
Rolling Shutters - hazz
http://jasmcole.com/2014/10/12/rolling-shutters/
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zorpner
Nice! Whenever I see rolling shutter photos on flickr/etc I always think about
this old page where a fellow built a long-distance camera from a flatbed
scanner to get the effect intentionally:
[http://www.sentex.net/~mwandel/tech/scanner.html](http://www.sentex.net/~mwandel/tech/scanner.html)

(There's a great image of a garage door opening & closing about 2/3 of the way
down the page if you don't feel like reading the whole thing.)

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err4nt
This is so fascinating. This makes me long for the days when browsing
somebody's homepage on the web felt like they were actually inviting you into
their home like a friend.

~~~
mikepurvis
His woodworking videos are fantastic. Also, FWIW, he's now got a whole page
about the cameras he's used to film them:

[http://woodgears.ca/misc/best_camera.html](http://woodgears.ca/misc/best_camera.html)

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pbnjay
It's a neat analysis from a mathematical perspective, but (especially for a
rotating component like this) wouldn't the lighting be all wrong for the
remapped pixels? The slow-speed scanning examples use a fixed image (note the
highlight doesn't change) so it's likely not usable for real-world digital
photography without updates to account for lighting.

~~~
coldtea
Why would it be wrong? The pixels have the correct lighting (assuming the
overall ambient light didn't change during the rotation), just the wrong
position.

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ygra
They have the correct lighting _at their current position_ (the propeller was
actually at that point in the image when the photo was taken). Which means
when you transform them you'll get wrong lighting in the severely bent parts
because they rotated elsewhere when the picture was taken. Light shines on it
from another side and you cannot fix that just by changing the image
transformation. It's not the ambient light, but the directional part.

~~~
coldtea
A yes, the directional light (highlights, specs etc) would change...

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britta
Ha, my friend used the same photo as the example for his mathematical analysis
of the rolling shutter effect:
[http://danielwalsh.tumblr.com/post/54400376441/playing-
detec...](http://danielwalsh.tumblr.com/post/54400376441/playing-detective-
with-rolling-shutter-photos)

The questions he investigated: "Can we figure out the rate at which a
propellor is spinning by analyzing this kind of photo? And can we figure out
the real number of propellor blades in the photo?"

~~~
alexqgb
You can play a more complex version of that game using video of the vibrating
strings on a musical instrument. Here's an especially good example:
[http://vimeo.com/4041788](http://vimeo.com/4041788)

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salimmadjd
Sony is making steady advancements in the global shutter with CMOS sensors. A
bit harder on DSLRS with larger sensors and more pixels to read but the
smaller sensors with smaller megapixels already have them [1]. So it's matter
of a time that most CMOS bases videos will be free of rolling shutter,
starting with higher-end video cameras that have sensors with just enough
pixels to cover 2k-4k videos [2]

[1] [http://www.sony.net/Products/SC-
HP/new_pro/december_2013/imx...](http://www.sony.net/Products/SC-
HP/new_pro/december_2013/imx174_e.html)

[2] [http://www.newsshooter.com/2014/09/11/io-
industries-4k-super...](http://www.newsshooter.com/2014/09/11/io-
industries-4k-super-35mm-the-ultimate-action-camera/)

~~~
tonylemesmer
Couldn't help posting this (uses a Sony global shutter sensor):

[http://scolton.blogspot.co.uk/2014/05/grasshopper3-mobile-
se...](http://scolton.blogspot.co.uk/2014/05/grasshopper3-mobile-setup.html)

If it were possible to get this in a consumer grade video product I would be
very happy. Unfortunately these sensors are $1295.

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themgt
Somewhat relatedly, check out this awesome new camera technology which
essentially captures a rolling diff of the image rather than the image itself,
with impressive results:
[https://www.youtube.com/watch?v=LauQ6LWTkxM](https://www.youtube.com/watch?v=LauQ6LWTkxM)

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Fuzzwah
I see this effect happening in skydiving videos quite often.

The rolling shutter is also why stills from gopro videos never quite live up
to how clear the videos look in motion.

The cover photo from this month's parachutist magazine is a great example:

[http://parachutistonline.com/sites/all/files/images/cover201...](http://parachutistonline.com/sites/all/files/images/cover201410.png)

Notice the right leg of the jumpsuit, its flapping in the wind as the shutter
rolls over the scene.

When people use the slow-mo feature for gopro videos everything kind of morphs
rather than moving naturally. I've always found it to be a cool effect:

[https://www.youtube.com/watch?v=dUSF6xmmqJg&t=46s](https://www.youtube.com/watch?v=dUSF6xmmqJg&t=46s)

~~~
runeks
> The rolling shutter is also why stills from gopro videos never quite live up
> to how clear the videos look in motion.

I've thought about this as well. I always assumed the lack of clarity of
single frames extracted from video material is because the eye/brain
incorporates several images shown really quick in succession into one whole
image. So when only a single frame is shown, there's not as much information
in that as, say, 10 frames shown quickly in succession.

~~~
photoGrant
That's also because of the 'shutter speed' or 'shutter angle'. Basically each
frame stays 'open' for a certain amount of time to let the light in. Anything
slower than say 1/500s is going to introduce motion blur into the frame.

Shutter Speed/Angle are also creative choices. Anything that is faster than
1/50th (180 degree shutter angle) will introduce a 'staccato' effect to the
video. Anything slower will be mushy/blurry.

Somewhat off topic, but interesting nontheless!

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andmarios
A very cool article, indeed; but I believe he uses the term exposure wrong.

Exposure is the total time our whole light sensitive area is exposed to the
light coming from our scene. You can think of it as an integral of the sensor
(or film) area exposed as a function of the time, divided by the total sensor
area.

In the examples he uses the term exposure to describe the total scantime of
the sensor, whilst it seems that his actual exposure (which is equal to the
time each row of pixels samples the scene) is much smaller.

It may sound as a small difference but if one wants to reproduce the effect,
we will essentially need to match two parameters: exposure and scantime. While
exposure is easy to set, scantime is pretty much hardcoded and depends on the
physical characteristics of the camera. Even an analog shutter has a scantime
on small exposure times.

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kitd
If I understand this correctly, it is effectively doing what a photo-finish
camera does at race sports events, except that the slit moves across the
scene, rather than the scene moving past the slit.

Photo-finish shots also end up looking pretty weird:
[http://coachdeanhebert.files.wordpress.com/2007/08/100-photo...](http://coachdeanhebert.files.wordpress.com/2007/08/100-photo-
finish.jpg)

~~~
mhb
And the performance of those photo-finish systems is impressive. I would be
grateful if someone could explain how the software is able to almost
instantaneously identify the runners who are frequently not in lanes and also
often have missing numbers. For one example, see FinishLynx
([http://www.finishlynx.com/](http://www.finishlynx.com/))

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Magi604
I can see it now. Soon Adobe will include some tool or setting in Photoshop
that will automagically "fix" rolling shutter.

~~~
oakwhiz
I seem to recall that Adobe Premiere Pro and/or Adobe After Effects contain a
tool for mitigating rolling shutter artifacts, though I am not certain if it
uses the method described in the article.

~~~
abirkill
YouTube's stabilisation option attempts to remove (with reasonable success, in
my experience) rolling shutter wobble caused by camera movement, although I
don't believe it will mitigate the effect of a moving subject.

There was a talk at last year's Google I/O with some examples:

[http://youtu.be/QdXugkXBTbc?t=15m56s](http://youtu.be/QdXugkXBTbc?t=15m56s)

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carsonreinke
Awesome animated GIFs, definitely helps explain the concept.

This effect was manipulated to extract more information for this:
[http://newsoffice.mit.edu/2014/algorithm-recovers-speech-
fro...](http://newsoffice.mit.edu/2014/algorithm-recovers-speech-from-
vibrations-0804)

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GuiA
Definitely check out other articles on the author's blog; he's a great
technical writer.

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sp332
My favorite rolling-shutter video, of an upright bass:
[http://vimeo.com/4041788](http://vimeo.com/4041788)

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kordless
The radial graph half way down the page reminds me of this:
[http://en.wikipedia.org/wiki/Ulam_spiral#mediaviewer/File:Sa...](http://en.wikipedia.org/wiki/Ulam_spiral#mediaviewer/File:Sacks_spiral.svg)

~~~
arh68
Well that's certainly interesting. I was about to say, it reminds me
_strongly_ of a zeta function, in a way. But it turns out Dedekind's _eta_
function was what I was thinking of [1]

[1]
[https://en.wikipedia.org/wiki/Dedekind_eta_function#mediavie...](https://en.wikipedia.org/wiki/Dedekind_eta_function#mediaviewer/File:Discriminant_real_part.jpeg)

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Sami_Lehtinen
Rolling shutters were also used by traditional cameras. This effect is really
old school stuff. Rolling shutter providers better exposure than circular
shutter. I remember that most of professional photographs taken in 80s also
used rolling shutter.

~~~
rimantas
You mean curtain shutters, which become just a slit traveling across the
sensor at short exposures? I am pretty sure modern DSLRs still use them.

