Is the rec.2020 UHD color broadcast spec really practical?
May 22, 2014
Author: Jeff Yurek
I've often advocated on this blog for Pointer's Gamut as an important design goal for display makers but is it really practical today from a technology perspective? Pointer's Gamut covers a huge area and it's odd shape makes it awfully difficult to cover with just three primaries. Rec.2020, the leading Pointer's-covering color gamut broadcast standard and de facto standard for upcoming UHD broadcasts, demonstrates this perfectly. It uses very deep red and green primaries to ensure that all those purples and cyans can get squeezed it into the triangle.
rec.2020 needs a very saturated green and red primaries to cover 99.9% of Pointer's Gamut
It's certainly tough to make a display that can reproduce primary colors that are that saturated and it is especially hard to do so efficienctly. Until now the displays that have come closest rely on an esoteric and power-hungry laser backlight system that can only cover up to about 91% of rec.2020 spec. That is impressive given how ambitious rec.2020 is but a bulky $6,000 laser display doesn't exactly qualify as practical and it's certainly not a technology that we are likely to find in a tablet or smartphone anytime soon given it's low power efficiency.
That may be about to change.
My company, Nanosys, has been working on this problem and we now think it is practical to produce an LED LCD that covers over 97% of rec.2020 using Quantum Dot technology. The latest generation of our Quantum Dots emit light with a very narrow Full Width Half Max (FWHM) spec of below 30 nanometers for both red and green wavelengths. FWHM is pretty obscure spec to be sure but it means that the color is both very pure and accurate. That pin-point accuracy actually enabled us to demonstrate over 91% rec.2020 just by modifying an off-the-shelf, standard LCD TV set with a specially tuned sheet of Quantum Dot Enhancement Film (QDEF).
Nanosys demonstrates over 91% coverage of rec.2020 using Quantum Dots and a standard LCD TV color filter
Very impressive and even a bit better than the performance of that laser TV but still not quite all the way there. What else could be optimized to improve the system and get us closer?
Looking at the spectrum after the color filters revealed a significant amount of blue leaking through the green filter. This leakage was causing the blue point to shift away from the rec.2020 primary. By optimizing the system and selecting a different blue color filter material with a sharper cutoff, Nanosys engineers showed that it is possible to build a display that covers over 97% of the rec.2020 standard– with great power efficiency.
Quantum Dot enhanced displays are in mass production today, they are used in commonly available displays on the market today. Their high power efficiency also means they can be used in all kinds of devices from smartphones to TVs. So, for the first time, it is actually becoming practical to build displays that cover the massive rec.2020 standard and since rec.2020 is part of the UHD broadcast spec this great news for the next generation of 4K and 8K devices.