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The sense and nonsense of Ultra HD 8K – viewing distance, sharpness and size

Ultra HD 4K is only a few years old, we are completely replacing our televisions, and Ultra HD 4K content is still available with little by little. And yet the next novelty is already on the doorstep. But how sensible is Ultra HD 8K really?

Is it really so new?

Before we take a look at the meaning of Ultra HD 8K in the living room, let’s take a look at the detail. Ultra HD 8K 7,860 by 4,320 pixels, is not just a new idea from screen manufacturers. The concept of a very high resolution has been around for a while in documents and standards of DVB (Digital Video Broadcasting) which are managed by the EBU (European Broadcasting Union).

This picture, which we made on a presentation by TP Vision in 2014 clearly shows the roadmap that broadcasters back then (and actually a few years before) had in mind.

Attention, this was the roadmap for TV services, the screens always run a bit for this timing. What we can already deduce from this roadmap is that UHD 8K was on the planning for 2020 and later.

Can we see all that detail?

That 8K screens can show an enormous amount of detail seems obvious to us. To put it in perspective: 8K is four times more pixels than 4K, or sixteen times more pixels than Full HD, or even eighty times more pixels than a DVD. But is not it getting enough?

A lot of ink has already flowed over viewing distances and visibility of certain resolutions. Because you can perceive more detail when you are closer to something, the visual acuity of the human eye is expressed in line pairs or cycles / degree. That indicates how many white-black line pairs you can see within a field of view of a degree. A line pair then corresponds to two pixels.

If you assume someone with 20/20 vision, this means that we can distinguish approximately 60 pixels / degree (30 cycles / degree). It is no coincidence that this is also the definition used for Apple Retina screens. After some calculations we can state that with 20/20 visibility and Ultra HD 4K resolution (so no 8K!), The screen may already approach 0.8x the image diagonal for your individual pixels.

[19659006] But that 20/20 guideline is an arbitrary limit, we also call it Snellen Acuity to the Snellen ophthalmologist test. However, further research shows that in the center of our eye we can observe up to 150 pixels / degree or more ( here and here for those who want research), that is the so-called ‘ simple acuity ‘, based on the number of photoreceptors in the eye. And in other tasks, where our brain assists visual perception, our view is even sharper, for example when we have to determine whether two lines are aligned (Vernier acuity) or points are aligned, whether lines are straight or not, and so on. We generally call this ‘Hyperacuity’ (hyper visual acuity, here for more info). An important reason to take this into account is the fact that image artefacts (of compression, noise, moiré, deinterlacing, etc.) can be perceived much more clearly, just because we know that the image is ‘not right’. If we judge whether an image feels ‘real’, we have to take into account a higher sharpness view. The SMPTE is therefore based on a sharpness of 120 pixels per degree.

If we use that to calculate where you can approach an Ultra HD 4K screen, we arrive at 1.6 times the screen diagonal. For a 65 “screen, for example, that is 2.5 meters. Since the viewing distance in a living room is on average somewhere between two and three meters, 4K is more than enough.

If we calculate the viewing distance for an 8K screen, you end up at 0.8 times the screen diagonal. Anyone who even takes into account 20/20 sharpness of view is 0.4 times the screen diagonal. For a 65 “screen you have to sit somewhere between 1.3 meters and 0.65 meters in front of the screen to see all the detail. That seems to have little or no use in the living room.

How do we use 8K then?

Is there no scenario in which 8K makes sense? Yes, but you have to get away from a typical living room scenario and think more of real immersion in the image. The human field of vision is about 170 °, we see almost everything that is in front of us, but the central 90 ° angle of our field of view are the things that we really see, experience and remember.

If we assume that we are In a typical living room, with a viewing distance of about 2.7 meters, a 55 “screen offers a field of view of approximately 25 ° and a 65” screen a field of view of 30 °.

That is far too little to really experience the image, a fact that cinema lovers know all too well. SMPTE recommends a minimum viewing angle of 30 ° for the cinema, and a maximum of approximately 60 °. This amounts to a viewing distance of approximately 1.6 times the screen diagonal for 30 ° and 0.8 times the screen diagonal for 60 °. For example, for projectors we have had a viewing distance of about 1.5 times the screen width for years, which amounts to a field of view of approximately 37 °.

If we translate this to house-room sizes (viewing distance of 2.7 meters), then so you have at least a 65 “screen in your home (for 30 ° field of view), but in order to get 60 ° field of view you need a 140-inch screen. For the sake of clarity, a 140 “screen (16: 9) has a width of 3.1 meters and a height of 1.75 meters.

The latter is already larger than what would be possible in many living rooms. If we want to go even further, and fill in 90 ° field of view, you can not be more than 0.4 times the screen diagonal. That is a 240 inch display at the typical viewing distance of 2.7 meters. That is 5.3 meters wide and three meters high! It is clear that such ‘experience’ will not come to the living room quickly.

Ultra HD 8k therefore seems more of a ‘business’ application to us. That will be fantastic in a museum. Or in other gigantic image arrangements, for example the lobby of the Cosmopolitan hotel in Las Vegas.

Content

A television with Ultra HD 8K resolution, it looks impressive, but actually do you need corresponding 8K content, and that may take some time. Take a look at the UHD roadmap at the beginning of this article. The implementation of that, especially when we talk about television broadcasts, is not finished yet. Ultra HD 4K content is still a very rare sight in television broadcasts for the time being. Those who watch via satellite can watch a few channels (mainly with demo material), but via cable, or IPTV, there is no mention of UHD 4K content. It may be there this year, although it remains to be expected (the World Cup 2018 and the Winter Games 2018 will be recorded in Ultra HD 4K HDR, but whether we will view them depends on local providers)

The hesitation of providers is undoubtedly partly due to the extra bandwidth required by an Ultra HD 4K signal. Bandwidth is expensive, and providers prefer to stop more channels in their limited bandwidth, rather than filling them with some Ultra HD channels. An Ultra HD 4K signal easily requires around 35-40 Mbit / s (in HEVC), and a UHD 8K signal increases that to 50 Mbit / s (in HEVC and even to 91 Mbit / s in H.264) (see here ). If you then know that a typical Full HD signal fits within 4-12 Mbit / s, then you understand that hesitation. In addition, providers have to invest significantly internally in equipment that can work with 4K. And providers that work with set-top boxes for digital TV also need to provide new hardware for the consumer, and they will probably want to postpone that until there is a decent offer. Considering all those hurdles that 4K still has to take, we think that 8K content will really take a lot of years.

The cards are better for streaming services (Netflix, YouTube, Amazon, etc.). They all have Ultra HD 4K content on offer, and their catalog is growing steadily. Switching to Ultra HD 8K is not that difficult for them, although the need for a larger bandwidth is an obstacle. This is also the case for the consumer. A YouTube UHD 4K stream requires 20-50 Mbit / s, for an Ultra HD 8K stream you can quickly double that. This can become a problem on many internet connections (even though we are well-equipped in Belgium and the Netherlands).

Anyone who hopes that physical media will be the solution, should be completely disappointed. Ultra HD Blu-ray is not provided on 8K content. So another format would be needed for this. Physical media are also doing less well worldwide. So if we ever even see an Ultra HD 8K disc is doubtful.

Scaling is the future

It seems more and more that upscaling will play an important role in the future. That is already the case because the majority of our content is 1080p, 720p or even lower (for example, DVD and we watch that on Full HD or Ultra HD screens.) But when you have an Ultra HD 8K screen in your home, then even Full HD content can be enlarged 16 times!

TV manufacturers are therefore becoming increasingly clearer on the processing performance of their devices, such as the Panasonic HCX², Philips P5 and the more recent Sony X1 Ultimate, LG alpha9 and Samsung’s AI solution .

Schematic overview of the new Samsung upscaling techniques

New techniques based on artificial intelligence and machine learning come prominently Conventional scaling techniques often lead to somewhat soft images, because high-frequency information (read: detail) was obviously not present in the original low-resolution image A recent academic publication by researchers at the Max Planck Instituut discusses a technique in which one attempts to synthesize textures with natural detail, rather than staying as close as possible to the original on a pixel basis. This sometimes leads to impressive results, which are often very close to the original visually. The technique is not yet completely flawless, but it does show the future direction. If you want to read the full paper, you will find it here . An illustration from the paper clearly shows the impact of this solution.

8K Ultra HD

On the right the original (ground truth), and then from left to right: a basic example of bicubic upscaling, a version of the proposed algorithm without texture synthesis (ENet-E), and a version with texture synthesis (ENet-PAT).

Conclusion

Ultra HD 8K looks sensational, but has only a very limited (to none) ) added value in the living room. With screen sizes of 55 to 65-inch, 4K will suffice. In applications where you really want to be close to the image, and we aim for a real realistic experience, on being present, then 8K is necessary.

We also link that to how difficult it will be to get real 8K collecting content, the utility of 8K becomes even more limited. We do see a development in scaling techniques that replace the need for 8K content. Upscaling is likely to be the main source of 8K content for some time.

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