans, bends or wobbles, and flickering lights turn into horizontal bands.

The menu choice between shutter modes is compared in mechanical vs electronic shutter, and the setting is defined in electronic shutter. This guide goes further into the artifact itself: the arithmetic that predicts how far a subject will lean, why a faster shutter speed does not cure it, how each symptom arises, what to do about each one, and how to measure your own camera’s readout time with a light bulb.

How a sensor reads a frame one row at a time

Almost every current camera and phone uses a CMOS sensor. In the usual design the pixels cannot all be measured at the same instant. The camera works through the sensor row by row: it clears a row, lets it collect light for the exposure time, reads it, and moves to the next. Every row gets the same length of exposure. What differs is when that exposure happens.

Picture a narrow horizontal strip sliding from one edge of the sensor to the other. Only the rows inside the strip are collecting light. The height of the strip is set by the shutter speed: a short exposure gives a thin strip, a long one a tall strip. The speed at which the strip travels is fixed by the sensor’s electronics and does not change with shutter speed.

Readout time is how long the camera takes to get from the first row to the last, and it decides how strong every rolling shutter effect is. Conventional sensors in electronic shutter mode commonly take somewhere between 1/10 and 1/60 second at full resolution, which is slow compared with most action. The figure often changes with the mode: a crop mode reads fewer rows and usually finishes sooner, and video modes that skip or combine rows read faster than modes that sample every row.

A mechanical shutter is a moving slit too

A focal plane shutter has two curtains. The first opens to start the exposure and the second follows to end it. At slow speeds the first curtain finishes its trip before the second one starts, so for a moment the whole sensor is uncovered. At fast speeds the second curtain sets off before the first has arrived, and the exposure is made by a slit travelling across the sensor.

That is the same geometry as electronic readout: a strip that sweeps the frame, with every row exposed for the same time at a slightly different moment. A mechanical shutter therefore produces rolling shutter distortion as well. The famous early racing photograph by Jacques Henri Lartigue, with its oval, leaning wheel and spectators leaning the other way, was made by a slow slit shutter combined with a pan.

The difference today is speed. Modern curtains cross the sensor in a few thousandths of a second, in the region of 1/250 to 1/400 second on many cameras. That is many times quicker than the electronic readout of a conventional sensor, so the same subject leans by a correspondingly smaller amount, usually too little to notice.

Electronic first curtain modes behave like the mechanical case. Each row’s exposure is started electronically in step with the curtain, and the mechanical second curtain ends it, so the sweep still takes one curtain travel time.

Which shutter mode should you leave the camera in day to day? Mechanical vs electronic shutter covers the three shutter modes in your menu, curtain travel time and readout time.

Skew: leaning verticals and bent subjects

Skew appears when something moves sideways at a steady rate while the sweep passes over it. Each row records the subject a little further along than the row before, so a vertical edge is drawn as a slant.

Working out how far a subject will lean

You need two times: how long the subject takes to cross the frame, and the readout time.

1. A car crosses the width of the frame in 1/2 second.
2. The readout time is 1/20 second.
3. During one full sweep the car travels 1/20 divided by 1/2, which is one tenth of the frame width.
4. The car fills a quarter of the frame height, so the sweep passes over it in a quarter of the time. Its roof and its wheels are offset by 2.5 percent of the frame width.

On an image 6000 pixels wide that is 150 pixels of lean, which is obvious. Run the same sum with a mechanical shutter that crosses the sensor in 1/300 second and the offset drops to about 10 pixels.

Two things follow from that arithmetic:

• Shutter speed is not in the sum. A faster exposure makes each row sharper. It does not bring the rows closer together in time. A frame at 1/8000 second in electronic shutter mode shows a crisp, clearly slanted car.
• What matters is speed across the frame, not speed over the ground. A distant jet drifts slowly through the picture and barely leans. A cyclist passing two meters away crosses it in an instant. A long lens magnifies movement, so a pan at telephoto lengths skews more than the same pan with a wide lens.

Which way the lean goes depends on which end of the frame the camera records first, and that differs between cameras and shutter modes. The rule is always the same: the part recorded later is shifted further in the direction of the movement.

Pans, rotation and motion along the sweep

A moving camera does the same thing to a still scene. Swing the camera quickly past a building and its walls slant. In panning you follow the subject, so the subject holds still in the frame and stays upright while the background takes the lean, where blur usually hides it.

Rotation gives stranger results because every part of the subject moves in a different direction. A propeller turning 40 times per second completes a full turn during a 1/40 second readout, so each row catches the blades at a different angle. Blades come out curved, uneven in number, or detached from the hub. Golf clubs, bats and the wings of small birds bend for the same reason.

Movement along the sweep changes length instead of angle. A subject travelling in the same direction as the sweep is stretched; one travelling against it is squashed. Turning the camera to portrait orientation therefore changes the look of the distortion without removing it.

What to do about skew

• Use the mechanical shutter or electronic first curtain for action stills unless the sensor has a fast readout.
• Keep silent electronic shutter for subjects that hold still: landscapes, architecture, quiet ceremonies.
• If you must shoot silently, try a crop mode, and step back or go wider so the subject crosses the frame more slowly.
• In video, slow the pan. If a vertical edge takes several seconds to cross the frame, the lean is too small to see.

Photographing aircraft with spinning blades? Air show and aircraft photography covers shutter speed by aircraft type (freeze jets, blur propellers and rotors) and panning a long lens across the sky.

Wobble: why video turns to jelly

Skew comes from steady movement. Wobble comes from vibration. If the camera shakes back and forth faster than the sensor can finish a sweep, the top of the frame is recorded while the camera is displaced one way and the bottom while it is displaced the other. Straight lines become S-shaped. Each frame catches a different phase of the shake, so on playback the picture ripples, an effect often called jello.

Typical sources are engine vibration through a vehicle mount, drone motors, footsteps, and a handheld telephoto.

• Stop the vibration reaching the camera. Use a damped mount, or hold the camera in your hands instead of bolting it to the vehicle. A gimbal removes large slow movements in walking shots.
• Use optical or sensor-shift image stabilization. It steadies the image before the rows are read, so there is less movement to record. It handles hand tremor well. It cannot keep up with fast engine buzz.
• Do not rely on software stabilization alone. Shifting and cropping whole frames after capture steadies the framing but leaves the bends inside each frame.
• Let motion blur hide what remains. A slower video shutter speed softens each row so the ripple is less crisp. In daylight that needs a neutral density filter.

Which shutter speed should video use? Camera settings for video covers frame rate, the 180-degree shutter rule and aperture for video.

Flash and flickering lights: bands instead of bends

The scene does not have to move for the sweep to show. If the light changes while the rows are being recorded, each row keeps whatever brightness it happened to receive.

Partial exposure with flash

A flash burst is over in about a thousandth of a second or less. It lights only the rows that are collecting light at that instant. With a mechanical shutter above the flash sync speed, that means the slit: the flash exposes one band and the rest of the frame stays dark.

Electronic readout obeys the same rule with a much slower sweep. The whole sensor is collecting light at once only when the exposure time is longer than the readout time, so the usable sync speed in fully electronic mode is roughly the readout time itself. On a conventional sensor that is very slow, which is why many cameras switch flash off in silent mode.

Other people’s flashes cause the same thing. At a wedding or press event, a guest’s flash that fires during your sweep leaves a bright stripe across your silent frame or your video. The stripe’s height is roughly the exposure time divided by the readout time: at 1/250 second with a 1/20 second readout it covers about 8 percent of the frame. Use the mechanical shutter at or below sync speed whenever flash is involved, yours or anyone else’s.

Need flash at a faster shutter speed than sync allows? High-speed sync covers how a focal-plane shutter turns into a travelling slit, why normal flash leaves a dark band, and how high-speed sync covers the whole sweep.

Banding under lights that flicker

Many mains-powered lights pulse at twice the mains frequency: 100 times per second on a 50 Hz supply and 120 times per second on a 60 Hz supply. If the exposure is shorter than one pulse, rows read during a bright moment come out lighter than rows read during a dim one. The result is soft horizontal bands.

The number of bands is the readout time multiplied by the flicker rate. A 1/20 second readout under 100 Hz flicker gives about five bands. A mechanical shutter with a 1/300 second sweep covers only a third of one pulse, so it shows a single gradient from top to bottom that changes from frame to frame.

• Match the pulse. Use 1/100 or 1/50 second on a 50 Hz supply, and 1/120 or 1/60 second on a 60 Hz supply. Each row then collects one or more complete pulses and the bands disappear.
• Expect trouble from dimmed LEDs and LED screens. Many are switched on and off hundreds or thousands of times per second, which gives many thin, hard-edged bands. Use a slower shutter speed, or the fine shutter speed adjustment some cameras offer, and change it in small steps until the bands vanish.

Which shutter speeds are safe under which lights? Flicker and banding under artificial light covers why lights flicker at twice the mains frequency, how flicker becomes bands and uneven frames, and flicker-safe shutter speeds.

Global shutter and stacked sensors

A global shutter starts and ends the exposure for every pixel at the same instant. Each pixel holds its charge in a small storage area until its turn to be read, so the slow part (the reading) happens after the picture has been captured. There is no sweep, so there is no skew, no wobble and no partial flash exposure, and flash can sync at any shutter speed.

The storage area takes room that would otherwise collect light. Global shutter sensors have tended to give up some image quality at low ISO compared with the best rolling designs, which is the main reason they remain a specialist choice. They also do not cure flicker: bands vanish, but whole frames come out lighter or darker depending on where in the pulse the exposure fell.

A stacked sensor is still a rolling design. Its readout circuitry sits in a layer behind the pixels, which lets the rows be read far faster, down to a few thousandths of a second. That brings electronic readout close to mechanical curtain speed, which is good enough for most action and makes silent bursts practical. The general background is in how image sensors work.

Common mistakes

• Raising the shutter speed to cure a leaning subject. The lean depends on readout time, not exposure time, so the slant stays and only gets sharper. Fix: switch to the mechanical shutter or a faster readout mode.
• Bolting an action camera or phone straight to a vehicle. Engine vibration travels through a rigid mount and turns the footage to jelly. Fix: add a damped mount, or hold the camera by hand.
• Shooting silently indoors at 1/1000 second and finding stripes later. The lights were flickering and the rear screen was too small to show it. Fix: take a test frame and zoom in, then use a mains-matched speed.
• Expecting the editor to straighten everything. Repair tools correct a uniform slant from a steady pan. They cannot rebuild a bent propeller or a rippling frame. Fix: solve vibration and rotation at the time of shooting.

Try this

Measure your camera’s readout time. Allow fifteen minutes. You need a mains-powered light that flickers: an older fluorescent tube or an inexpensive LED bulb is the most likely to work, and you may have to try two or three.

1. Select electronic (silent) shutter, manual exposure and 1/2000 second. Raise the ISO until a plain wall lit by the lamp looks mid-grey.
2. Fill the frame with the wall and take a picture. If there are no bands, try another light.
3. Count the dark bands from top to bottom, estimating any partial band at the edge.
4. Divide the count by the flicker rate (100 on a 50 Hz supply, 120 on a 60 Hz supply). Six bands at 120 per second means a readout time of 6/120, or 1/20 second.
5. Switch to the mechanical shutter and shoot again. You should see a gradient or a single partial band.
6. Finish with a doorway: in electronic mode, swing the camera briskly past the door frame, then repeat with the mechanical shutter and compare the lean.

Frequently asked questions

Does a faster shutter speed reduce rolling shutter?

No. Shutter speed sets how long each row is exposed, not how long the camera takes to get from the first row to the last. A faster speed removes blur, which makes the lean or bend easier to see.

Is rolling shutter the same as motion blur?

No. Motion blur smears a subject because it moved during the exposure of each row. Rolling shutter changes the subject’s shape because different rows were recorded at different moments. A frame can show both.

Do mechanical shutters cause rolling shutter?

Yes, a little. At fast speeds a focal plane shutter exposes through a moving slit, so rows are recorded at slightly different times. The curtains cross the sensor in a few thousandths of a second, so the effect is usually too small to see.

Can rolling shutter be fixed in editing?

Partly. Most video editors include a rolling shutter repair effect that corrects the even slant from a steady pan, and a still image with a uniform lean can be straightened with a skew transform followed by a crop. Wobble and bent rotating objects cannot be reliably repaired.

Related guides

• Mechanical vs electronic shutter: choosing between the shutter modes in the menu.
• Flicker and banding under artificial light: shutter speeds that are safe under mains lighting.
• High-speed sync: using flash while the shutter is a travelling slit.
• Global shutter: the definition of the design that reads every pixel together.
• Camera settings for video: frame rate and shutter choices that affect how motion looks.
• Image stabilization: what steadies the image before it is read, and its limits.