Why is it so hard for a camera (iPhone camera at least) to take a solid photo of a screen?

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Always these weird lines

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3 Answers

Anonymous 0 Comments

Those lines really exist. Your screen is a grid of pixels made of red, green and blue dots that glow. Your phone has its own grid of light sensitive photosensors that react to red, green and blue.

No way are you going to get those grids just lined up. So the phone’s grid of pixels shows the monitor’s grid of pixels more clearly than your human eye does. There’s a reason every ad for a phone or computer says that “screen images are simulated” or such in the small print.

Seriously, people should stop trying to take photographs of screens. I don’t see this problem “going away” unless someone trains an AI to fix photos. If it’s your own computer, take a screenshot with the PrintScreen key or whatever tool your operating system offers and use that instead.

Anonymous 0 Comments

There are 2 things you might be referring to:

* The “miore,” effect. This happens when two grids overlap (you can see great examples by looking up images of “miore pattern.”) and produce a bunch of weird curved and criss-crossed lines. It can happen with chain-link fences, certain types of clothing, etc. For screens and digital cameras, it happens because the grid of pixels on the camera sensor are misaligned to the grid of pixels on the screen you’re recording, and so some double up, while some catch the small gap between pixels.
* The horizontal/vertical lines appear due to how the screen changes it’s brightness. A lot of screens use something called “PWM,” (Pulse Width Modulation) which is a fancy way of saying “flickers on and off really fast to trick your brain into thinking it’s dimmer.” Since cameras usually scan the sensor from top to bottom, it means that the camera is actually recording the screen at slightly different brightness levels in different parts of the image. It’s basically the same effect that causes [“rolling shutter effect,”](https://youtu.be/17PSgsRlO9Q?si=v_2SvieZLL-CNoQh) but with brightness levels instead of motion.

Anonymous 0 Comments

Its a mathematical principal called “[Moiré](https://en.wikipedia.org/wiki/Moir%C3%A9_pattern)”

When 2 grids have different cell size (or one is closer to an observer than the other), or are rotated, the dark parts of the grid overlap creating an extra dark spot.

Both screens and Camera’s use grids of pixels, since its almost impossible for these grids to be lined up with each other you get that effect any time you take a picture of a screen. Its basically impossible to get rid of, there are ways to reduce it (like making the space between pixels thinner, or increasing the resolution) but it will always be there.

Our eyes dont have this problem because the photo receptors in them are not arranged in a grid at all, just organically placed around (and our brain does an amazing amount of preprocessing our vision field (this is what your vision actually looks like https://xkcd.com/1080/)).