Electronic shutter

Electronic shutter

Digital image sensors (both CMOS and CCD image sensors) can be constructed to give a shutter equivalent function by transferring many pixel cell charges at one time to a paired shaded double called frame transfer shutter. If the full-frame is transferred at one time, it is a global shutter. Often the shaded cells can independently be read, while the others are again collecting light. Extremely fast shutter operation is possible as there are no moving parts or any serialized data transfers. Global shutter can also be used for videos as a replacement for rotary disc shutters.

Image sensors without a shaded full-frame double must use serialized data transfer of illuminated pixels called rolling shutter. A rolling shutter scans the image in a line-by-line fashion, so that different lines are exposed at different instants, as in a mechanical focal-plane shutter, so that motion of either camera or subject will cause geometric distortions, such as skew or wobble.

Today, most digital cameras use combination of mechanical shutter and electronic shutter or mechanical shutter solely. Mechanical shutter can accommodate up to 1/16000 seconds (for example the Minolta Dynax/Maxxum/α-9 film camera had a maximum of 1/12000, a record in its era, and the later digital Nikon D1 series were capable of 1/16000), while electronic shutter can accommodate at least 1/32000 seconds, used for many superzoom cameras and currently many Fujifilm APS-C cameras (X-Pro2, X-T1, X100T and others).

Rolling shutter

A photo of a Eurocopter EC-120. Notice that the rotor blades seem to be swept back more than usual due to the rolling shutter effect.

Simulation of the rolling shutter effect on a rotating propeller and a moving car
(click for SMIL animation)

Rolling shutter is a method of image capture in which a still picture (in a still camera) or each frame of a video (in a video camera) is captured not by taking a snapshot of the entire scene at a single instant in time but rather by scanning across the scene rapidly, either vertically or horizontally. In other words, not all parts of the image of the scene are recorded at exactly the same instant. (Though, during playback, the entire image of the scene is displayed at once, as if it represents a single instant in time.) This produces predictable distortions of fast-moving objects or rapid flashes of light. This is in contrast with "global shutter" in which the entire frame is captured at the same instant.

The "rolling shutter" can be either mechanical or electronic. The advantage of this method is that the image sensor can continue to gather photons during the acquisition process, thus effectively increasing sensitivity. It is found on many digital still and video cameras using CMOS sensors. The effect is most noticeable when imaging extreme conditions of motion or the fast flashing of light. While some CMOS sensors use a global shutter, the majority found in the consumer market use a rolling shutter.

CCDs (charge-coupled devices) are alternatives to CMOS sensors, which are generally more sensitive and more expensive. CCD-based cameras often use global shutters, which take a snapshot representing a single instant in time and therefore do not suffer from the motion artifacts caused by rolling shutters.