How does converting a video to 4K actually work?

Upscaling software is getting better all the time, but there are still some caveats to be aware of.

The shift from analogue film to digital video happened quickly. Before you knew it, tape-based video recorders had been replaced with digital video cameras and, later still, smartphones. 4K is now the gold standard for video creation, with 1080p left as its lower-quality sibling.

Despite widespread 4K adoption, there's still plenty of video being created in 1080p. And that's not to mention content made in the past, from home videos to old movies, available in standard definition or even lower. That can lead you to thinking about converting video to 4K, giving it a boost to make it look as sharp on a modern 4K OLED display as something you'd shoot today. Converting a video to 4K is possible, but it's a process with a lot of steps and points to consider first.

When we talk about 4K and 1080p, or ultra-high and high definition, we're talking about the amount of pixels contained within each video frame. For ultra-high definition video content, which is what most people usually mean by 4K, that means a resolution of 3,840 x 2,160 pixels , versus 1,920 x 1,080 pixels for 1080p high definition video. Standard definition video, meanwhile, sits at either 480 or 576 vertical lines depending on your region; width can vary depending on how the content was originally filmed. You can also find cinematic 4K resolutions , so-called 'true 4K' or DCI 4K, with a resolution of 4,096 x 2,160.

You can upscale any output file to 4K — 4K is just the frame size. To move from 1080p to 4K, you're going to need three additional pixels on-screen for every original pixel that was recorded, so four times overall. Managing that without losing any quality is the issue. That is almost impossible and simply changing the resolution won't reveal a hidden version with extra clarity or sharpness, either.

Traditional upscaling software uses interpolation to manage this, scaling up each frame and figuring out what it should look like. How accurate upscaling software can be is the main question. It has to estimate what the pixels should look like, but it can't recover the real detail if it wasn't recorded in the first place.

Often, this means that sizing up will make the footage look softer. The "guess-timation" used to add extra pixels often makes it look smooth as a result. Sharpening can help around the edges, but it's a Goldilocks dilemma: too much, or not enough, can ruin it. The same is true for noise reduction , which can make the final footage look unnatural.

If you're a professional looking to convert a video to 4K, you're going to want to work from the best source data available to you: the original source files. The better that source data is, the better quality a job you'll be able to achieve.