Why does a digital photo of an image on a tv screen appear to have moving waves of pixels as you zoom in, shouldn’t the pixel placement be fixed in a still photo?

Question

I took a photo of a show that I had paused on my flatscreen television (or computer screen), and when I looked at the picture it had gray lines of pixels. It almost looked warped, but as I zoomed in those lines changed and disappeared. As I zoomed in and out I saw that the gray lines moved away like a wave and the image became more clear and less clear respectively. Shouldn’t the gray lines be permanent in a photo, why does zooming change the actual captured image and not enlarge the flaw? Try it your self.

In: 4

Answer 1

What you’re seeing is called a Moiré Pattern. It happens when the captured Image contains a grid (in this case a grid of pixels), as well as the thing in front of it is another grid (your display’s pixel layout), but they don’t align perfectly.

[Relevant XKCD](https://m.xkcd.com/1814/)

[and wiki article](https://en.wikipedia.org/wiki/Moir%C3%A9_pattern)