What is 4K Blu-ray?

What is 4K Blu-ray?

4K standards and terminology

The term "4K" is generic and refers to any resolution with a horizontal pixel count of approximately 4,000.[5](p2) Several different 4K resolutions have been standardized by various organizations.

DCI Digital Cinema System Specification

Comparison of DCI and UHD resolutions

In 2005, Digital Cinema Initiatives (DCI), a prominent standards organization in the cinema industry, published the Digital Cinema System Specification. This specification establishes standardized 2K and 4K container formats for digital cinema production, with resolutions of 2048 × 1080 and 4096 × 2160 respectively.[6](§4.3.1) The resolution of the video content inside follows the SMPTE 428-1 standard,[6](§3.2.1) which establishes the following resolutions for a 4K distribution:[7](p6)

  • 4096 × 2160 (full frame, 256∶135 or ≈1.90∶1 aspect ratio)
  • 3996 × 2160 (flat crop, 1.85∶1 aspect ratio)
  • 4096 × 1716 (CinemaScope crop, ≈2.39∶1 aspect ratio)

2K distributions can have a frame rate of either 24 or 48 FPS, while 4K distributions must have a frame rate of 24 FPS.[6](§3.1.4.2) Some articles claim that the terms "2K" and "4K" were coined by DCI and refer exclusively to the 2K and 4K formats defined in the DCI standard.[8] However, usage of these terms in the cinema industry predates the publication of the DCI standard,[9][10][11][12] and they are generally understood as casual terms for any resolution approximately 2000 or 4000 pixels in width, rather than names for specific resolutions.[5](p2)[13](p109)

Ultra HD 4K Blu-rays have the best picture quality possible for your 4K TV, even better than streaming 4K from Netflix or Amazon.

Even better, many discs have high dynamic range (HDR) and wide color gamut (WCG) content, which provide a much more noticeable improvement than 4K resolution, provided your TV can deliver it.

"But I hate physical discs," you say. I hear you. But for people who want peak image quality, a disc is still the way to go. And for new and current movies, it's often cheaper than you'll pay for streaming.

The industry has learned from its past mistakes, at least a little. 4K players will all play standard Blu-ray discs and DVDs as well, for example. There's also only one format! No UHDDVD or other such nonsense. All the manufacturers are on board for a single unified format, so the great Blu-ray vs. HD-DVD format war is ancient history.

How is it different from regular Blu-ray?

There are plenty of interesting features that differentiate the two. It's like the companies behind Blu-ray are throwing everything into 4K with either a "Yeah, let's do it right!" or "OMG streaming will kill us all!" mentality.

4K UHD resolution: Standard Blu-ray discs are high-definition 1080p resolution, but the new ones will fill every pixel of your new 4K (ultra high-definition) TV with sumptuous detail. Of course 4K resolution is often difficult to discern from 1080p, many movies weren't captured in 4K to begin with and most graphics aren't in 4K either. Even so, the 4K Blu-ray is typically the highest-resolution version of that particular film currently available.

Expanded color: Thanks to advancements such as OLED and quantum dots, a much wider color gamut is possible in many modern TVs. The problem is, they'll need expanded color gamut content for this feature to be useful. That's where 4K Blu-ray discs come in. The 4KBD format has the ability to do the full extent of the Rec. 2020 standard in the future, though only the smaller DCI's P3 color range is available on today's discs. Either one is a big improvement over the current HD standard used on standard Blu-ray, Rec. 709, which dates back to the dark ages (of CRT). For background info, check out Ultra HD 4K TV color, part I and Part II. For the current tech, check out: What is wide color gamut?

High dynamic range: Most 4K Blu-rays have HDR data. HDR is really cool. It means brighter highlights, expanded contrast ratios and more, on TVs that support it. Read more about it: How HDR works.

hdr-tv-03.jpg

Most 4K Blu-ray discs are available with HDR.

Sarah Tew/CNET

10-bit: Both HDR and expanded color are possible, thanks to a higher bit-depth of 10, greater than current HD's 8-bit. At the very least, this means more steps of gradation -- no banding, not that Blu-ray had much.

Higher frame-rates: 4K at 60 Hz. Not a big deal, honestly, as nearly all movies are 24fps (and will certainly will be in their native frame-rate on 4K BD). Still, that leaves some headroom for future concert videos or if you want to torture your brain with the HFR "Hobbit."

H.265/HEVC: This is the latest codec, allowing 4K at "reasonable" bit rates. Technically, you could fit a 4K movie on a current Blu-ray disc (size-wise), but at that level of compression, what's the point? Instead, there will be...

Greater capacity discs: Most current Blu-rays are 25GB, some are 50GB. 4KBDs will be 66GB or 100GB. These discs won't play in your current player. Sorry.

Audio: Expect formats such as Dolby Digital and True HD in their respective variations, and DTS in its various flavors, will all be there. We'll also see Dolby Atmos and DTS:X.

Should you care?

4K Blu-ray faces a lot of competition from 4K streaming. Netflix

Though Blu-ray disc sales are still a big source of revenue for the studios, their popularity is rapidly declining. Netflix, Amazon and others offer 4K streaming, and most offer HDR content as well.

The fact is, most 4K Blu-rays will look significantly better than any streaming feed. The compression issues we've seen with HD are just as possible with UHD, though how it's compressed is different.

Sadly, most people won't care. Worse, most people won't know there's a difference. 4K is 4K to most people (and if you're reading this, I'm not counting you in the "most" group). That's a battle not likely to be won by an archaic physical media, no matter how shiny it's marketed as being. Think that's pessimistic? How many of your friends still watch DVDs?

samsung-ubd-k8500-05.jpg Sarah Tew/CNET

Will your current TV be able to take advantage of all this?

Maybe. Depends when you bought it.

At the very least your TV will need HDMI 2.0 and HDCP 2.2 to play the discs, and HDMI 2.0a to do HDR. (HDMI 2.1 is the latest, but that's overkill at the moment.) The HDR and WCG won't work on pre-2015 TVs, since those technologies didn't really exist then.

If you bought a mid-to-high-end 4K TV since 2015, it might work. Check the specs and see if it has the aforementioned HDMI and HDCP compatibilities. Your current HDMI cables should work.

Of course, you'll also need a 4K Blu-ray player such as the Samsung UBD-KS8500 (about $200, £210 or AU$200) or an Xbox One S (about $250, £200 or AU$290). More players are coming out in later in 2017 as well.

Bottom line

For picture-quality fans this new format is great. The resolution will be awesome on really big TVs, and the potential color and HDR aspects will be amazing on any size TV that can take advantage of it.

But it's never going to be as popular as Blu-ray -- we're too far into the streaming era for that. Hopefully it will tide us over until we all have ultrafast broadband and 4K streaming can actually look good.


Got a question for Geoff? First, check out all the other articles he's written on topics like why all HDMI cables are the same, TV resolutions explained, LED LCD vs. OLED,and more. Still have a question? Tweet at him @TechWriterGeoff then check out his travel photography on Instagram. He also thinks you should check out his bestselling sci-fi novel and its sequel.

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