from Hacker News

Rolling Shutters

by hazz on 10/12/14, 11:33 PM with 41 comments

  • by zorpner on 10/13/14, 2:07 AM

    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

    (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.)

  • by pbnjay on 10/13/14, 2:32 AM

    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.

  • by britta on 10/13/14, 2:46 AM

    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...

    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?"

  • by salimmadjd on 10/13/14, 2:55 AM

    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...

    [2] http://www.newsshooter.com/2014/09/11/io-industries-4k-super...

  • by themgt on 10/13/14, 7:59 PM

    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

  • by Fuzzwah on 10/13/14, 4:30 PM

    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...

    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

  • by andmarios on 10/13/14, 9:13 AM

    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.

  • by kitd on 10/13/14, 8:59 AM

    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...

  • by Magi604 on 10/13/14, 4:26 AM

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

  • by carsonreinke on 10/13/14, 1:19 PM

    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...

  • by GuiA on 10/13/14, 3:29 AM

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

  • by sp332 on 10/13/14, 7:36 PM

    My favorite rolling-shutter video, of an upright bass: http://vimeo.com/4041788

  • by kordless on 10/13/14, 3:43 PM

    The radial graph half way down the page reminds me of this: http://en.wikipedia.org/wiki/Ulam_spiral#mediaviewer/File:Sa...

  • by Sami_Lehtinen on 10/13/14, 6:36 AM

    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.