Rolling Shutter Explained

When a camera captures fast movement it can result in strange artefacts becoming visible due to the exact time at which the camera’s sensor samples the light coming through its lens.

There are two main ways in which a camera samples the scene: 

• Rolling Shutter
• Global Shutter

Rolling shutter samples different points of the image at different times (left to right, top to bottom). They are easier/cheaper to implement as light falling on the sensor has the longest time possible to build up charge. However as you’ll see in the videos below, they can result in very odd artefacts.

Global shutter cameras result in a true snapshot of an image with all pixels representing the same moment in time. Global shutter is typically found in high-end/broadcast cameras.

Prior to the introduction of CCD sensors all broadcast cameras used scanning electron beam based camera tubes (3 separate  tubes for RGB colour). These would sample the light falling on the imaging plane in much the same way as the rolling shutter method discussed in the above videos. When CCD-based cameras were introduced in the 1980’s (which used global shutter style of capture) they could result in artefacts that were particularly visible on vertical edges when the camera panned – when viewed on a CRT display the vertical edges would appear to be slanted – very similar to the artefacts we now see with vertical edges captured with a rolling shutter when displayed on a on a modern flat-panel display!

See Wikipedia for more information about old-fashioned camera tubes,