Presentation heading or title
An Overview of the Hybrid
Log-Gamma HDR System
MediaNet Flanders and the Dutch Guild of
Multimedia Engineers
Andrew Cotton & Tim Borer
Date of Presentation: 31st January 2017
What to Expect
• Motivation for Hybrid Log-Gamma (HLG)
• Fundamentals of HDR
• Compare ITU-R PQ & HLG solutions
• HLG HDR in Production
• HLG HDR in Distribution
• HLG HDR in the Home
• Summary
An Overview of the Hybrid Log-Gamma HDR System
Motivation for developing HLG
An Overview of the Hybrid Log-Gamma HDR System
HLG Enables Easy Migration to HDR TV Production & Distribution
Jointly developed by BBC and NHK, included in ITU-R Recommendation BT.2100
• Specifically developed for Television
• Delivers high quality HDR pictures
•
Delivery to diverse displays
• In Production
•
•
•
•
Requires no metadata
Compatible with existing 10-bit infrastructure, codecs and equipment
Provides compatible picture on SDR screens
Migration only requires HDR cameras, and HDR displays in critical monitoring areas
• In Distribution
•
•
•
Supported by HEVC and HDMI 2.0b (via software upgrade)
Specified (alongside PQ) by DVB, ARIB and YouTube
Delivers a compatible image to SDR DVB UHD Phase-1 (BT.2020 colour) receivers & displays
An Overview of the Hybrid Log-Gamma HDR System
Metadata Free Operation Key to Unlocking Benefits
• Allows use of conventional circuits, routers, switchers and codecs
• Enables simple reliable and consistent production
• Delivers consistent results on consumer screens and devices
• Places no constraints on operational practices
•
Even simple metadata prevents, mixes, DVE and complicates graphics
An Overview of the Hybrid Log-Gamma HDR System
Metadata Free Operation Key to Unlocking Benefits
• Allows use of conventional circuits, routers, switchers and codecs
• Enables simple reliable and consistent production
• Delivers consistent results on consumer screens and devices
• Places no constraints on operational practices
•
Even simple metadata prevents, mixes, DVE and complicates graphics
• Same issues apply in consumer equipment
An Overview of the Hybrid Log-Gamma HDR System
Just like existing TV systems, HLG based on Relative Brightness
• Signal independent of the display
• Utilises entire code range regardless of mastering monitor
• Preserves the value of the archive as consumer displays get brighter
• Engineers and Craft staff read waveform monitors in the conventional way
• By design, entire image gets brighter as display brightness increases
• Allows HDR viewing in brighter environments whilst maintain the creative intent
• Allows consistent signals across a wide range of production environments and
displays
An Overview of the Hybrid Log-Gamma HDR System
HDR Fundamentals
An Overview of the Hybrid Log-Gamma HDR System
End-to-End Television Signal Chain
Scene Light
OETF
Video
Signal
Decoding
Encoding
Camera
Signal
OOTF
An Overview of the Hybrid Log-Gamma HDR System
EOTF
Display
Display
Light
Conventional SDR Camera Curve
Video Signal
1
0.8
0.6
0.4
0.2
0
0
0.5
1
1.5
2
2.5
Relative Sensor Output
An Overview of the Hybrid Log-Gamma HDR System
3
Camera Log Curve
Video Signal
1
0.8
0.6
0.4
0.2
0
0
0.5
1
1.5
2
2.5
Relative Sensor Output
An Overview of the Hybrid Log-Gamma HDR System
3
Best of Both
Video Signal
1
0.8
0.6
0.4
0.2
0
0
0.5
1
1.5
2
2.5
Relative Sensor Output
An Overview of the Hybrid Log-Gamma HDR System
3
HLG HDR Camera Curve
Video Signal
1
0.8
0.6
0.4
0.2
0
0
0.5
1
1.5
2
2.5
Relative Sensor Output
An Overview of the Hybrid Log-Gamma HDR System
3
Additional Dynamic Range in Blacks
0.2
0.18
Video Signal
0.16
HLG
0.14
0.12
BT.709
0.1
0.08
0.06
0.04
0.02
0
0
0.01
0.02
0.03
0.04
Relative Sensor Output
An Overview of the Hybrid Log-Gamma HDR System
0.05
HLG Camera Curve Similar to SDR Camera Curve With a “Knee”
Video Signal
1
0.8
0.6
0.4
0.2
0
0
0.5
1
1.5
2
2.5
Relative Sensor Output
An Overview of the Hybrid Log-Gamma HDR System
3
Banding
Image Quantisation
Original
An Overview of the Hybrid Log-Gamma HDR System
Extreme Banding
Quantization Effects (Banding):The Schreiber Threshold
0.1
0.09
Weber Fraction
0.08
0.07
De Vries-Rose Law
Critical Contrast  1/Y
Schreiber
0.06
0.05
Weber–Fechner Law
Critical Contrast  0.02Y
0.04
0.03
0.02
0.01
0
0.01
0.1
1
10
Display Luminance cd/m**2
An Overview of the Hybrid Log-Gamma HDR System
100
1000
10000
Quantization Effects (Banding): Gamma Curve
0.1
0.09
Weber Fraction
0.08
Schreiber
0.07
0.06
Gamma 8 bit
0.05
0.04
0.03
0.02
0.01
0
0.01
0.1
1
10
Display Luminance cd/m**2
An Overview of the Hybrid Log-Gamma HDR System
100
1000
10000
Quantization Effects (Banding): Gamma Curve
0.1
0.09
Schreiber
Weber Fraction
0.08
Gamma 8 bit
0.07
0.06
Gamma 10 bit
0.05
0.04
0.03
0.02
0.01
0
0.01
0.1
1
10
Display Luminance cd/m**2
An Overview of the Hybrid Log-Gamma HDR System
100
1000
10000
Quantization Effects (Banding): PQ
0.1
0.09
Schreiber
Weber Fraction
0.08
PQ
0.07
0.06
Gamma 10 bit
0.05
0.04
0.03
0.02
0.01
0
0.01
0.1
1
10
Display Luminance cd/m**2
An Overview of the Hybrid Log-Gamma HDR System
100
1000
10000
Quantization Effects (Banding): HLG
0.1
0.09
Schreiber
0.08
Weber Fraction
PQ
0.07
Gamma 10 bit
0.06
HLG 1000
0.05
0.04
0.03
0.02
0.01
0
0.01
0.1
1
10
Display Luminance cd/m**2
An Overview of the Hybrid Log-Gamma HDR System
100
1000
10000
Psychovisual Adaptation
Image plus surround
An Overview of the Hybrid Log-Gamma HDR System
Image in dark surround
“Rendering Intent” (Display Gamma)
Gamma too low
An Overview of the Hybrid Log-Gamma HDR System
Gamma correct
Gamma too high
Variation of Gamma for Perceptual Match
1.5
1.4
1.3
Gamma
1.2
1.1
Test 1
Test 2
ITU
1
0.9
0.8
0.7
0.6
100
1000
Peak image luminance in cd/m2
An Overview of the Hybrid Log-Gamma HDR System
Artistic (“Creative”) Intent
• Brighter environments need brighter pictures
• Different environments need different display gamma.
• Preserving luminance does NOT maintain creative intent
• The HLG signal, representing the camera output, remains constant.
•HLG displays adapt to preserve artistic intent (defined in BT2100).
• The PQ signal represents the image specifically for a reference display
•Dim environment
•Adaption for other brightness and environments not specified
An Overview of the Hybrid Log-Gamma HDR System
Compare ITU-R PQ & HLG solutions
An Overview of the Hybrid Log-Gamma HDR System
Just like conventional TV, HLG is “Scene-Referred”
PQ is “display-referred”
• Like the digital cinema standards, the signal
describes the absolute light output from
the mastering display
•
The signal is specified by the display EOTF
An Overview of the Hybrid Log-Gamma HDR System
•
Like BT.601, BT.709, Slog3, PanaLog etc., the HLG
signal describes the relative light in the scene
•
It is specified by the OETF (opto-electronic transfer
function), the camera characteristic
PQ Represents Absolute Brightness
e.g. 400 cd/m2 home theatre
e.g. Code Values 81 - 674
Display
Re-Mapping
e.g. Code Values 74 – 636
600 cd/m2 “shading”
e.g. OB truck
e.g. 1000 cd/m2 evening viewing
Display
Re-Mapping
e.g. Code Values 81 - 723
e.g. Code Values 81 - 728
e.g. 2000 cd/m2 daytime viewing
1000 cd/m2 “shading”
e.g. studio gallery
Display
Re-Mapping
e.g. Code Values 119 - 789
e.g. 4000 cd/m2 signage display
e.g. Code Values 74 - 789
•
2000 cd/m2 “grade” •
The signal varies with mastering display.
Display re-mapping often required.
An Overview of the Hybrid Log-Gamma HDR System
Display
Re-mapping
e.g. Code Values 158 - 940
HLG Represents Relative Brightness
e.g. 400 cd/m2 home theatre
Code Values 64 - 940
Code Values 64 – 940
600 cd/m2 “shading”
e.g. OB truck
e.g. 1000 cd/m2 evening viewing
Code Values 64 - 940
Code Values 64 - 940
e.g. 2000 cd/m2 daytime viewing
1000 cd/m2 “shading”
e.g. studio gallery
Code Values 64 - 940
e.g. 4000 cd/m2 signage display
Code Values 64 - 940
•
2000 cd/m2 “grade” •
The signal constant with mastering display.
Display adaptation inherent part of HLG EOTF
An Overview of the Hybrid Log-Gamma HDR System
Code Values 64 - 940
PQ and HLG work differently
• HLG
• Image brightness changes with display brightness
• Dynamic range of highlights constant
• Brighter displays for brighter environments
• PQ
• Image brightness constant with display brightness
• Dynamic range of highlights increases with display brightness
• Brighter displays for more highlights
An Overview of the Hybrid Log-Gamma HDR System
End-to-End Television Signal Chain
OETF: opto-electronic transfer function
EOTF: electro-optical transfer function
An Overview of the Hybrid Log-Gamma HDR System
Overall Transfer Function (OOTF) Non-Linear
Opto-Optical Transfer Function (OOTF)
• OOTF varies according to viewing environment and brightness of the display
• Traditionally a “gamma” law OOTF
An Overview of the Hybrid Log-Gamma HDR System
For “Scene Referred” Systems OOTF is Part of the Display
An Overview of the Hybrid Log-Gamma HDR System
For “Display Referred” PQ Systems OOTF is Part of the Camera
An Overview of the Hybrid Log-Gamma HDR System
End-to-End Both HDR Systems Identical in Production Environment
PQ signal chain
HLG signal chain
An Overview of the Hybrid Log-Gamma HDR System
BBC Believes PQ Display Rendering for Other Environments Requires Metadata for Optimal
Presentation
An Overview of the Hybrid Log-Gamma HDR System
Display Adjustments For HLG Needs No Metadata
An Overview of the Hybrid Log-Gamma HDR System
HLG HDR in Production
An Overview of the Hybrid Log-Gamma HDR System
HLG in TV Post-Production (other equipment available)
HLG “aware” grading software
• SAM Quantel Rio
• DaVinci Resolve
• SGO Mistika
• Filmlight Baselight
• Digital Vision Nucoda
• Colorfront
An Overview of the Hybrid Log-Gamma HDR System
HLG displays
• Sony BVM-X300
• Canon DP-V2410, DP-V3010, DP-V2420
• Dolby PRM-4200/4220 (internal 3D-LUT for HLG)
• SIM2 (external converter)
Landmark TV Productions already Produced in HLG
• BBC’s Planet Earth II
•
•
•
UHD HLG HDR
Baselight grade
Dolby PRM4220 (with internal HLG LUT) monitor
• Around 20 programmes for Sky Perfect Japan
An Overview of the Hybrid Log-Gamma HDR System
HDR Cameras
• Live HLG
•
•
•
•
Grass Valley LDX-86
Sony HDC-4300
Panasonic AK-UC3000
Ikegami UHK-430, SHK-810
• Non-live, “Raw”
•
•
•
•
•
•
Sony (using sLog3)
Canon
Arri
Red
Panasonic
Many others …………
An Overview of the Hybrid Log-Gamma HDR System
Setting the Signal Level
Camera
Zebra Stripes
An Overview of the Hybrid Log-Gamma HDR System
Production or Grading Suite
Waveform Monitor
Setting the Signal Level
• Diffuse white
• The brightness of ideal "matte" or diffusely reflecting surface
• Ill defined – varies with lighting
• Not all scenes have diffuse white
• About 90% signal level for conventional SDR TV
An Overview of the Hybrid Log-Gamma HDR System
“Diffuse White” in HLG
• Fixed signal level
•
referred to as “reference level for graphics”
• 75% signal level (75 “IRE”) proposed
• Good “compatible picture”
• Defines the number of stops for highlights
An Overview of the Hybrid Log-Gamma HDR System
“Diffuse White” in HLG
• Defined by the camera setup
•
e.g. 18% grey card or reflectance chart
• Varies with display brightness
•
•
•
•
400 cd/m2, 75 % =
1000 cd/m2, 75 % =
2000 cd/m2, 75 % =
4000 cd/m2, 75 % =
102 cd/m2
203 cd/m2
344 cd/m2
581 cd/m2
Levels for 1000 cd/m2
Reflectance
38%
26
90% Reflectance Card
73%
176
Graphics reference
75%
203
18% Grey Card
• About 2.5 stops allocated for highlights and speculars
•
Subject to artistic choice
An Overview of the Hybrid Log-Gamma HDR System
Nominal Reference
cd/m2
% HLG
Ensuring Consistent Brightness in PQ & HLG Production
• Operational Practice Guidelines define reference levels
•
•
reference levels provide an “anchor”
similar to audio line-up levels
• Objective brightness measure also needed
•
•
similar to audio loudness, e.g. EBU R128, ATSC A/85
in development
• Comfort level tests underway to establish acceptable brightness range
An Overview of the Hybrid Log-Gamma HDR System
Transcoding HLG to PQ
HLG Signal
HLG
Display EOTF
Display Light
Inverse PQ
Display EOTF
PQ Signal
PQ peak
mastering level
An Overview of the Hybrid Log-Gamma HDR System
Transcoding PQ to HLG
PQ Signal
PQ peak
mastering level
An Overview of the Hybrid Log-Gamma HDR System
PQ
Display EOTF
Display Light
Inverse HLG
Display EOTF
HLG Signal
However “Conversion” from PQ to HLG is Recommended
e.g. 400 cd/m2 home theatre
PQ Signal
Tone-Map to
1000 cd/m2
“Bridge”
PQ 1000
Signal
Transcode to
HLG
HLG Signal
e.g. 1000 cd/m2 evening viewing
PQ peak
mastering level
e.g. 2000 cd/m2 daytime viewing
•
Ensures consistent HLG signals
•
Avoids changes in brightness for different PQ peak mastering levels
e.g. 4000 cd/m2 signage display
An Overview of the Hybrid Log-Gamma HDR System
PQ <-> HLG Interconversion Easily Implemented
•
Already offered in grading software, distribution encoders and latest consumer silicon
An Overview of the Hybrid Log-Gamma HDR System
HLG HDR in Distribution
An Overview of the Hybrid Log-Gamma HDR System
Both HLG and PQ Will be Supported in CE Devices in Most World Markets
HLG and PQ Included in,
•
ARIB STD-B32, Video Coding, Audio Coding And Multiplexing Specifications for
Digital Broadcasting
•
DVB/ETSI TS 101 154 v2.3.1, Specification for the use of Video and Audio
Coding in Broadcasting Applications based on the MPEG-2 Transport Stream
•
Korea announced will support both HLG and PQ
•
YouTube HDR
https://support.google.com/youtube/answer/7126552
•
HDMI 2.0b (HLG software upgrade)
An Overview of the Hybrid Log-Gamma HDR System
Seven HLG TV Services Already “On-Air” Worldwide
• HLG Commercial Services
•
•
Sky Perfect Japan, launched October 2016
Travelxp 4K (Europe), launched January 2017
• Current HLG Test Services
•
SES Astra19.2°
• HLG Test stream
• NRJ (French Network) Test transmission
•
Eutelsat Hotbird 13.0°
• 4-Ever Project Test Channel
•
Tour Eiffel, Paris, France
• NRJ Test transmission
• NHK Super Hi-Vision
• BBC iPlayer
An Overview of the Hybrid Log-Gamma HDR System
HLG HDR in the Home
An Overview of the Hybrid Log-Gamma HDR System
Image Presentation
• HLG
• Brighter displays for brighter environments
• Image brightness changes with display brightness
• Dynamic range of highlights constant
• defined by diffuse white
• PQ
• Brighter displays for more highlights
• Image brightness constant with display brightness
• Dynamic range of highlights increases with display brightness
An Overview of the Hybrid Log-Gamma HDR System
Essential that HDR TV is suitable for HOME viewing environments
• BBC believes absolute brightness approach of PQ well suited to applications
where viewing environments the same and similar to the grading environment
(e.g. cinema, home movie theatre)
An Overview of the Hybrid Log-Gamma HDR System
Essential that HDR TV is suitable for HOME viewing environments
• BBC believes absolute brightness approach of PQ well suited to applications where
viewing environments the same and similar to the grading environment (e.g. cinema, home
movie theatre)
• But, viewers should not have to draw curtains during the daytime to watch HDR-TV
• Relative brightness approach of HLG, well suited to diverse home TV viewing
•
•
To preserve details in the blacks, presentation needs to be brighter than in grading suite
To preserver the impact of highlights, consumer screens may need to be brighter than grading
screens
An Overview of the Hybrid Log-Gamma HDR System
Relative Light Approach of HLG allows HDR viewing all day long
By design as HLG displays get brighter so does entire image, enabling HDR in brighter environments, e.g.,
Environment
Simulated images
• Home theatre projector
•
e.g. 400 cd/m2 peak
• graphics “ref” (75% HLG), 100 cd/m2
• Dim evening living room
•
e.g. 1000 cd/m2 peak
• graphics “ref” (75% HLG), 203 cd/m2
• Bright daytime living room
•
e.g. 2000 cd/m2 peak
• graphics “ref” (75% HLG), 344 cd/m2
An Overview of the Hybrid Log-Gamma HDR System
Stretching the blacks in HLG
0.1
0.09
Schreiber
Gamma 10 bit
HLG 1000
HLG 2000
HLG 3000
HLG 4000
HLG 10000
Weber Fraction
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0.01
0.1
1
10
Display Luminance cd/m**2
An Overview of the Hybrid Log-Gamma HDR System
100
1000
10000
HLG Appearing in Consumer Equipment
Product Announcements CES 2017
•
JVC
DLA-X5500, X7500, X9500 projectors
•
•
LG
W7, G7, E7, C7 and B7 OLED
•
• Updates for 2016 E6 and C6
•
Panasonic
EZ1000/EZ1002 OLED
Lumix GH5 DSLR
•
•
•
Sony
•
Sony Bravia A1/AE1 Series OLED
• Updates for 2016 models
•
Previously shown in TVs and projectors from
•
Panasonic, Samsung & Toshiba
An Overview of the Hybrid Log-Gamma HDR System
HLG Overview Summary
• HLG developed to allow straightforward migration to HDR Television
•
•
•
Supports a wide range of displays and environments
No need for metadata as OOTF is part of display EOTF
Can be displayed unprocessed on SDR screen
An Overview of the Hybrid Log-Gamma HDR System
HLG Overview Summary
• HLG developed to allow straightforward migration to HDR Television
Supports a wide range of displays and environments
No need for metadata as OOTF is part of display EOTF
Can be displayed unprocessed on SDR screen
•
•
•
• In TV Production HLG can use existing SDR infrastructure and monitoring displays
•
Only critical monitoring requires HDR displays
An Overview of the Hybrid Log-Gamma HDR System
HLG Overview Summary
• HLG developed to allow straightforward migration to HDR Television
Supports a wide range of displays and environments
No need for metadata as OOTF is part of display EOTF
Can be displayed unprocessed on SDR screen
•
•
•
• In TV Production HLG can use existing SDR infrastructure and monitoring displays
•
Only critical monitoring requires HDR displays
• Both HLG and PQ included in ITU-R Recommendation BT.2100
An Overview of the Hybrid Log-Gamma HDR System
HLG Overview Summary
• HLG developed to allow straightforward migration to HDR Television
Supports a wide range of displays and environments
No need for metadata as OOTF is part of display EOTF
Can be displayed unprocessed on SDR screen
•
•
•
• In TV Production HLG can use existing SDR infrastructure and monitoring displays
•
Only critical monitoring requires HDR displays
• Both HLG and PQ included in ITU-R Recommendation BT.2100
• Both HLG and PQ include in DVB, ARIB and YouTube for HDR TV Distribution
An Overview of the Hybrid Log-Gamma HDR System
Thank you
bbc.co.uk/rd
bbc.co.uk/rd/projects/high-dynamic-range
Email:
Twitter:
tim.borer@bbc.co.uk
andrew.cotton@bbc.co.uk
@bbcrd
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