The Math Behind the Rolling Shutter Phenomenon | Hacker News Reader

The Math Behind the Rolling Shutter Phenomenon

petapixel.com

81 pointssoundsop13 comments

Excellent article.

I remember a few years back holding my mobile to the window to take a photo of the scenery while on a turbo prop passenger aircraft. I nearly had a heart attack when I noticed the propeller had stopped spinning!

Once I got over the initial shock and realised it was just rolling shutter on the phone screen I had a bunch of fun taking photos and videos of the effect in action. I'll try and dig up one of the videos and post it here later.

It's especially fun when it's a helicopter and the camera is synchronized with the rotor:

https://youtube.com/watch?v=qgvuQGY946g

The rotor "freezing" is not caused by the rolling shutter, but by the rotor speed being an integer multiple of the framerate. In fact, you can see in the video you linked that the camera used does not have a rolling shutter.

Isn't that also true of the comment I replied to, though?

Yes, for the "propeller stopping" part, but they also mention "playing with the cool effects", and since mobile phones almost universally have rolling shutters, it's likely they did see it.

While in the video you linked it's very clear that it's a non-rolling shutter, which makes sense since most consumer-level cameras with video and that level of zoom use CCD sensors with electronic shutters, whether it's a camcorder or a " superzoom" camera.

Edit: since helicopter rotors turn much slower than propellers, you get a less cool effect of just bending the blades like in this picture: https://i.imgur.com/phTJtCd.jpg

Yes that's a very good point - the freezing of the blades is due to temporal aliasing, not rolling shutter. Here's a link to a post I made about this that includes a video showing both temporal aliasing and rolling shutter in action: https://plus.google.com/+ChrisMiller/posts/iAfeK4D7E9B

That's wonderful, the combination of the two effects in that video is really cool.

Excellent article. Presumably at least part of the problem toward the end is that it's based on the assumption the propellor moves at a constant speed; since the plane is not mid-flight, I would guess it's probably accelerating.

Hi, I wrote this article about a year ago on my blog. Thanks for posting it!

Horizon, a game based on rolling shutter mechanics, but with geometry instead of pixels: http://omershapira.com/portfolio/horizon-a-4d-game/

Wow. Terrific post- it is finding these kind of Gems that keeps me coming back to HN.

Here's some information about a different type of shutter, and camera, and imaging technology: http://www.largeformatphotography.info/forum/showthread.php?...

previous discussion (such as it was): https://news.ycombinator.com/item?id=8475255

Reply on news.ycombinator.com