Much like 1080p Full HD technology before it, ‘4K’ has certainly captured the attention of industry as well as the general public, leading to a lot of uncertainty of what it actually means to video systems. Here, Kordz founder David Meyer answers the big questions on 4K and offers you a sneak peek at HDMI 2.0.

4K is an exciting and necessary development in the world of electronic displays. Unlike 3D, which is really just a novel side-step feature, 4K defines a whole new level of detail and immersive realism on the screen. But it’s still early days and the industry is generally still on a learning curve.

As a member of both CEA’s 4K Working Group and CEDIA’s Technology Working Group as HDMI subject matter expert, and co-author of their upcoming 4K whitepapers, I regularly get asked a lot of questions on the topic. The most common ones are:

•    Why do we need 4K?
•    What’s the difference between 4K and Ultra HD?
•    What about content? Citing “no point without native content”.
•    Will my current ‘HDMI 1.4’ device support 4K?
•    Will current HDMI cables support 4K?
•    What’s happening with HDMI 2.0?

Let’s take at look at these questions, and more…

Why do we need 4K?
The answer to this question is actually quite logical. Screen sizes have gotten a whole lot bigger on average over the last several years, but viewing distances have generally not increased. There was a time when we thought a 34” CRT TV was massive, and when flat panel displays came along, 42” became the norm. These days, 55-60” is most common for general living rooms, with a growing catalogue of even larger sizes from the big CE brands.

As screen sizes get bigger without changing resolution or viewing distance, the pixels too become relatively larger. There comes a tipping point where our own visual acuity may exceed the display’s pixel density, meaning an effective loss of perceived resolution. Now give some thought to IMAX, which employs a massive screen and the audience sitting relatively close. Achieving this high quality immersive experience is made possible with the use of a much larger film cell than is the case in a classic 35mm cinema (see Figure 1).

4K delivers the same effect in the home, enabling larger screens with relatively close viewing distances.

There is another consideration; that being the marked increase in resolution of the other devices we typically use every day. 1080p was regarded as remarkable back in 2005 but is, after all, only 2MP (1,920 x 1,080 = 2,073,600). Let’s face it, these days you’d turn your nose at a 2MP camera in a phone! By comparison, 4K offers a far more contemporary 8.3MP. Enough said.

What’s the Difference Between 4K and Ultra HD?
Nothing. Let me explain. The name ‘4K’ was derived from the commercial D-cinema space, being a SMPTE defined standard for a 4,096 pixel horizontal resolution (Hres) image. This evolved from 2K before it, being 2,048 pixels wide. Display hardware needs physical pixels, so commercial 4K display devices (e.g. DLP projectors) employs 2,160 vertical pixels (Vres), while 2K is 1,080 Vres, the latter being the same as for consumer 1080p.

In 2009, HDMI Licensing announced the HDMI 1.4 specification which first defined 4K formats for broader use, including consumer, with HDMI as the transport.

This included two formats:

•    4096 x 2160p    (24fps only (SMPTE, aka D-Cinema))
•    3840 x 2160p    (23.98/24/25/29.97/30fps (16:9))

Three years later in 2012, the CEA, via its 4K Working Group, targeted a consumer friendly moniker for this new format, as evolution from Full HD (1080p). Ultra HD was the result, and is in fact interchangeable with the term 4K, or 2160p. It’s the same thing.

For the record, expect to see the 3,840 Hres version dominate, as it retains the same standardised aspect ratio of 16:9 or 1.78:1 as does 720p and 1080p. 4,096 may be offered in some high end product only, as is the case with Sony’s flagship VPL-VW1000ES projector.

What About Content?
It is valid at this point to reference the age old dilemma of which came first – the chicken or the egg? Think back to the early days of 1080p. Do you remember that? The first few generations of devices comprised only upscaling DVD players and the occasional AVR doing the same. Arguably none did it well as superior images did not result, only increased bandwidth demands on a not-yet-matured HDMI. It took until about 2006 when HD DVD and Blu-ray came along with native 1080p content, finally giving way to Blu-ray as victor in 2008.

That’s now so long ago that we seem to have conveniently forgotten that necessary step to evolve a new format. With 4K we get to do it all over again, but expect it to all happen a whole lot faster. For one thing, 4K actually has a head start on where 1080p was at the same point in its infancy, as there already exists an impressive back catalogue of titles, both through rescanning/mastering and also native capture. That is, movies being shot in 4K. All we’re now waiting on is at least one ratified source platform.

The Blu-ray Disc Association (BDA) is already working on the next version of the BD specification. This is rumoured to be quite lateral in its approach, paving the way for inevitable development of both 4K High Frame Rate (HFR) and even 8K formats. They clearly don’t want to have to come back and re-do it all over again in a couple of years! Stay tuned.

When questioning if there’s any point to 4K without content availability, consider that content providers would not release titles unless there were displays available to support it. The displays must come first, followed by source devices, concurrent with content. The first steps are already well advanced with an impressive offering to market at typically early adopter prices. They will inevitably come way down.

Will my current ‘HDMI 1.4’ device support 4K?
4K was every bit as much a part of the HDMI 1.4 specification as was 3D, Audio Return Channel (ARC) and HDMI Ethernet Channel (HEC). The poor practice of most CE device manufacturers a few years ago to reference their products as “HDMI 1.4” was done so to declare their support for the then headline features of 3D and ARC. 4K was without exception NOT supported. That’s precisely why HDMI Licensing banned the practice of referencing version numbers – it was and still is uninformative and irrelevant.

There are hardware HDMI bandwidth implications in being able to fundamentally support 4K video. This is covered in greater detail in the ‘HDMI Bandwidth for 4K’ section further on in this article.

Will current HDMI cables support 4K?
Yes… well, maybe. 4K as it stands now requires approximately 9Gbps aggregate data rate through HDMI. High Speed HDMI cable should be certified to 10.2Gbps, so theoretically it’s good to go, right? The reality is that HDMI has actually been cruising to date, as we’ve generally been using only 4.5Gbps out of the 10.2Gbps available. With 4K we’ll finally start to really use the capacity of High Speed HDMI, so you’d better make sure your choice of cables really are what they say they are.

But, many claiming to be High Speed actually aren’t. There are two reasons for this:

1.    When the new Standard and High Speed labelling was introduced in 2010, it was accompanied with advice that you need Standard HDMI for 720p/1080i, and High Speed for 1080p. That led to a misconception that 1080p and High Speed were the same thing. At 4.455Gbps and 10.2Gbps respectively, clearly they are not. Many cables claimed to be High Speed simply because they worked at 1080p. HDMI compliance at 4K is a whole other story.
2.    High Speed simply sounds a whole lot sexier than Standard. If you were in marketing, which would you use? Many reputable brands did not succumb to such practices, but many did.

The bottom line is, when it comes to choosing cables, stick with a vendor you know and trust to be able to assure you that 4K will be supported. You do not need a new ‘version’ cable for 4K support. Nothing has physically changed in the HDMI cable specification since 2003, other than the optional addition of the HDMI Ethernet Channel, which has nothing to do with 4K. It all comes down to bandwidth supported by the individual products. Don’t assume you need a new cable, and for the purposes of giving interoperability its best fighting chance, try to always stick with native HDMI cabling.

What’s Happening with HDMI 2.0?
There’s been a lot of chatter about HDMI 2.0 for some time now. The good news is that it’s real, it’s happening and it’s not too far away.

It is far too early to reveal specifics, but here are a few facts:

•    In the past, HDMI was always evolved by its Founders and HDMI Licensing, LLC. HDMI 2.0 is different in that it’s in the hands of HDMI Forum, Inc, a separate non-profit organisation comprising more than 70 members.
•    HDMI 2.0 will be an addendum of HDMI 1.4, and both specifications will continue concurrently for the foreseeable future, with full backwards compatibility,
•    The headline feature of the new HDMI specification will 4K High Frame Rate (HFR), being up to 60 frames per second. I estimate this will yield a Clock speed of 594MHz, which is nearing 18Gbps in applied data rate. The days of passive HDMI cables are numbered.

COME TO THE 4…K
Further to the six common questions addressed above, there are some other elements to 4K that are also well worth exploring.

In no particular order, they are as follows.

HDMI Bandwidth for 4K
If you take nothing else away from this article, remember this – 297MHz HDMI Clock, or 8.91Gbps data rate. They’re the minimum numbers you need for 4K support in devices and cables alike. To appreciate what this really means, it may help to compare these numbers to what HDMI enabled devices have been using to date.

The very first ever HDMI enabled devices back in 2004 contained HDMI chipsets – transmitters, repeaters or receivers – that could support 165MHz, or 4.95Gbps. This was surprisingly enough for 1080p right out of the gate (1080p60 is 4.455Gbps). Since then, all devices ever since the release of HDMI have fundamentally had the chipset capacity to support 1080p. Not as much has changed as you may think! The rest came down to resolution, firmware and features, etc of individual products.

With the 2006 release of the HDMI 1.3 specification, Deep Colour was the headline feature, spawning a new generation of HDMI chipsets that increased Clock to 225MHz and data rate to 6.75Gbps aggregate. This unlocked the ability to go to uncompressed 12-bit Deep Colour. To this day most devices in the market are still employing 225MHz HDMI silicon.

4K up to 30fps requires 297MHz, or 8.91Gbps. If current devices are using 225MHz HDMI chipsets, clearly that’s not enough. New hardware is required as the bottleneck is literally in the silicon. Firmware updates alone won’t cut it.

4K TVs will all have at least one HDMI input using the new generation 300MHz HDMI chipsets, as introduced by some leading semiconductor manufacturers from last year. Also, expect this to be just one of the new additions to Sony’s upcoming PS4 as well, among many other things. In time 300MHz will be ubiquitous, just as 225MHz was from 2007 onwards.

However even 300MHz can only support up to 4K at 30fps. To get the more ideal 60fps (also encompassing 4K 3D), the next step will likely be 600MHz, or 18Gbps. That’s 180 times faster than the best theoretical connection proposed by the multi-billion dollar NBN, and HDMI needs to deliver it in real time. That’s serious numbers.

Colour Depth
It’s worth noting that HDMI already supports 10- and 12-bit colour without any bandwidth premium with YCbCr 4:2:2 (Blu-ray) and 4:2:0 (DVD) formats. But if we’re talking uncompressed (RGB or 4:4:4), then 10-bit comes with a 25% premium, and 12-bit with a 50% premium over standard colour. That’s okay when we have supplied headroom in the HDMI chipsets, as we do currently with 225MHz for 1080p.

With 4K there’s no room to move. We need 297MHz as a minimum, but the chipsets are just a nudge above that at 300MHz. That means 4K30 will only be offered in 8-bit uncompressed colour, but 10- and 12-bit will still be available for compressed YCbCr formats. That’s all in theory based on current standards – we’ll wait and see what the Blu-ray Disc Association do with the BD specification.

Frame Rate
Frame rate is every bit as important as resolution when talking about bandwidth. However, it is often the neglected appendage, the geek speak that hangs off the end of what the marketers like to really focus on. As an example of how important frame rate is, consider that 720p60 actually has more active pixels per second than 1080p24. Frame rate matters.

First generation 4K will be limited to 30fps, half that of what we commonly use for 1080p(60). 4K is four times the resolution of 1080p, but being only half the frame rate is why it can fit into double the bandwidth, not four times. HDMI 2.0 will bring to the table 60fps, so at that point bandwidth really will quadruple over 1080p60. Hang on!

Conclusion
4K is a logical evolution in HD video, finally offering a serious upgrade path from the long matured 1080p. 2MP just doesn’t quite cut it anymore, particularly as TVs have got progressively bigger, making screen size-viewing distance ratios smaller. 4K, in conjunction with evolving display technologies like OLED, is the answer to our growing demands for size and quality.

HDMI is the ubiquitous standard for digital HD connectivity. For it to deliver 4K video system-wide, all HDMI chipsets in the signal path need to support at least 297MHz Clock, or 8.91Gbps data rate. Look for anything above these numbers in the product tech specs. HDMI cables need to be demonstrably High Speed. In fact, with 4K we’ll finally start to use High Speed HDMI for the first time ever, really finally challenging HDMI connectivity.

“With Ethernet” is irrelevant.

A few years from now we’ll look back and wonder what all the fuss was about with lack of content. It really is not a hindrance, rather a necessary step to delivering full-system 4K video performance.

It’s coming. It’s real. It’s awesome. Be ready.