10

I took a trip on a helicopter and took many pictures with my iPhone 6 plus. One of the images was distorted with a sort of wavy ripple blur effect (other images did not exhibit the same distortion):

enter image description here

I'm guessing this has something to do with the vibration plus some inage stabilization algorithm but can anyone provide a technical explanation of what's causing this?

  • 2
    Was this through a (plastic) window? Vibration patterns in its distortion combined with electronic readout speed perhaps? – Linwood Sep 19 '17 at 14:50
  • The window cannot be the cause since many other photos from this and other cameras have been taken through the same window, just moments before and after this one, and they exibited no distortion at all. – Stav Sep 20 '17 at 15:20
  • @Stav If the window is constantly changing shape due to vibration all of the images shot through it would not look the same. – Michael C Sep 21 '17 at 3:12
  • @michael it's not a different deformation each time, there simply isn't any deformation at all. – Stav Sep 21 '17 at 8:36
  • Then it must have been aliens. – Michael C Sep 21 '17 at 8:43
5

It looks like the rolling shutter interacting with the vibrations. It could be scanning horizontally, and the vibration comes in pulses. You could see it in a Big-Small-Big-Small pattern, from left to right.

  • This my theory as well. But I couldn't find hard evidence that the iPhone 6 plus camera scans this way and that it doesn't work with a global shutter. – Stav Sep 20 '17 at 15:23
  • @Stav well, the iPhone 6 pano seems to be leveraging the rolling shutter. That's why you can take pictures of "deformed" people in pano. – Calyth Sep 20 '17 at 15:58
  • This is not the shutter interacting with vibrations. The blurring is all wrong for being caused by vibration. You'd see the image being smeared in the direction of motion. The blurring looks quite uniform in all directions, like out of focus. Also, does the iPhone 6 even have a mechanical shutter? I expect not. – Olin Lathrop Sep 21 '17 at 12:01
  • Going to have to agree with @Olin here.. blur looks very uniform.. but do look at the regularity of the pattern at large, it simply doesn't make sense that this is something external.. – Stav Sep 22 '17 at 18:21
3

I don't think this has anything to do with the shutter, other than exposure was fast enough to freeze something that might otherwise be averaged out and therefore be less obvious.

I think there are two possibilities:

  1. Looking out thru a crappy plastic window.

  2. Looking thru the shockwaves from the propeller blades. The significant pressure difference in the shockwaves changes the density of the air, and thereby its index of refraction. The air then in effect becomes another lens between the camera and the distant subject.

    This is the same effect that causes mirages, just that those are more subtle and therefore require longer distances to become apparent. The downwash and shockwaves from helicopter rotor blades is much more violent. After all, the blades are pushing hard enough on the air to keep you and the whole machine up.

3

I can tell you it's not the window. I fly in helis a lot for work and we ALWAYS work with the doors off. I came upon this thread because I specifically went looking for the answer after having seen it on my own iphone photos from two different iphones, series 6s plus and 8 plus. I posited a similar theory to Calyth, that the downforce of the blade is changing the composition of the air, thereby creating a seperate "lens". Here is one I've taken that showed this phenomenon. Again, this aren't taken through any window as we always fly without doors. enter image description here

  • 1
    Wow, that really looks like a tilt-shift photograph — or else one with a "tilt-shift miniature" effect applied. – mattdm Jul 19 '18 at 21:04
  • No doubt. Honestly nothing at all done to it. I would add it couldn't be exhaust as we were moving forward at about 115kts. Strange how, in the case of this photo, like many I have, The banding of blur splits the frame. I'm lead to believe this is an effect of rolling shutter. – user76628 Jul 20 '18 at 17:03
1

It could be the shutter as per Calyth. However, Aircraft are fitted with plastic window material that is far from optically flat. Lots of distortion from these especially if curved. Additionally, lots of turbulence in the air surrounding the helicopter exacerbated by the hot exhaust mixed.

  • 1
    It's probably too uniform from top to bottom and in the way the separate bands are shaped from top to bottom to be thermal. – Michael C Sep 19 '17 at 20:06

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