Barry Fox’s technology column
The Fox Report
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Dolby a royalty to use DolbyVision.
Hardly surprisingly, the BBC uses
only HLG, which needs no such
metadata and is royalty free.
Andrew Cotton then explained the
practical challenges of using any HDR
system: ‘The challenge for HDR is live
sports, where there can be 40 cameras,
most of them different – including
stump cams inside cricket stumps –
and a mix of SDR (standard dynamic
range) and WCG/HDR is inevitable.
For the Royal Wedding we were using
76 cameras. I had to go out to a local
shop and buy a memory card so that
we could download and install some
new software updates.
‘For the foreseeable future mixing
SDR and WCG/HDR camera signals
will be inevitable, and conversion
techniques developed by the movie
industry do not work well for TV.
Fortunately, most UHD HDR cameras
also output an HD signal. And the BBC
has developed ‘scene light conversion’
software to match HLG HDR and SDR
signals. Details to follow....’
‘There is still work to be done,
though, especially on matching
colour, even when cameras output
both BT.709 colour for SDR, and
BT.200 for HLG HDR. We thoughtT
he International Moving
Image Society’s (IMIS) 88th
Annual Awards Ceremony
and lecture held recently in memory
of Bernard Happé (once technical
manager of Technicolor and author
of seminal books on movie fi lm tech-
nology) featured two BBC top tech
gurus sharing the inside story of the
joint work done by the BBC and Sky
on shooting the 2018 British Royal
Wedding in 4K UHD HDR, and the
BBC’s work with 4K UHD on sporting
events including the 2018 FIFA World
Cup and Wimbledon Tennis.
Phil Layton (head of broadcast and
connected systems, BBC R&D) kicked
off with his views on the need – or
otherwise – for 4K resolution, with
8K coming soon.
‘Screen sizes of 50/55 inches are
needed to show the benefi ts of 4K
UHD, at the average UK viewing
distance of 2.6m’ he said. ‘This holds
good for screen sizes up to 100 or
110 inches. So 8K is only needed if
screens get larger than that or people
start moving closer’.
Andrew Cotton (principal
technologist, BBC R&D’s Broadcast
& Connected Systems Section) offered
some basic background on HDR (high
dynamic range) video, with WCG
(wide colour gamut).Signal sensitivity
The human eye’s sensitivity to light
is approximately logarithmic, with a
dynamic range of around 46 stops;
but the eye uses a moving range
window of around 14 stops. Modern
digital cameras capture 12-14 stops,
and when TV signals are distributed
with 8-bit code the dynamic range is
around 5-6 stops.
HDR seeks to bridge the gap between
human vision and digital capture and
display. The camera sensor uses an
OETF curve (opto-electrical transfer
function) and the display uses an
EOTF curve (electro-optical transfer
function). The OETF and EOTF curves
are not same, so an OOTF processor
(opto-optical transfer function) is
used to compensate.
The HLG (hybrid log-gamma) HDR
system developed by the BBC and
Japanese broadcaster NHK, adapts
to whatever the screen can handle.
Dolby’s rival proprietary system
DolbyVision relies on PQ (perceptual
quantisation) and continually
changing metadata to control the
display. Manufacturers must payThe future of TV
4K, WCG, 8K, OETF... Barry Fox disentangles the latest acronyms, gets a handle on the future of TV and
talks to the BBC tech gurus who explain that it is not just about pixel count.