In Broadcast - March 2016 - 48


48

www.inbroadcast.com | Vol: 6 - Issue 3 | March 2016

InForm

High Dynamic Range Video
- Software Is The Solution
Mark Horchler, International Marketing Manager - EMEA examines how Elemental's
software is allowing organisations to embrace High Dynamic Range...

T

oday, there is much debate
about high dynamic range
(HDR) as a means to improve
video image quality in Ultra
HD. The challenge is evident in
colour space diagrams (see Fig.
1.) ITU Rec. 709 defined the high
definition (HD) colour space in
1990, and was limited by the
CRT display technology of the time,
including 8-bit colour.
ITU Rec. 2020, published in 2012,
defines a much wider colour gamut,
matching the capabilities of today's
flat screen displays. Delivering this
expanded gamut requires more bits
per colour to provide a richer, more
realistic viewing experience.
8-bit systems offer 256 levels per
colour, or 256×256×256 (=16,777,216)
different colours. In a 10-bit system,
there are 1024 levels per colour, or
over a billion different shades
Video images with large areas of
similar colour - a blue sky or a green
forest, for example - portrayed in an
8-bit colour environment can lead
to distinct stepping artefacts, where
the colour splits into visible bands
(see Fig. 2.) 10-bit colour makes
the difference between adjacent
shades much finer, reducing intrusive
banding.
More colours leads to a perceived

Standard dynamic range (left) versus high dynamic range (right)

improvement in image quality. This is
because there is a finer, more sharply
delineated difference between each
colour, even in subtle instances. To
the human eye, HDR more closely
approximates what is visible in the
natural world.
Screen Gamma
The emergence of the OLED screen
has raised the potential for HDR.
OLED is an emissive technology: the
pixel itself generates light. In the best
OLED screens, the black is remarkably
black, and high output devices that
can generate bright white levels are
available. Between the two extremes,
an OLED display is very linear - this
raises another benefit.
Historically, a gamma curve was used
to make the most of a CRT's available
dynamic range. It ensured the best use
of the available bandwidth, enabling
colourists to make artistic judgements

Fig.1 Rec. 2020 offers expanded colour space for HDR video

Fig 2. 8-bit colour (left) produces marked banding compared to 10-bit colour (right)

about how the limited range of colours
could be used.
The gamma curve has been replaced
by a new formula, the electro-optical
transfer function (EOTF), sometimes
called perceptual quality (PQ). EOTF
allows some existing distribution
architectures to carry HDR content,
and is incorporated into the highefficiency video coding (HEVC/H.265)
compression standard.
Compatibility
When colour TV was first introduced
it was backwards compatible: one
signal could be viewed on black and
white and on colour receivers, where
the black and white receiver ignored
the colour information.
Today, many industry players,
including Dolby, Technicolor, Philips
and BBC/NHK, advocate a backwardscompatible approach to HDR. Others,
especially those working in over-thetop (OTT) streaming and Blu-ray 2,
are less concerned with backwards
compatibility. Implementing their
proposals for broadcast could mean
swapping out encoders, decoders, and
set-top boxes.
In a dual-layer approach, Standard
Definition Range (SDR) and HDR video
streams are carried separately through
workflows, and the receiving device
selects which stream to accommodate.
This adds complexity, increases
required bandwidth, and raises
challenges for internal workflows,
especially
when
splicing
SDR
commercials into an HDR programme,
or inserting emergency broadcast
signal messages.
In a single-layer approach, the
architecture carries the SDR signal,

plus
additional
metadata
telling HDR-equipped devices
how to extend the dynamic
range. This provides full
backwards compatibility -
non-HDR devices will not
understand, and therefore
ignore additional metadata.
Introducing
additional
processing may limit the benefits of
extending the dynamic range.
Encoder designs need to ensure that
HDR can be achieved in real-time, as
live sport is a big HDR driver. It should
also not impose too much latency.
Software
Competing
proprietary
HDR
solutions are on the market, and
standards bodies are racing to keep
pace. Content owners could be asked
to deliver HDR content in different
formats for different distribution
platforms,
making
workflows
more cumbersome, and increasing
processing and storage costs.
Elemental
provides
softwaredefined
video
solutions
for
HDR
implementation,
allowing
broadcasters, service providers, and
content owners to create, manage, and
deliver HDR content.
Most importantly, this can be done
without forcing expensive decisions
and the outlay of substantial capital
for video infrastructure, and does not
require the maintenance of parallel
hardware HDR silos. Elemental
features a scalable, flexible approach
to future-proof video workflows kept
current through software updates.
This solution aligns with the
trend
towards
software-defined
architectures, and prepares companies
to take advantage of virtualisation and
the cloud.
It reduces both CAPEX and OPEX,
minimising risk for organisations as
they transition.
Elemental's flexible and scalable
software allows organisations to
embrace HDR quickly, lead the market,
and meet the expectations of their
audiences.
http://www.inbroadcast.com https://www.youtube.com/user/elementaltech
Table of Contents for the Digital Edition of In Broadcast - March 2016
