Why do electronic screens look like they’re having a seizure whenever you take a video or a picture of them?
In: Technology
Because they are being refreshed a certain number of times per second.
The device you are using to record shoots a certain number of frames per second as well.
The chances of these rates aligning is very small.
Therefore, you might capture empty frames sometimes.
Also, screens are refreshed from top to bottom, or some other method. You might catch half a frame even.
To add to other comments, think of it this way.
The screen displays a certain number of pictures in a second. In between those it’s blanks (not quite but it’ll do). I’ll represent these images with an X and blanks with an O.
Your camera can also do the same, except the Xs represent the time it’s taking a picture.
But these rates are different
Screen
XXOXXOXXOXXOXXOXXOXXOXXOXXOXXO
XXXOOXXXOOXXXOOXXXOOXXXOOXXXOO
Camera
See how the Xs of the camera almost never line up perfectly to capture just the Xs of the screen?
I think the easiest way to think about it is a screen is basically showing you a bunch of pictures in a super quick succession like a flip book. A camera records footage in the same way. If the rate that the camera is taking those pictures isn’t the same as the rate that the screen is displaying them, you’ll get shots taken where the screen is in the middle of changing the image it displays. When you see those images in transition in super quick succession on another screen like a camera display or a later play back, you see them as flickers.
Same reason an airplane propeller seems to be moving forward, then backwards, then forward again as it spins up. Sync rate. You only actually see it part of the time (your eyes are too slow). Same thing with video, but the speed isn’t changing.
Tl;dr; because the camera is only capturing some of the screen changes.
* edited for spelling and punctuation.
As others have explained the refresh rate, and compared it to aircraft, here’s an example of a high speed camera’s frame rate syncing with a helicopter’s prop rotation rate.
[Copter](https://imgur.com/gallery/ewuPfh8)
/u/captiandisillusion to the rescue
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