what are those patterns we see when taking a picture of a screen?

Question

When taking a picture of a screen there are these weird lines that when viewing the pic in different sizes or resolutions causes different lines to appear

In: 6

Answer 1

You are probably seeing a [rolling shutter](https://www.youtube.com/watch?v=dNVtMmLlnoE) effect and the refresh rate of your screen. Let’s talk about digital cameras first. A digital camera works by having a chip with light-sensing components arranged like pixels in a screen. That’s where the *megapixel* number for a digital camera comes from: how many of these pixels does the chip have? The lenses focus the light onto the chip and each individual pixel senses light, or doesn’t, and records that.

However, that’s a *lot* of data and the camera can’t record it all fast enough. There are only so many channels that data can flow through to get to the drive where the images are stored. So, the pixels in the camera record more or less one at a time, but *so fast* that unless what you’re taking a picture of is also moving very quickly the camera will be able to record the scene before it has time to change. The pixels usually go from left to right, top to bottom.

Your screen also can’t really deliver data fast enough to update *every* pixel at the same time. Although the entire image may refresh at 60Hz or 30Hz or 144Hz, whatever your refresh rate is, it’s usually changing either one pixel at a time or maybe one line of pixels at a time. It may also do every other line first, then go back and do the lines it skipped: this prevents you from seeing the line with your eyes.

So, the camera pixels are saving the data as a wave traveling down the chip, and your screen is updating itself as a wave traveling down the monitor. When the two rates don’t match, at some point there will be some overlap where one has updated before the other can catch up and it creates a line.

With analog cameras, the film is exposed to light by a shutter opening. That action needs to be *very* fast, so the shutter probably doesn’t completely open and completely close all at once. Instead, a gap is opened and moved across the aperture. You can see it in [this gif](https://thumbs.gfycat.com/AchingFrigidArmyworm-max-1mb.gif) taken from a Slow Mo Guys video. This creates a similar effect, in that that film is exposed to light as the scene is “updating”.