Rolling Shutter and Flicker Quiz: Artifacts and Solutions

A rolling shutter sensor reads pixel rows sequentially from top to bottom rather than capturing the entire frame simultaneously. Any subject movement during this scan causes the image to record different moments at different positions in the frame.

When a camera pans rapidly, each row of the sensor captures the scene at a slightly different time. Vertical lines, such as building edges or poles, appear slanted because the camera has moved between the moment the top row and the bottom row are read.

An electronic shutter reads the sensor row by row, so fast motion is recorded at slightly different times across the frame, causing skew. Under flickering lights, those rows catch the light at different brightness levels, producing horizontal bands.

A global shutter captures all pixels at exactly the same instant, eliminating the time-based skew that rolling shutter introduces. Every part of the frame records the same moment, regardless of how fast the subject or camera is moving.

Mains-powered lights such as fluorescents and many LEDs brighten and dim twice per AC cycle, 100 times per second on 50 Hz power and 120 times on 60 Hz. At fast shutter speeds, each frame catches the light at a different point in that cycle, so brightness and color vary across a sequence.

Arena lights flicker at twice the mains frequency. With a fast shutter, the exposure catches the lights at different points in the flicker cycle, so frames, or parts of a frame, vary in brightness and color, causing banding.

Anti-flicker mode detects the light source's cycling frequency and waits for the brightness peak before releasing the shutter. This ensures each frame is exposed at the same point in the flicker cycle, producing consistent exposure across a burst.

An electronic shutter reads the sensor row by row, and on many sensors that readout is fairly slow. A mechanical shutter's curtains cross the sensor much faster, so the time gap between the top and bottom of the frame is shorter and rolling shutter skew is reduced.

Many cameras disable or limit flash with an electronic shutter because the sensor is read row by row too slowly for all rows to be exposed when the flash fires. The flash sync speed is therefore slower than with the mechanical shutter, if flash is allowed at all.

A faster sensor readout reduces the time between reading the first and last pixel rows. The shorter this interval, the less the subject moves during the scan, and the smaller the spatial distortion introduced by the rolling shutter effect.

LED signs are often dimmed using pulse width modulation, switching on and off very quickly. With a fast shutter or an electronic shutter, the sensor catches parts of the sign mid-cycle, producing bands or missing colors.

Lights on AC power flicker at twice the mains frequency: 100 times per second at 50 Hz and 120 times per second at 60 Hz. A shutter speed that spans whole flicker cycles, such as 1/50 or 1/100 at 50 Hz and 1/60 or 1/120 at 60 Hz, averages the flicker out.

On 60 Hz power, lights flicker 120 times per second. Shutter speeds of 1/60, 1/120 and 1/240 second each cover whole flicker cycles, or line up with them, so each frame gets about the same amount of light. Speeds like 1/50 and 1/100 suit 50 Hz regions instead.

Rolling shutter distortion is worst when the sensor takes a long time to read all its rows and the subject or camera moves a lot during that time. A static subject on a tripod shows virtually no rolling shutter artifacts.

Because a global shutter captures all pixels simultaneously, there is no time gap between rows and therefore no positional error from subject or camera movement. Fast pans, propellers, and vibrating structures all render without the characteristic skew of rolling shutter sensors.