ELi5: Why is that when you photograph a television or phone screen, the picture shows squiggly lines all over the screen?

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This “lines” aren’t really visible when you’re just looking at a screen. I’m not sure if this has something to do with the resolution of the screen, or perhaps even quality of camera, but I’ve taken pictures of multiple TV screens while they were on. Each came out with some kind of distortion.

In: Technology

3 Answers

Anonymous 0 Comments

You might be seeing something called a moire pattern – it’s caused by two grids (in this case, the tv pixels and the camera pixels) being slightly different scales.

Anonymous 0 Comments

It is more down to the human eye than the camera. Most people cannot really detect flickering above 40hz, a certain percentage can perceive above 60hz and some crazy people with training can see much higher (like over 150). Most screens (TVs and pc screens) are 60hz refresh rate so when we look at them we see a smooth picture. Now we if there was a missing frame 1/60 we could probably see it or notice it at least. What we don’t notice is that screens refresh from left to right and even older ones refresh left to right, line by line from bottom to top. So basically when you take a picture it is a snapshot of the screen refreshing itself and so certain parts of the screen are showing a slightly different picture, which makes things appear out of line. The camera picks up what we generally cannot.

Edit: I should say for modern LED screens the pixels refresh all at the same time. However they will be ever so slightly out of sync due to manufacturing Torrance’s etc. The same thing as above applies though. What we see and what the camera picks up on is slightly different.

Anonymous 0 Comments

The sensors in the human eye (rods and cones) do not form a grid. Nor do we actually just capture a single image but instead the brain tapes together a bunch of pictures into one persistent one. A camera uses a grid of sensors to capture a single still image. Now the grid is almost always going to be a different size that that of the grid on the screen so what happens is similar to when you look through one window screen to another or two different chain link fences at the same time.