What's 4K? And does it matter for video games?

What is 4K resolution?

The size of an image is known as its resolution, and it's expressed in pixels. Similar to the way you'd describe a printed photograph as, say, a "four-by-six" image, resolution is typically listed in width times height. The PlayStation 4, Wii U and Xbox One can all output video at 1920x1080 pixels, or "1080p" for short, while most games in the previous console generation ran at somewhere near 1280x720, or "720p." (The "p" stands for "progressive," which is shorthand for "progressive scan," a technique in which a display draws every line of a single frame sequentially, from top to bottom, within the space of a single refresh cycle.)

The term "4K" can be a bit confusing, since the way it's used most often is technically a misnomer. For starters, you can think of a 4K image as one that has a width of somewhere near 4,000 pixels and a height of somewhere near 2,000 pixels. In the film industry, 4K refers to an image that is 4,096 pixels by 2,160 pixels, which is exactly twice the width and height of the 2K film standard; it's wider than the normal widescreen aspect ratio of 16:9.

In the world of television, the 4K video standard is called "ultra high definition," which builds on the terminology for 720p ("high definition") and 1080p ("full high definition"). The video industry seems to have settled on calling it "4K ultra HD" — or simply "4K" for short, since the full name is a mouthful. The width and height of an ultra HD image are exactly twice as large as those of a 1080p image, so the resolution of 4K ultra HD video is 3,840 by 2,160 pixels. (Following the existing naming convention, you might expect people to call this "2160p," but that doesn't quite roll off the tongue.)

For an easy way of understanding the increases in resolution from HD to ultra HD, let's do the math. A 720p image contains 921,600 pixels, while a 1080p image contains 2,073,600 pixels — 2.25 times as many. With a whopping 8,294,400 pixels, a 4K image is four times the size of a 1080p image and nine times as big as a 720p image. (Note that in the illustration below, the 1080p rectangle takes up one quarter of the full 4K image.)

It's worth noting that even with the massive jump in pixels from 1080p to 4K, it's hard for most people to actually tell the difference in a side-by-side comparison. That comes down to the typical American living room and the limits of human visual acuity.

"If you get into the higher resolutions like 4K or 8K, there is an obvious difference [compared to 720p], but the difference is best appreciated when sitting close to the screen and the TV is larger than 55 inches," said Barry Sandrew, PhD, a digital imaging expert who is the founder, chief technology officer and chief creative officer of Legend3D, a well-known stereoscopic 3D and visual effects firm.

In the average U.S. living room, people sit approximately 9 feet from their TV. At that distance from a 50-inch TV, it's very unlikely for someone with 20/20 vision to be able to tell any difference between 1080p and 4K resolution, according to Chris Heinonen, a reviewer for the websites Reference Home Theater and The Wirecutter. Heinonen put together a calculator indicating that you'd need to sit no farther than 6.5 feet from a 50-inch TV to be able to see any benefits of 4K resolution over 1080p.

So you're saying I shouldn't bother buying a 4K TV?

That's up to you! It's your hard-earned money, after all. And as we noted at the start, prices have dropped low enough that if you're spending hundreds and hundreds of dollars on a high-end TV, you might as well throw in a little extra and future-proof your living room with a 4K display.

There's another factor: high-end TV features that are just as important as — or, arguably, more important than — resolution.

A TV's contrast ratio is a measure of the difference between how bright it can get and how dark it can get. A higher ratio is better, and top-of-the-line TVs use a feature called local dimming to reduce the brightness in areas of a screen that should be dark (like a room with the lights off), thereby improving the contrast ratio.

This year, some cutting-edge features are starting to make their way into mainstream TVs: high dynamic range and wide color gamut. In tandem, these technologies help expand the range and depth of colors that a TV can display. In other words, a TV that supports HDR and wide color gamut can show hues that current TVs are literally incapable of displaying.

TV manufacturers have put a lot of effort over the years into marketing buzzwords in an attempt to push customers to upgrade their TVs. But TV reviewers who have seen HDR content say that it's the real deal, that it makes a palpable difference.

We should note here that only the latest version of HDMI, HDMI 2.0a, supports HDR. Not all HDMI ports are created equal; on some TVs, different HDMI ports might be of different version numbers. So if you want the latest and greatest tech, make sure to check your TV's HDMI ports before you buy.

Cool! So how can I fill all those pixels?

To be clear, anyone buying a 4K TV in 2016 still qualifies as an early adopter. As is usually the case with technology upgrades, the content side of the equation hasn't caught up to the hardware yet.

Television channels are still being broadcast in 720p or 1080i. Hollywood is just beginning to release movies on 4K Blu-ray; only a few dozen are available right now. The discs are expensive, and what's worse is that you'll need to upgrade to a 4K Blu-ray player to play them. Streaming services like Amazon Prime, Netflix and Vudu do offer a growing library of 4K content, and devices like the Roku and Amazon Fire TV — only the latest versions — can output 4K video. Microsoft's upcoming Xbox One S will support 4K video playback and HDR, the first gaming console to do so.

If you got excited by reading about HDR above, we'd warn you not to get ahead of yourself. There's much less content available in HDR at this point than in 4K, and again, streaming services are your best bet — Amazon Prime started offering HDR content last year, and Netflix joined the party this past spring.

Plus, there's a format war brewing for this nascent technology: HDR is available in an open standard called HDR10, and a proprietary one from Dolby Laboratories called Dolby Vision. Most TVs with HDR support HDR10, while a few manufacturers are also supporting Dolby Vision. So far, Microsoft has only confirmed HDR10 for the Xbox One S.

Basically, there is very little content out there right now that will take full advantage of 4K resolution, let alone all the additional technologies built into high-end 4K TVs.

OK, but what about video games?

That's the biggest wild card in all of this, isn't it?

As we explained in our graphics primer a couple of years ago, the resolution that a game can pump out depends on the power of the graphics processing unit (GPU), which is, of course, fixed for developers of console games. It has become clear in the years since the PlayStation 4 and Xbox One launched that the former contains more powerful hardware than the latter. Most PS4 games run in native 1080p resolution, while many Xbox One titles run at a lower resolution (such as 900p) that the console then upscales to 1080p.

Neither the PS4 nor the Xbox One currently upscale games to 4K, let alone run them natively at that resolution. Remember that running a game at 4K would require a console to generate four times as many pixels as a 1080p image; there's no way either system could handle that task.

On the PC gaming side, you'll need some of the latest graphics cards from AMD and Nvidia to achieve a reasonable frame rate (30 frames per second) at 4K. And even Nvidia's new top-of-the-line GeForce GTX 1080 can't reach 60 fps in the most demanding modern games, according to the company's own benchmarks. Gaming in native 4K resolution is such a challenge that you'll need a dual-GPU setup if you want to reliably hit 60 fps.

Therefore, it seems unlikely that the PS4 "Neo" or the Xbox One "Scorpio" will be powerful enough to run games natively in 4K. It's much more probable that they would be capable of upscaling games to 4K, in addition to running 1080p games at higher, more stable frame rates. And since both existing consoles use Blu-ray Discs, it's possible that their upgraded versions will be able to play 4K Blu-rays and output 4K video from streaming services.

All of this is to say that the state of video games and home video is always in flux, but rarely as much as it is right now. If you already have a 4K TV, it's starving for 4K content. If you don't own one yet, you may soon have many more reasons to buy one.

Update (June 21): This article has been updated to reflect the 4K and HDR support in the Xbox One S console.