“Ultra HD,” of course, means much more than just higher spatial
resolution (4K and 8K), even though that is to what many in the industry
and consumers equate it. It includes four other image as well as
immersive audio technologies. The four other image technologies are high
dynamic range (HDR), wide color gamut (WCG), deeper sample bit depth
(higher number of coefficient bits for the digital samples), and high
frame rate (HFR). All of these technologies combined create a much more
realistic and immersive TV viewing experience than today’s conventional
HDTV, without requiring any special head gear (such as that required for
the near-totally immersive virtual reality techniques that are also a
new exciting area of discussion).
BANDWIDTH CONSTRAINTS
As is typical, pre-produced content is ahead of live TV broadcasting
for delivering UHD, with Ultra HD Blu-ray discs and some on-demand or
over-the-top services already providing both 4K and HDR. This should not
be a surprise: it’s much easier to implement new services when one
controls both ends of the ecosystem, with only a passive delivery pipe
in between. All post-production is done in advance, with the
receiver/player/rendering/etc. acting on the content, unchanged by the
delivery mechanism, whether via wire, wireless or “sneaker net.” With
live TV broadcasting, there is no advanced post-production; all is done
in real-time. Live changes (such as logo insertion, lower thirds,
graphic overlays, picture-in-graphics, squeeze & tease, cross-fades
for interstitials, or country-specific format conversions, etc.) could
occur at each “node” along the live broadcast chain. Another major
factor is available bandwidth; there simply may not be sufficient
bandwidth to delivery UHD services, especially for the technologies that
require a lot more bandwidth than today’s conventional HD services do.
Lastly, there may be regulatory restrictions impacting new services over
certain networks, such as over-the-air broadcasting, that prevent
economically-viable transmission of UHD services.
As previously mentioned, all of the five image technologies combine
to give a much more compelling visual user experience than today’s
conventional HDTV, so if a content/service provider is able to offer a
UHD service that includes all five, then fantastic. Definitely offer
this compelling, much more realistic TV viewing experience. Consumers
will be thrilled.
However, what if bandwidth constraints prevent the content/service
provider from offering “full UHD,” so to speak? Should the provider just
resign itself to continue with today’s conventional HD service?
Absolutely not. The combination of HDR + WCG + 10-bit sample depth
(which many of us refer to as “HDR+”) has been shown in numerous
demonstrations to have fantastic “wow” factor for consumers. And the
good news is, depending upon the HDR+ scheme chosen, the bandwidth
increase over conventional TV (what’s now referred to as standard
dynamic range + narrow color gamut + 8-bit depth) is minimal, in the
general range of zero-20 percent when using the new HEVC video
compression at direct-to-consumer bitrates… most definitely the Best Bang for the Bit.
Compare this to 4K resolution: Even with the best video compression
available today (HEVC), 4K resolution still requires somewhere around
250 percent the bandwidth of conventional HD (also coded using HEVC, for
apples-apples comparison). And since the “bread and butter” of revenue
still will be the conventional HD service, this bandwidth requirement
most likely will be in addition to the existing service (that is,
simulcast will be required).
IS 4K NEEDED? WHY NOT 1080P?
So in the case of bandwidth constraints, why not transmit in 1080p
HDR+ and achieve the “wow” factor of HDR+? All 4K TVs upconvert 1080p to
2160p (4K) and the newer UHDTVs (4K + HDR+) will display an HDR+ image
if the incoming stream has HDR+ coded, regardless of the spatial
resolution. Many consumers may not even realize that the image was
upconverted to 4K: An oft under-discussed issue is that the proper
viewing distance for the human visual system to resolve 4K resolution is
approximately 1.5x the picture height of a 16:9 display, whereas HD
resolution can be resolved in full as far back as 3x the picture height.
In most TV viewing environments today, consumers are sitting back from
the display about 2.5-3.5x the picture height, therefore not really
“seeing” much difference between HD and 4K.
Ericsson has done “unscientific” experiments at trade shows over the
past two years, with two equal size flat screens side-by-side and we
asked attendees which image they preferred (without telling them what
they were looking at). Almost 100 percent would select the 1080p HDR
display over the 2160p SDR display (and this was done at the proper
viewing distance). This unscientific experiment is just one of many that
have shown the “wow” factor of HDR+ to consumers, regardless of screen
resolution.
So what about HFR? Like 4K resolution, HFR requires lots of changes
in the studio and post production facilities. Its impact is also related
to how fast or complex the scene motion is, so it’s extremely useful
for high motion sports and nature documentaries, but doesn’t do anything
much at all for “talking heads” and other low motion content. While
there are examples of specialty content being shot at HFR—for video,
this is defined as anything higher than 50 or 60 fps (country
TV-standard specific), but it typically refers to 100 or 120 fps
today—wider use of HFR likely will not occur for several more years to
come, so it is not so big an issue for today.
In summary, if a provider is able to offer a UHD service that
contains all of the five image technologies than definitely do it. This
is just so much better than today’s conventional HD. However, if
bandwidth constraints prevent “full UHD” from being delivered, the Best Bang for the Bit is definitely 1080p HDR+… with much of the “wow” factor and a far superior user experience over today’s conventional HD.
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