Global Shutter / Rolling Shutter

The two ways a camera can expose an image: all pixels at once, or row by row in sequence.

These are the two exposure and readout schemes an image sensor can use. A global shutter exposes all pixels at the same instant; a rolling shutter exposes and reads out row by row from top to bottom, with a time gap between rows. Many CMOS cameras use a rolling shutter because it is structurally simpler, cheaper, and more light-sensitive. But when photographing a fast-moving object, or when the camera itself is shaking, the image skews, warps, or judders — this is the “jello effect”; under a flash, only part of the frame may get lit. For robots, a wrist camera moving with the arm, or a legged robot’s body shaking while walking, means a rolling shutter introduces errors into SLAM, visual-inertial odometry, and camera calibration, which is why these scenarios often use a global-shutter camera instead, or model and compensate for the rolling shutter’s row-by-row time offset in the algorithm.

ExamplePhotographing a fast-spinning propeller with a rolling-shutter camera makes the blades come out bent or even broken up into strange shapes; a global-shutter camera doesn’t show this.

Also called

Global Exposure, Rolling Exposure, Jello Effect

Related

CMOS Image Sensor · RGB Camera · Visual-Inertial Odometry · Wrist Camera · Event Camera · Camera Calibration

Sources

Wikipedia: Rolling shutter