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Ultra HD and 4K explained: Everything you need to know & what you can watch

Nathan Spendelow David Ludlow Lee Bell
5 Jan 2017
Sky Q 4K David Attenborough
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Find out everything you need to know about 4K, Ultra HD and UHD Blu-ray

While 4K has been with us for a while now, it's now starting to seep into our homes en masse. With 4K TV prices hitting lows of £500, there's no better time to make the jump, with more and more people feeling the benefits of Ultra HD and 4K resolution. But what really is 4K and Ultra HD resolution, why should you care and what are the best 4K films to watch right now?

Find out the best 4K TV's you can buy right now

Below you'll find the definitive guide to Ultra HD and 4K, pointing out the differences between the two, the benefits over Full HD resolution and explaining why High Dynamic Range (HDR) is the hot thing right now.

What’s the difference between Ultra HD and 4K?

The terms Ultra HD and 4K have been used interchangeably, with the latter the more popular term by far. However, in terms of home entertainment, 4K is technically an incorrect term, as it refers to the cinema standard, which has a resolution of 4,096 x 2,160 pixels. The home standard is Ultra HD, which has a resolution of 3,840x2,160 to match the 16:9 aspect ratio of TVs. For the purposes of this article, we’re talking about Ultra HD.

Everything you need to know about Ultra HD Blu-ray is here

What does Ultra HD give you that Full HD doesn’t?

The simple answer to this question is more resolution. While Full HD TVs have a resolution of 1,920x1,080 (a total of 2,073,600 pixels), Ultra HD TVs have a resolution of 3,840x2,160 (a total of 8,294,400 pixels). In other words, Ultra HD TVs have four times the resolution of standard Full HD TVs, with each picture equivalent to a shot from an 8-megapixel camera. That’s a massive increase of resolution, which means that with the right footage 4K TVs can show more detail than is possible with a Full HD TV.

A couple of images can help show the differences between the various technologies. First, I’ve got the traditional image that shows the difference in size between images, starting with regular PAL TV at the bottom left and moving up to Ultra HD. As you can see Ultra HD is a huge jump from Full HD.

Ultra HD vs HD vs 720p vs SD

The issue I have with this image is that it shows the differences between images when they’re displayed at full resolution on a 4K TV. Obviously, in real life if you had a 4K TV and watched Full HD content, the image would be full-screen. A better comparison, in my view, is to compare Full HD and 4K TV at the same physical size, which I’ve done in the images below. These are frames pulled from the open source film, Tears of Steel. For these comparisons, I downloaded the rendered frames from the 1080p and cinema 4K versions of the film. I resized the cinema 4K version to fit the Ultra HD standard. I cropped the images at the same point, so that you can see the differences more clearly.

Tears of Steel Full HD crop
Tears of Steel Ultra HD crop

When viewed at the same size, the Full HD version (top) is noticeably softer than the Ultra HD version (bottom). In particular, the Ultra HD version has much better skin texture and you can more clearly read the writing on the carton. You can argue that the differences are subtle, but the effect is greater when watching Ultra HD content: it looks sharper and once you’re used to it, Full HD tends to look soft. Resolution is just one aspect of Ultra HD, though, with the new standard making a few other improvements.

Better colour and a higher frame rate 

One of the main things that hasn’t changed with higher resolution TV is the frame rate we watch content at, with films traditionally shot at 24fps and UK TV at 25fps. With Ultra HD that changes and the technology supports up to 60fps (UK TV will most likely come in at 50fps – double the existing frame rate). There may be some naysayers out there saying that a higher frame rate makes footage look wrong and films look as though they’ve been shot on video, but they’re completely wrong. The smoother footage looks a lot better and removes any jerkiness from fast-moving scenes or panning shots. It’s particularly useful in sport, as you can more easily keep up with the action.

On top of that standard gives better colour depth with support for 10-bit and 12-bit colour, rather than the 8-bit colour available at the moment. That means a wider range of colours are available, which gives a more vibrant and realistic colour palette, as well as bringing out subtler detail in images. There’s also the promise of High Dynamic Range (HDR) footage.

Ultra HD and 4K: What is HDR?

The dynamic range in content describes the ratio between the darkest and lightest shades of an image. Typically, an image or a film is shot with a relatively low dynamic range, which means you lose some detail in one part of the image. For example, you may have lots of detail in the shadows of an image, but little detail in the sky; conversely, shadows may appear black, while the brighter part of the image may have lots of detail. With HDR footage, you get all of the detail in the dark parts of the image and all of the detail in the lighter parts of the image. We’ve seen this technique used in photography a lot and now most smartphones even have an HDR photo mode; however, this is the first time that the process has moved into video. We’ve seen some test footage and it’s looking stunning. Find out more by reading our guide to HDR TV.

Exodus Gods and Kings HDR

Ultra HD and 4K: What about sound?

There’s no maximum or minimum sound quality set in the Ultra HD standard, but you can get everything from stereo audio up to 7.1 lossless Dolby TrueHD and DTS-HD Master Audio soundtracks, depending on the source footage. In other words, you can get amazing sound, but the source of the footage defines the quality and type of soundtrack.

Doesn’t Ultra HD footage take up loads of room?

You need a lot more storage space and bandwidth to deliver Ultra HD footage, but not as much as you think. While current Full HD footage generally uses the H.264 codec, Ultra HD content is typically encoded using the H.265 codec, also known as High Efficiency Video Coding (HEVC). It needs a lot more processing power to deal with, but cuts file sizes down: it can make files roughly half the size as when using H.264. Unfortunately, outside of computers, which have powerful processors and are easy to upgrade, HEVC support can’t be added retrospectively to older products. That means, for example, that Ultra HD Netflix support can’t be added to an older TV or media streamer except via an external box.

What are mastered in 4K Blu-rays?

You may have seen that there are a growing number of Sony-produced Blu-ray discs that say Mastered in 4K on them. Given that most films are shot in at least 4K, this sounds like common sense, but there’s actually a couple of differences that are quite important. First, the discs have been created directly from the 4K or higher original masters, which should give a cleaner and clearer picture. Sony has also said that the compression used takes advantage of the X-Reality Pro processors in its TVs to make for better upscaling when you watch the discs on an Ultra HD TV. While you may getter slightly better results than watching a regular disc, the results are still a way off a native Ultra HD image.

More importantly, the new discs use the x.v.YCC colour specification; if you’ve got a TV and Blu-ray player, such as the PlayStation, that support this colour space, you’ll get better colour definition from these discs. Ultimately, Mastered in 4K is really just a method of improving original Blu-ray and you won’t get the full image quality and colour range as with true Ultra HD.

See the next page for the latest info on true Ultra HD Blu-ray.

Mastered in 4K

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