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This picture has been floating around the internet recently:

enter image description here

Is it a genuine picture or photo-shopped? Or perhaps its some sort of optical illusion similar to the wagon wheel effect?

Sklivvz
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David says Reinstate Monica
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1 Answers1

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It's an effect of the camera's rolling shutter.

In many cameras, the image sensor doesn't capture the entire scene simultaneously. Instead it samples from its pixels row by row. Objects that move between samples may appear distorted across the image.

Here's a paper that describes the typical rolling shutter sampling process and the resulting image geometry.

This article has a lot more details on the rolling shutter effect. Further down the article, when it mentioned (s=1), shows the effect being captured by the above photo:

enter image description here

Nelson
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    See also: [What is a rolling shutter? When do I have to be aware of it?](http://photo.stackexchange.com/q/9523/32270) – Cole Tobin Apr 23 '16 at 17:55
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    If I understood properly, in this case it seems it's column by column, not row by row: http://i.stack.imgur.com/SPjCX.jpg – Oriol Apr 23 '16 at 22:37
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    PetaPixel have a really good article [The Math Behind the Rolling Shutter Phenomenon](http://petapixel.com/2014/10/13/math-behind-rolling-shutter-phenomenon/) which draws on this blog [post](http://danielwalsh.tumblr.com/post/54400376441/playing-detective-with-rolling-shutter-photos) – ThunderFrame Apr 23 '16 at 22:58
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    Most likely this particular picture was taken with a cellphone camera oriented vertically. At least on the iPhone, the rolling shutter goes row-by-row when the phone is held horizontally, and column-by-column when it's held vertically. – N. Virgo Apr 24 '16 at 02:44
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    It's also an artifact created by a focal plane shutter when the camera's shutter speed is set higher than its flash sync speed. Most DSLRs (and interchangeable-lens mirrorless cameras, as well as recent film SLRs) use a vertically-travelling focal plane shutter. Since the picture is in "portrait" orientation, that "vertically-travelling" shutter is moving horizontally. Google "focal plane race car" (without the quotes) to see that the effect isn't new, nor does it necessarily have anything to do with pixels (at least not before the silver prints are scanned). – Stan Rogers Apr 25 '16 at 02:51
  • +1. I'm a sports photographer by trade and can attest to this. There's no other plausible explanation for this oddity. This is shot at 1/8000s on my DSLR, notice the uneven spacing between the fan blades: http://i.stack.imgur.com/AUX7T.jpg – bwDraco Apr 25 '16 at 04:18
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    There's also [this simulation](https://www.desmos.com/calculator/yc9znckbcg) of the effect. – Joey Apr 25 '16 at 04:59
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    This answer is correct, but it might be useful to add something to the effect of "The image is real, but the propeller isn't actually bent" at the beginning just to make the answer a bit more clear and explicit. I'd propose the edit, but there's already a pending edit right now. – reirab Apr 25 '16 at 16:40
  • @Joey that's an awesome simulation also that site is pretty interesting. Thanks for the further details – khakiout Apr 26 '16 at 09:58
  • I happened to have taken a video of this effect in a Dash 8 a few years ago. However, I can confirm that there was no mechanical malfunction: https://www.youtube.com/watch?v=7zpT-8uv3G0 – Matthew FitzGerald-Chamberlain Apr 26 '16 at 20:40
  • In @Joey's simulation link, I get a very similar result by setting **w = 0.5, v = 0.33, t = 1** – doppelgreener Apr 27 '16 at 11:45