(^30) [ April May 2019 [soundandvision.com
low ends to map content directly,
meaning that it should be able to
reproduce the same peak bright-
ness and black level the content
was mastered at. Unfortunately,
that isn’t always the case, and
the display needs to determine
how to handle content that
goes beyond its capabilities
using a process called “tone
mapping.” With tone mapping,
any extra brightness gets, to put
it bluntly, crammed into a smaller
amount of space at the upper
limit of the display’s range. The
same thing also happens at the
low end as near-black tones
get mapped to the display’s
measured black point. While
the Dolby Vision system has its
own tone mapping standards,
HDR10 does not, so each display
manufacturer is le to their own
devices to handle HDR10 tone
mapping—something they do
with varying degrees of success.
Ideally, a display would handle
tone mapping consistently for all
content, but that’s not the case
yet. What we are starting to see is
solutions that help to mitigate the
problem, such as the built-in tone
mapping feature of the Pana-
sonic DP-UB820 Ultra HD Blu-ray
player that I reviewed in Sound
& Vision’s October/November
2018 issue.
BT.2020 VS. P3 COLOR
Another confusing issue with
HDR is the BT.2020 color space
that it’s associated with. No
current consumer video displays
can provide full coverage of
BT.2020, a color space that was
designed to allow headroom for
future technology developments.
Movies are largely mastered in
the P3 format, which is wider
than the REC. 709 one used
for HDTV, but not as wide as
BT.2020. However, P3 is not a
consumer format, and it’s incom-
patible with the color matrix
used for consumer video. So,
while it’s common to see color in
HDR content referred to as P3,
the reality is that all HDR content
is mastered using the BT.2020
color profile, which contains its
own P3 color coordinates. (If you
HDMI version 2.0a connections
to pass Ultra HD video with static
HDR10 metadata. Be careful
when selecting HDMI cables
though, since not all provide the
18Gbps bandwidth needed to
pass full 4K/60p signals. Look
for cables that carry a certifica-
tion symbol to ensure sufficient
bandwidth for your required
cable length. You’d be surprised
how many cables (including
ultra-expensive ones) don’t
provide the bandwidth needed
to pass signals properly.
THE FUTURE IS NOW
Many sources—Ultra HD Blu-ray,
Amazon Video, iTunes, Vudu,
YouTube, satellite, and more—
now support HDR, and the
range of compatible hardware
and content will only continue
to grow. It’s an exciting time for
video as more displays hit the
market with performance levels
we’ve only dreamed about, and
also at incredible prices given
the advanced technology that’s
onboard. If you haven’t yet expe-
rienced HDR, I highly recom-
mend doing so to see what the
future of video is all about.
similar to what’s seen in more
traditional video playback
systems. It permits greater
flexibility to accommodate a
range of production environ-
ments and display capabilities,
which is why HLG is being
employed by TV broadcasters.
DirectTV and Dish are also using
HLG to provide HDR for certain
sports events being transmied in
Ultra HD format.
HDR10+ is a format introduced
by Samsung that, similar to Dolby
Vision, delivers frame-by-frame
metadata and should provide
benefits with the company’s TVs
that use dynamic processing to
increase contrast performance.
So far, HDR10+ has appeared on
a handful of Blu-rays and has also
been implemented by Amazon for
portions of its streaming content.
HDMI AND HDR
The final thing to consider with
HDR is our old friend (or enemy),
HDMI. You’ll need gear with
were to calibrate a consumer
display directly for P3 and then
use it to display HDR content,
there would be significant color
issues since the color coordi-
nates are completely different.)
While HDR always uses BT.2020
color, the content can range
from black-and-white to images
with saturation levels that barely
exceed REC. 709, P3, or any color
space within the gamut envelope
of BT.2020. To put it another way,
just because a car can do 200
mph (BT.2020) doesn’t mean it
will go that fast; we are limited to
65 mph (P3) because that is what
the road infrastructure currently
supports.
HDR FLAVORS
Now that I’ve summarized what
HDR is, let’s discuss the various
formats mentioned above in
more detail. HDR10 uses static
metadata to communicate infor-
mation about the content being
fed to the display. This includes
the specs of the display monitor
originally used to master the
content (black level, peak bright-
ness level, and color gamut) as
well as the content itself (the
highest value for any single red,
green or blue sub-pixel, along
with average pixel level). While
this data does provide a snap-
shot of the content, it only repre-
sents the extremes. Dolby Vision,
in contrast, supplies per-frame
metadata. This helps enormously
with flat-panel TVs since informa-
tion is available for each video
frame to guide the display’s
dynamic contrast processing.
(The same information would go
far to improve performance with
lower light-output systems like
projectors, which require much
more aggressive tone mapping
than flat-panel TVs require,
but consumer 4K projectors
are currently limited to HDR10
support.) Dolby Vision also uses
color metadata that provides
12-bit precision to eliminate color
banding, although this typically
gets processed at 10 bits since
most displays are not 12-bit-
capable.
HLG uses a variation of gamma
HDR EXPLAINED
Above: BT.2020 (UHDTV/
HDR) vs. Rec. 709 (HD/SDR)
color gamut.
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