When a big image is down sized to fit the screen terrible cuts appear, it looks like pixelated, its worse when you watch photos of people, it deforms their faces, making an eye looking bigger than other for example.
It's easier to explain with pictures, so there it goes:
Note, I'm passing between 2 images, one the same size as the screen (1080p) and one bigger than the screen (5K), it's just an example, it happens with any image bigger than the screen size.
