HAVING seen interest in 3D television fizzle, consumer-electronics firms are desperate to find some other blockbuster product that will get customers back into big-box stores. The development most are hoping will do the trick is a display technology known as Ultra High-Definition that offers four times the resolution of today’s 1,080p HDTV sets.



At the recent Consumer Electronics Show in Las Vegas, talk of Ultra HD was on everyone’s lips. A handful of Ultra HD sets were even on display. No question, Ultra HD provides stunning images—at least when displaying content created in the new “4K” video format. Unfortunately, 4K content is virtually non-existent.



So far, only a handful of feature films have been shot with cameras capable of 4K, including “The Amazing Spider-Man”, “Prometheus” and “The Girl With the Dragon Tattoo”. That is hardly surprising given the amount of work involved. Insiders reckon making a full-length digital feature in 4K is equivalent to producing six ordinary 2K films.



Even so, some 17,000 cinemas around the world now have digital projectors capable of showing 4K films. So, if and when Hollywood upgrades wholesale to the new video standard, cinema-goers will be able to decide whether 4K is worth the premium they are bound to be charged.



The recent flood of 3D films largely failed that test. The lacklustre sales of 3D television sets suggest they are now doing the same. Will 4K suffer the same fate? It is far too early to say. But, for sure, 4K television—far more than 4K cinema—faces some formidable challenges.

As with 3D, the new television format takes its lead from Hollywood's initiative to produce sharper, more realistic images, even if that means upsetting cinema traditionalists. The existing wide-screen digital format used in film-making has 1,998 pixels across the frame and 1,080 down it. The new 4K standard has twice that resolution both vertically and horizontally—ie, 3,996 pixels across the frame and 2,160 down—making it four times sharper overall.



By contrast, the 4K television format is slightly narrower, having 3,840 pixels across and 2,160 pixels down. The screen width was reduced to maintain the 16:9 aspect ratio of HDTV, with its 1,920 by 1,080 pixel count. Doing so makes it easier to show existing video content that has been "up-scaled" for Ultra HD without having black “letterbox” bands above and below the picture.



It should be noted here that the sharpness of a television set has long been defined in terms of screen height—that is to say, by the number of visible scan lines, or rows of pixels, from the top of the screen to the bottom (eg, 480, 720 or 1,080 lines). With 4K television, however, the resolution is specified in terms of the screen width—with K representing the number (in thousands) of pixels across the screen.



Which measure will prevail will depend on how Ultra HD is marketed. Calling it merely 2,160p could make Ultra HD seem only twice as good as HDTV's 1,080p, while 4K suggests it really is four times better. The betting is that television makers will follow the film industry and label their new sets 4K.



But who actually needs a super-sharp 4K television? The resolution of even an HDTV set with 1,080 progressively scanned lines (ie, continuously from top to bottom) is wasted on the vast majority of viewers. Most sit too far from the screen to be able to see the actual detail it offers.



A study done some years ago by the now-defunct RCA Laboratories in New Jersey found the median eye-to-screen distance in American homes to be nine feet (2.7 metres). But because of the human eye's limited acuity, people even with 20/20 vision should, as a rule, sit no further than 1.8 times the width of the screen away from it if they are to distinguish the detail displayed (see “Devil in the details”, August 19th 2011). At a distance of nine feet, an HDTV set would need to have a screen of around 70 inches across a diagonal for viewers to benefit from the resolution they have paid for. With anything smaller, details simply blur into one another at that distance. A 40-inch HDTV set—the most popular size today—needs to be watched from five feet or closer. No question that, with twice the resolution horizontally and vertically, a 70-inch Ultra HD set would be pretty impressive even from nine feet away, and would still provide resolvable detail at twice that distance.



Then there is the issue of size. Today’s HDTV sets begin to look spotty when their meagre 2.1m pixels are spread over screen sizes greater than around 80 inches. With 8.3m pixels to play with, Ultra HD screens can be made twice as large without the gaps between the pixels becoming too obvious. In short, Ultra HD would seem more appropriate for home theatres than living rooms.



The biggest hurdle, though, will be getting native 4K content onto an Ultra HD screen. In raw form, a two-and-half-hour film shot in 4K at the usual 24 frames per second would contain some 216,000 frames. With each frame of the film containing 8.6m pixels, and each pixel having 24 bits of colour information, the resulting video file would comprise a whopping 5.6 terabytes of data.



Even with compression, transmitting such humongous files over the air or by cable would require more bandwidth, at far greater infrastructural cost, than broadcasters can afford. Streaming a feature-length 4K file over the internet would run into similar bandwidth constraints. The internet connection needed would have to transport data at speeds up to a gigabit a second. Few have broadband connections that fast at home.



An alternative would be to distribute 4K films as Blu-ray discs, just as 2K films are sold—or were until people switched to streaming them instead from Netflix, YouTube, iTunes and other online services. A 2K film etched on a Blu-ray disc uses all 50 gigabytes of its two recording layers. A 4K film would require a third, or even fourth, layer. Even then, a more efficient compression method than the current H.264 would be needed to shoehorn a 4K film into a Blu-ray disc.



The question is how “lossy” could a compression method afford to be before it compromised the quality of a 4K picture. The international bodies responsible for compression standards have been discussing a successor to H.264 for the best part of a decade. The latest draft, known as High Efficiency Video Coding, is said to double H.264’s compression ratio without loss of image quality.



Even if it proves up to the job, it will take years for the new compression standard (H.265) to be adopted universally. Many in the industry feel that, if 4K television is to succeed, an entirely new way of encoding and delivering its content is going to be needed.



Sony’s answer is to bundle a media server with its first generation of Ultra HD television sets. The server will come with ten films preloaded on its hard-drive, along with a selection of short videos. Sony says the films included will be copies made directly from pristine 4K masters. But no-one has said how customers will add new titles to their servers.



Perhaps they never will. Such a kludge is little more than a stop-gap measure, designed to encourage wealthy early-adopters to splurge on the latest video fad. (Sony’s 84-inch Ultra HD set costs $25,000.) If Ultra HD is to be HDTV's successor, then sooner or later cable and satellite TV providers, as well as streaming video services, will have to find ways of delivering 4K content reliably and cheaply. Your correspondent has no doubts they eventually will. But he has no idea how or when.



As for timing, the only guide is the penetration of HDTV over the past decade. The first nationwide broadcast in digital high-definition was John Glenn’s liftoff in the space shuttle Discovery in 1998. It took another dozen years before HDTV went mainstream. By that reckoning, it could be 2025 before Ultra HD is likewise in half of American homes.