Why 1080p movies can look better than 4K movies on your TV

PabloLagarto/Shutterstock At first glance, the claim seems a bit absurd: how could a 1080p image look better than 4K, a resolution with four times as many pixels? Resolution tells you how many pixels are on the screen, but it doesn't tell you how much picture information survived compression before those pixels reach your TV.

Streaming services , for example, have to send all of those pixels through an internet connection; to avoid buffering, they compress the video. Your TV or streaming device then decodes the compressed video stream before it reaches your eyes on the display. But "decode" is not the same thing as "restore." The process of compression, sending and decoding demands a price, and that price includes discarded details like fine film grains, shadow transitions, texture details or complicated motion information.

The differences are usually easier to spot in difficult scenes filled with smoke, rain, moving leaves, huge crowds on the move and deep shadows. On the other hand, a 1080p Blu-ray preserves those same details more naturally and presents them better than a lower-bitrate 4K stream.

It helps to think of resolution as the size of a canvas, while bitrate is the amount of paint available to fill it. A 4K stream has a lot more canvas to work with, but it still needs enough data to fill it completely, with all the color changes and motion across millions of pixels, frame after frame. Major streaming services use adaptive bitrate delivery, a fancy way of saying they maintain multiple quality versions of a movie/show and switch them around based on network conditions. For 4K streaming, Netflix recommends a 15Mbps connection . However, that's just a recommendation. It's not a promise that every moment of every movie will make it through to your set at its highest bitrate.

Blu-ray has a much simpler job, because all it has to do is read from a local disc instead of adapting to an internet connection. Standard Blu-ray gives 1080p video up to 40Mbps to work with, while Ultra HD Blu-ray supports up to 108Mbps on 66GB discs and 128Mbps on 100GB discs. Of course, those are format limitations and not a guarantee for every title, but it's a good illustration of why discs can retain more fine information.

Then there is codec efficiency, which complicates the comparison even more. Modern streaming codecs, like HEVC, can do more with less data than older Blu-ray codecs. A strong 1080p encode will typically beat a struggling 4K stream because it has fewer pixels fighting for the available bitrate

TimeImage Production/Shutterstock There's a simple and tidy mathematical relationship between 1080p and 4k, which makes it easier for 4K panels to upscale 1080p so it can fill a 3,840 x 2,160 pixel grid. All the 4k panel has to do is take each 1080p pixel and form it into a 2 x 2 block of 4K pixels, though the finer details tend to suffer a bit. But since a 4K panel can certainly handle it, start by giving the TV the best source possible.

If you have a choice between a Blu-ray disc and a low-bitrate stream, choose the Blu-ray disc because it will look noticeably better.