So Where Did the Idea of 8K Come From?
At IFA in 2022, the author was asked by a big consumer electronics company to give briefings to journalists on the topic of 8K. He was surprised that almost none of them knew where the idea of 8K came from. Most just assumed that 8K was a simple extension of 2K (FullHD) and 4K (UltraHD) to another level to reflect improving technology.
However, that is not how the idea came about. More than a decade ago, there was a decision to work on a next generation of video technology that would come to readiness in time for the Tokyo Olympics in 2020. The aim was to make this a showcase for the best possible audio and video technology in terms of colours, dynamic range (contrast) and other features of picture quality. The question was “How to make the most immersive, engaging and realistic images?”. One of the areas that was looked at was spatial resolution.
Boosting spatial resolution was seen as important because it was correctly anticipated that viewers would be using bigger and bigger screens as the world was moving to flat panels, that did not have the same size constraints as traditional CRTs. Now, the ability of the eye to resolve detail depends on the size of the feature being observed and the viewing distance. Engineers wanted the best sense of immersion which comes from, among other things, a large image that covers a lot of the watcher’s field of view. Moving a display closer or making it bigger makes detail clearer, so you need more resolution to avoid the eyes seeing the dots that make up the image.
A major project was undertaken by a team led by Dr Kenichiro Masaoka a very distinguished (he was made a Fellow of the SID in 2021) display scientist of NHK, the Japanese broadcaster, to look at what resolution you really need to create full immersion. His project didn’t compare with existing technologies of the time, but with real objects. He asked viewers to compare images of an object with the actual object and try to decide if they could distinguish between the two. At low resolutions, everybody could. The research results showed(1) that many could easily tell the difference between the image and the object even as the resolution became quite high.
To get away from complex calculations that need to take into account the viewing distance of an object and its size, vision scientists tend to use the concept of ‘cycles per degree’ – that is to say, the number of black to white transitions that can be clearly seen in a single degree of vision. By focusing on the angle at the eye, the viewing distance is immaterial – you could be looking at big lines from a long way away, or thin lines close to.
It’s generally accepted that 20/20 vision (often used as a reference to ‘perfect’ vision, when actually it means ‘average’ vision) is around 30 cycles per degree. Young people with really good vision (and fighter pilots) have up to 20/10 vision (they can see what most people resolve at 10′ from 20′ away)(2). Dr Masaoka found that most people couldn’t distinguish between an image and reality at 60 cpd – twice the level that they would have scored in a vision test. He found some people that could readily identify the different items at over 150 cpd – and had the test gone further, he expected even higher results and in his paper he said that “an image resolution of several hundred cpd would be required for perfect visual realness”.
Turning to TV
If we take this idea of needing 60 cpd on the display, with an 85″ TV at a viewing distance of 2.7m, you need 120 pixels. To have 120 pixels in 1 degree, you have to have an 8K display and content if you want to get most people to have a sense that they are seeing reality.
The important point here is that the idea of 8K was not just a “what’s next?” thought, but came from a desire to most economically deliver a genuine sense of immersion with image quality that is closer to reality than can be obtained with FullHD and UltraHD. It’s nowhere near the only thing you need to do – HDR/dynamic range, colour and peak brightness are also very important – but without 8K, you can’t get to an image of reality.
The Wrong Comparison?
We often hear the comment at the 8K Association, that “there’s not as much difference between 4K and 8K as there was between 2K and 4K video”. There’s some truth to that, but the reality is that any video signal, even a 4K signal, seen from a consumer device and outside a studio will have been very compressed and much of the information, especially the small details and textures, will have been lost. However, newer codecs and camera technology are allowing more of that information to be captured and that will mean that signals and images should be able to get much nearer to reality.
In that case, isn’t the right comparison between 8K and reality rather than between 4K and 8K? We think so.
- Sensation of Realness From High-Resolution Images of Real Objects IEEE TRANSACTIONS ON BROADCASTING, VOL. 59, NO. 1, MARCH 2013 – Digital Object Identifier 10.1109/TBC.2012.2232491
- K. Masaoka, M. Emoto, M. Sugawara, and Y. Nojiri, “Contrast effect in evaluating the sense of presence for wide displays,” J. SID, vol. 14, no. 9, pp. 785–791, Sep. 2006.