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In answer to another question, Adam Davis writes:

Your camera complicates this by using a rolling shutter above a given speed (usually around 1/200. This means that only a portion of the image sensor is exposed to the scene at any given time, so if the light changes during the exposure, the color change will only affect a portion of the image sensor.

Rolling shutters often are also mentioned in the context of DSLR videography. However, I am yet to see a discussion of what a rolling shutter is, how it works and when it is important.

What is a rolling shutter?

What are the implications of using one for my photos?

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    \$\begingroup\$ What Adam is talking about is not actually a rolling shutter, it's just a focal plane shutter. It also does nothing special above 1/200. \$\endgroup\$
    – thomasrutter
    Commented Mar 7, 2011 at 10:36

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What Adam is referring to

What Adam is talking about is not actually a rolling shutter, it's just a focal plane shutter. It also does nothing special above 1/200, except that the effect of the shutter curtain has some interesting properties which can become more pronounced at higher speed.

The diagrams on the wikipedia page (reproduced below) illustrate it best. Essentially the shutter consists of two curtains which move from top to bottom (or in some film cameras, left to right) in quick succession. The gap between them is what exposes the image.

Focal plane shutter, low speed

Focal-plane shutter, low speed. Black square is the sensor, red and green squares are the first and second curtains.

Focal plane shutter, high speed

Focal-plane shutter, high speed. Black square is the sensor, red and green squares are the first and second curtains.

If the shutter speed is fast enough, the second one will start closing before the first one has fully finished opening, so the entire frame won't all be exposed at once. Therefore, you get a situation where anything that happens really fast, like the flash of a camera or the oscillation of a fluorescent light, may cause light not to cover the entire frame but instead create bands or gradients from top to bottom where the light is different.

The diagrams show the shutters moving horizontally as they did in most 35mm mechanical film cameras, whereas modern cameras with electronically controlled shutters (film or digital) almost universally have vertical shutters. It's the same effect but in a ninety degree different direction.

What a rolling shutter effect is

The rolling shutter effect as it applies to digital video is quite a different and quite unrelated effect to the one described above. Actually, a rolling shutter effect does not actually involve a physical shutter, but it's called that as a convention because it is analogous to the way a film cinema camera has a shutter that moves across the frame. In digital video, the rolling shutter effect is the result of the way a CMOS sensor is read.

CMOS sensors exhibit a rolling shutter effect when they are in live view or video mode, in which they are being read for every video frame. Instead of capturing the entire frame at once, information is read from each row of the frame one after the other, top to bottom. The whole process takes up to 1/30 of a second on most cameras. This creates a jelly-like wobbling effect in recorded video when the camera is handheld or moves a lot.

In a given sensor, this rolling shutter happens equally regardless of the shutter speed, though with slower shutter speeds it may be less noticeable in subject movement because of the extra motion blur. The effect is not usually noticeable when the camera is fixed on a tripod or panned steadily, but is more obvious when the camera is hand-held or during fast camera movements.

CMOS sensors capable of higher frame rates than 30 frames per second (and not just through repeating frames) will exhibit less rolling shutter effect because their sensors will have been designed to be read faster.

CCD does not suffer from the rolling shutter effect.

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    \$\begingroup\$ Yep that's good, thanks. In case people are wondering, the diagrams show the shutters moving horizontally whereas modern cameras seem to have vertical shutters. Same effect though. \$\endgroup\$
    – thomasrutter
    Commented Mar 9, 2011 at 2:04
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    \$\begingroup\$ It may be worth noting that if a video that is shot with a rolling-shutter camera is shown on a CRT whose scan pattern matches that of the camera, the artifacts created by the rolling shutter will be reversed by the scanning action of the CRT. For example, a video of near-vertical lines moving from right to left would skew them so the bottom was shifted to the left, but a CRT showing a video of near-vertical lines would skew them so the bottom appeared shifted to the right. I don't know of any modern displays that try to accurately emulate such behavior, however. \$\endgroup\$
    – supercat
    Commented Nov 12, 2014 at 16:47
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    \$\begingroup\$ The Rolling shutter Wikipedia article disagrees with the opening sentences of the "What a rolling shutter effect is" section above. From WP: "Rolling shutter ... 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"; and, "the 'rolling shutter' can be either mechanical or electronic." \$\endgroup\$
    – scottbb ♦
    Commented Apr 26, 2016 at 22:55
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    \$\begingroup\$ Indeed, the classic "leaning" 1920's race car image is exactly a rolling shutter effect caused by a wiping shutter progressively exposing the scene from bottom to top. \$\endgroup\$
    – scottbb ♦
    Commented Apr 26, 2016 at 23:00
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    \$\begingroup\$ My answer is consistent with what you pointed out on Wikipedia. Where do you think the contradiction is? \$\endgroup\$
    – thomasrutter
    Commented Apr 27, 2016 at 4:10
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The rolling shutter is a method of image capture which is not by taking a snapshot of the entire scene at single instant in time, but rather by scanning across the scene rapidly (vertically or horizontally).

The implications of using a rolling shutter can produce predictable distortions of fast-moving objects or rapid flashes of light such as wobble (jello effects), skew, smear and partial exposure.

Few examples:

A photo of a Eurocopter EC-120

The rotor blades seem to be swept back more than usual due to the rolling shutter effect.

lighting

A photo exhibiting partial exposure. Lighting conditions changed between the exposure of the top and bottom parts of the photo.

picture by The Slow Mo Guys

Shadow of champagne cork shows that it already hit the face, however cork is still suspended in the air.

This back-in-time phenomenon can be explained by the following animation (where changing colour indicates a shutter rolling vertically from the top to the bottom):

champagne cork blasting into the face by The Slow Mo Guys

Here is demonstration by The Slow Mo Guys how a rolling shutter works based on Canon EOS 7D:

a rolling shutter in slow motion

Related:

See more:

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    \$\begingroup\$ Except that champagne cork sequence was shot using video with the mechanical shutter open the entire time - and since the image is inverted on the sensor, the sensor scans from the bottom to top of the sensor (top to bottom of the inverted image). If it was taken using the mechanical shutter in "stills" mode, the cork would be way ahead of the shadow because the bottom of the frame (top of the sensor) would have been exposed first. Please see here for more detail about this specific test. \$\endgroup\$
    – Michael C
    Commented Jan 28, 2018 at 22:20
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Adam's terminology is slightly out - you don't get a rolling shutter above 1/200s or so, but one whose where the bottom edge starts to close before the top edge has fully opened, but the effect is the same (a rolling shutter implies the scene is constantly read out from top to bottom).

Effectively what you get at high speeds is a slit that moves up the sensor exposing one part at a time. This has implications for large changes in lighting during the exposure, such as flash, or in the original context florescent lights which vary during the AC cycle.

Lots of related questions for further reading:

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  • \$\begingroup\$ No, a rolling shutter doesn't imply that the image is read repeatedly. \$\endgroup\$
    – Guffa
    Commented Mar 7, 2011 at 15:13
  • \$\begingroup\$ Doesn't it? see my comment on your answer! \$\endgroup\$
    – Matt Grum
    Commented Mar 7, 2011 at 16:46
  • \$\begingroup\$ The name of Ottomar Anschutz' internal focal plane shutter invented in 1883 was the "internal roller blind shutter". This was for still cameras, not movie cameras. Prior to that rolling shutters were placed in front of the lens. The term has been around a long time. \$\endgroup\$
    – Michael C
    Commented Jun 5, 2016 at 2:56
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This movie on youtube is the best explanation of this I've seen.

I discovered it on this page on DYI photography site

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  • \$\begingroup\$ You might also want to watch this explanation on YT \$\endgroup\$
    – Gerhardh
    Commented Jul 27, 2017 at 22:36
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The shutter is actually two shutters, one that slides up and one that slides down. One is used to start the exposure and the other one is used to end the exposure.

It takes a little bit of time to open a shutter, so if there was only one shutter there would be a difference in exposure time between the top and the bottom of the image. If for example the shutter needs 1/1000 s. to open, that would mean a 20% difference in exposure time between the top and the bottom when exposed at 1/100 s.

The term rolling shutter is used when the second shutter starts to close before the first shutter has finished opening. In the extreme case this means that there is just a thin opening that rolls across the film/sensor. You could get the same function from a single shutter in the form of a curtain with an opening that rolls across the media, but that construction would give you less flexibility when it comes to exposure times.

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    \$\begingroup\$ I would disagree on the terminology, rolling implies something is constantly happening in a cycle, such as a rolling roster or rolling substitutes in sport, and as such only applies to repeatedly reading the image line by line electronically as in live view, not to the operation of a mechanical shutter. \$\endgroup\$
    – Matt Grum
    Commented Mar 7, 2011 at 10:07
  • \$\begingroup\$ @Matt Grum: This, for example, disagrees with you: en.wikipedia.org/wiki/Rolling_shutter \$\endgroup\$
    – Guffa
    Commented Mar 7, 2011 at 15:09
  • \$\begingroup\$ That's Wikipedia for you, the article seems to contradict itself on the subject: "This method is implemented by rolling (moving) the shutter across the exposable image area instead of exposing the image area all at the same time (the shutter could 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 increasing sensitivity." How can the image sensor continue to gather photons using a mechanical rolling shutter? \$\endgroup\$
    – Matt Grum
    Commented Mar 7, 2011 at 16:43
  • \$\begingroup\$ n.b. I didn't downvote you, the rest of your answer contains useful info, despite a difference of opinion of the definition of rolling... \$\endgroup\$
    – Matt Grum
    Commented Mar 7, 2011 at 16:59
  • \$\begingroup\$ Wikipedia likes to contradict itself sometimes. See also the article on the focal plane shutter which at no point refers to it as a "rolling shutter" en.wikipedia.org/wiki/Focal-plane_shutter - amusingly they even include the same helicopter image as an example of a focal plane shutter effect. I think, and this is what I personally feel, that it's a common misconception that that is what a "rolling shutter" is. \$\endgroup\$
    – thomasrutter
    Commented Mar 8, 2011 at 0:14

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