In Broadcast - August 2016 - 40

www.inbroadcast.com | Vol: 6 - Issue 8 | August 2016

InMedia

High Dynamic Range
Video - Software
Is The Solution

between approaches is the singleor dual-layer question. In a duallayer approach, standard dynamic
range (SDR) and HDR video streams
are carried separately through
the workflows, and the receiving
device selects which stream it can
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 system messages.
In a single layer approach, one
workflow carries the SDR signal, plus
additional metadata telling HDRequipped devices how to extend
the dynamic range. This provides
full backwards compatibility - nonHDR devices will not understand
and therefore ignore the additional
metadata. Introducing additional
processing may limit the benefits of
extending dynamic range.
Encoder designs also need to ensure
HDR can be achieved in real-time, as
live sport is a big driver for HDR. It
should not impose too much latency.

By Mark Horchler, Senior International Marketing
Manager EMEA at Elemental Technologies...

he Ultra High Definition (Ultra HD)
debate focuses on more pixels (4K
or 8K); more video images or higher
frame rates (HFR); and better video
image quality or high dynamic range
(HDR) and extended colour gamut.
HDR
can
increase
perceived
image quality, but how can it
be
implemented?
Technologies
exist to deliver HDR, although
standardisation remains unresolved.
Any implementation will require the
flexibility found with software-defined
video (SDV) solutions.
A technical and business case
consensus around HDR are needed.
Industry sub-sectors - such as pay TV
providers and the content producers
who serve them - will thrive or be
challenged, depending on the set of
specifications, standards and practices
that are ultimately adopted.
Every Bit Helps
The number of colours that can be
displayed in video is directly controlled
by bit depth. In an RGB system, the
bit depth of each colour determines
the total number of colours available.
An 8-bit system offers 256 levels per
colour. In a 10-bit system, there are
1024 levels per colour, or over a billion
different shades.
A billion colours may seem
unnecessary, but adding more subtlety
to shades enables smoother colour
transitions within colour families. In
a video image with large areas of a
similar colour, like a blue sky or green
forest - an 8-bit colour environment
can lead to distinct stepping artefacts
where the colour splits into visible
bands. 10-bit colour makes the
difference between adjacent shades
much finer, reducing visible and
intrusive banding.
More colours leads to a perceived
improvement in picture sharpness:

HDR can make a video
image look like it has more
pixels due to the finer, more
sharply delineated difference
between each colour. To
the human eye, HDR more
closely approximates what is
visible in the natural world.
Finally, HDR can extend the
dynamic range by making
the blacks blacker and the
whites whiter while retaining
smooth,
linear
colour
transition in the mid-tones.
Display Technology
CRTs are limited in terms
of light level ranges they
can generate. Attempts to
improve brightness from
a CRT results in increasingly smeary
pictures, which reduces rather than
increases the perceived resolution.
Liquid crystal displays (LCDs) are
also limited in dynamic range. Even
when a pixel is notionally set to black,
some light leaks through, and when set
to white, it is not perfectly transparent.
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 are being
made that can generate bright white
levels. Between the two extremes,
OLED
screens
are
remarkably
consistent.
This linearity raises another benefit.
Historically, a gamma curve was used
to make the most of the available
dynamic range of the CRT. It ensured
best use of available bandwidth,
enabling colourists to make artistic
judgements about how the limited
range of colours could best be used.
The gamma curve has been replaced
by a new formula, the electro-optical

transfer function (EOTF), sometimes
called perceptual quality (PQ). This
provides a more granular way of
mapping luminance while retaining
creative control. EOTF allows some
existing distribution architectures to
carry HDR content, and is incorporated
into the high-efficiency video coding
(HEVC/H.265) compression standard.
Compatibility
When colour TV was introduced
it was backwards compatible: one
signal could be viewed on black and
white and colour receivers, where the
black and white receiver ignored the
colour information. Today, companies
including Dolby, Technicolor, Philips
and BBC/NHK, advocate a backwardscompatible approach to HDR.
Others, especially those working
in 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.
Another
structural
difference

Software
There is a genuine interest in HDR as
a means of delivering more engaging
content to consumers. HDR can deliver
a real boost to perceived video quality
at a modest additional budget per bit.
The practicalities, however, are far
from finalised. Competing proprietary
solutions are on the market, with
standards bodies 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 content. This solution aligns
with the trend towards softwaredefined architectures, and a readiness
to take advantage of virtualisation
and the cloud. It reduces both capex
and opex, minimising risk during the
transition. Elemental's flexible and
scalable software allows organisations
to embrace HDR quickly, and meet the
expectations of their audiences.

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Table of Contents for the Digital Edition of In Broadcast - August 2016