While the rest of the world is wondering about when we will see 4K broadcasts, NHK in Japan is conducting test transmissions of 8K Super Hi-Vision signals over the air. Its latest test demonstrated a signal with 16 times the resolution of high-definition sent over a single terrestrial television channel.
The standards for Ultra-High-Definition or UHDTV include both 8K and 4K profiles. An 8K Super Hi-Vision image has a resolution of 7680×4320 pixels, or over 33 megapixels, which is four times the resolution of a 4K or 3840×2160 image, or 16 times the resolution of a full-frame high-definition picture.
In its latest test, at the research laboratories of NHK in Hitoyoshi in southern Japan, an 8K signal was transmitted over a standard 6MHz broadcast channel and received 27 kilometres away.
New technologies were used to increase the transmission capacity, including combined horizontal and vertical polarization of the signal.
NHK claimed the first successful terrestrial transmission of a Super Hi-Vision signal in May 2012. That used two terrestrial television channels and was received over a distance of 4 kilometres.
NHK will use SHV at the Sochi Olympics in Russia and show it on public screens in Japan.
The NAB Show in Las Vegas in April is likely to see the first over-the-air transmission of Super Hi-Vision outside Japan.
Satellite test broadcasts in Super Hi-Vision are planned for the Olympics at Rio de Janeiro in 2016, in preparation for full broadcasts of the Olympics in Tokyo in 2020.
So while manufacturers are already pushing 4K televisions as the next big thing, we can probably look forward to 8K in the not too distant future.
Meanwhile, a more pressing practical problem may be frame rate. There are demonstrable benefits to higher temporal sampling, which may be even more important than increased spatial resolution.
The ITU standard for UHDTV, generally known as Recommendation 2020, specifies a range of frame rates including 60 and 120 frames per second. Some researchers have proposed that even higher frame rates may be desirable.
Some have suggested the need for frame rates divisible by 50 to avoid possible interference from mains lighting and facilitate down conversion in regions where the electricity frequency is 50 cycles per second. Others have suggested that it should be dynamic, depending on the subject matter.
The real problem is that the market may become flooded with large flat screens that natively only support lower frame rates, even if they allow higher presentation rates through interpolation. The HDMI 1.4 connector standard only supports 4K at 30 frames per second, while the latest 2.0 version only goes up to 60 frames per second.
Early adopters of 4K run the risk of premature standardisation, just as 720p and 1080i sold consumers short on what high-definition could deliver, because 1080p was not ready at the time.
Although 8K may be the longer-term objective, frame rate may be as much an issue as resolution, both for production and distribution.