8
\$\begingroup\$

My friend recently took a picture with her tablet of two boys riding a bicycle while she was in a moving car. When she viewed the picture, the background was very clear and the bicycle and the lower part of the boys could be seen but the heads of the boys could not be seen. She somehow convinced that she captured ghosts (hehe).... Please help me explain this to her in technical/photography perspective.

enter image description here

I have attached the specific picture that is in question. I look forward hearing some expert explanation.

Improve this question
\$\endgroup\$
5
  • 1
    \$\begingroup\$ If this wasn't a tablet I'd blame a rolling shutter \$\endgroup\$
    – SailorCire
    Commented Apr 5, 2015 at 13:16
  • 3
    \$\begingroup\$ Tablets can also encounter the rolling shutter effect if the the sensor is read out sequentially rather than all at once. \$\endgroup\$
    – Michael C
    Commented Apr 5, 2015 at 19:15
  • 1
    \$\begingroup\$ Perhaps the phone app was in panorama or HDR mode? \$\endgroup\$
    – Fer
    Commented Apr 7, 2015 at 21:16
  • 1
    \$\begingroup\$ Perhaps they were having a out of body experience, and their heads were elsewhere? \$\endgroup\$
    – Olin Lathrop
    Commented Dec 25, 2016 at 15:05
  • 1
    \$\begingroup\$ This is most probably an HDR issue. Which brand of tablet was used? If I remember correctly, an iPad would also store the individual exposures as well as the combined image in the photo library. \$\endgroup\$
    – Pete
    Commented Sep 13, 2019 at 10:25

3 Answers 3

Reset to default
18
\$\begingroup\$

Rolling shutter looks like the most obvious answer but I'd say it is a red herring.

With rolling shutter the cyclists would not be cut in half as they are, they would be bent or warped through their full length, all of which would be in the frame. As would other objects in the frame. The wheels would also show signs of extreme geometric distortion in the spokes which doesn't seem to be the case.

Even accepting a read/burst break caused the behaviour - the point at which they're cut is not straight, nor does it run horizontally (or even straight) in the image. Nor is it applied across the full width of the image - I'd expect a similar cropping to occur with the tree on the right which again is not the case there.

On closer inspection the rider's hand is cropped lower than the rider and passenger's bodies - the cut is not horizontal across the image as well as not being straight.

Having ruled out the only photographic option we need to look elsewhere. That means the image was produced in software, either deliberately by the user or by an app on the tablet. So what might that be is speculation since the image doesn't give us absolute proof.

I see a tearing effect across the passenger and rider. Plus, where the riders hand is cut, it is rounded rather than square. This points me in the direction of an edge-detection algorithm. Probably one built for cutting and combining multiple images perhaps intending to create a sharper image. Similar effects can be seen on 360 degree images built from multiple exposures like Photosynth where the processing system can't quite work out the joins or if people/objects move between shots.

This process is probably built into the camera app and would not have been done by the user. If an option to control the behaviour exists at all it's unlikely to be obvious that it would create this output, so the user wouldn't know what was happening they just press the button and get the picture out.

TL;DR

It's not a photographic issue or artifact. Some software was trying to make the picture look nice and ruined it.

Improve this answer
\$\endgroup\$
7
  • \$\begingroup\$ Thank you all for your reply. . Thank you James for a detailed explanation. However, my friend doesn't have any photography nor editing skills. She took that picture with the built in camera on her tablet and that's how the picture turned out to be. :) \$\endgroup\$
    – eyestones
    Commented Apr 5, 2015 at 21:12
  • \$\begingroup\$ I'll update the answer to address that point. \$\endgroup\$
    – James Snell
    Commented Apr 5, 2015 at 21:19
  • \$\begingroup\$ Done now. Your friend didn't do it, the software in the tablet did it for them without them having to do anything. \$\endgroup\$
    – James Snell
    Commented Apr 5, 2015 at 21:32
  • 8
    \$\begingroup\$ Might be some kind of "HDR" setting in the photo app which took three pictures at different exposures but failed to combine them into a single image because the cyclists moved between the shots. \$\endgroup\$
    – Roman Reiner
    Commented Apr 6, 2015 at 7:18
  • \$\begingroup\$ Perhaps a 'panorama' setting that matched two or more (almost) identical scenes, at least one without the bikers. \$\endgroup\$
    – BobT
    Commented Sep 6, 2016 at 3:05
14
\$\begingroup\$

This is very likely the result of an automatic HDR mode.

Because of the apparent high contrast of the scene, the camera app tried to blend multiple pictures of the scene with different exposures together.

Due to the fast movements in the scene, not all of these source pictures contained the cyclist, and so it's only visible in parts.

I know from experience that some camera apps (like the one from iOS) will automatically switch to HDR-Mode if the scene-contrast calls for it.

A rolling shutter looks different

A rolling shutter would cause geometric distortion, like in the following picture. (The shutter speed was around 1/5800 (electronic shutter) and I moved the camera to follow the cat.)

Rolling shutter due to camera movement and very high shutter speed

Please note that I added this picture only as an example, not for it's quality or artistic value ;)

Improve this answer
\$\endgroup\$
-1
\$\begingroup\$

This is due to the "rolling shutter" effect. See this video for a somewhat nauseating example, or this description with great graphics.

Basically, at this exposure setting, not all the image is scanned in one instant, but rather in stripes, so that the bicyclist was not in the frame for the whole duration (though the background, farther away, was visible for the full exposure).

Improve this answer
\$\endgroup\$
2
  • \$\begingroup\$ Do you still have one on an electronic shutter? \$\endgroup\$
    – SailorCire
    Commented Apr 5, 2015 at 21:52
  • \$\begingroup\$ It's not only a physical shutter, but the scanning of the sensor that causes the "rolling shutter" effect (which is why I put it in quotes). There are too many pixels to be output in parallel, instantaneously, so the array is serialized... repeatedly. \$\endgroup\$
    – DrMoishe Pippik
    Commented Apr 6, 2015 at 0:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.