ISO/IEC TR 23008-15:2018

Information technology — High efficiency coding and media delivery in heterogeneous environments — Part 15: Signalling, backward compatibility and display adaptation for HDR/WCG video

This document reviews approaches for processing and coding of HDR/WCG video content. The purpose of this document is to provide a set of publicly-referenceable methods for the operation of AVC or HEVC video coding systems adapted for compressing HDR/WCG video for consumer distribution applications. This document first includes a review of the video usability information (VUI) indicators and supplemental enhancement information (SEI) messages applicable for HDR/WCG video. It provides a description of processing steps for converting from 4:4:4 RGB linear light representation video signals into video signals with ICTCP colour representation and perceptual quantizer (PQ) transfer function, or with Y′CbCr colour representation and HLG transfer function (ICTCP, PQ and HLG are defined in Rec. ITU-R BT.2100-1). Some high-level approaches for compressing these signals using either Rec. ITU-T H.264 | ISO/IEC 14496-10 or Rec. ITU-T H.265 | ISO/IEC 23008-2 are provided. A description of post-decoding processing steps is also included for converting back to a linear light, 4:4:4 RGB representation. The document also addresses the standard dynamic range (SDR) backward compatibility, that is, the compatibility with legacy decoding systems that are not able to detect and properly display HDR/WCG video content. It describes example implementations of this feature using three different solutions: using HLG as a backward compatible transfer function, using CRI and TMI SEI messages, using dual-layer approach with the Scalable Main 10 profile of HEVC and an SDR compatible base layer. Finally, the document illustrates the usage of CRI SEI messages to convey metadata enabling the dynamic range and colour gamut adaptation at the display side of the decoded video to the display capabilities. NOTE The document complements the material provided in ITU-T H.Sup15 | ISO/IEC TR 23008-14, which is focused on conversion and coding practices for non-constant luminance (NCL) Y′CbCr video signals using the PQ transfer function.

Technologies de l'information — Codage à haut rendement et fourniture de supports dans les environnements hétérogènes — Partie 15: Signalisation, compatibilité amont et adaptation de l'affichage pour la vidéo HDR/WCG

General Information

• Status: Published
• Publication Date: 06-Aug-2018
• ICS: 35.040.40 - Coding of audio, video, multimedia and hypermedia information
• Technical Committee: ISO/IEC JTC 1/SC 29 - Coding of audio, picture, multimedia and hypermedia information
• Drafting Committee: ISO/IEC JTC 1/SC 29 - Coding of audio, picture, multimedia and hypermedia information
• Current Stage: 6060 - International Standard published
• Start Date: 07-Aug-2018
• Due Date: 21-Oct-2019
• Completion Date: 21-Oct-2019

Overview

ISO/IEC TR 23008-15:2018 is a technical report that documents signalling, processing and backward‑compatibility approaches for high dynamic range (HDR) and wide colour gamut (WCG) video in consumer distribution. It surveys relevant VUI indicators and SEI messages, describes conversion chains from linear 4:4:4 RGB to HDR/WCG coding representations (ICTCP+PQ and Y′CbCr+HLG), proposes high‑level encoding approaches for AVC (H.264) and HEVC (H.265), and explains post‑decode conversion back to linear RGB. The report also details methods to enable SDR backward compatibility and display‑side dynamic range and gamut adaptation.

Key topics

• Signalling and metadata
  • Review of applicable VUI syntax elements and SEI messages such as Mastering Display Colour Volume, Content Light Level, Ambient Viewing Environment, Alternative Transfer Characteristics, Tone Mapping Information (TMI) and Colour Remapping Information (CRI).
• Colour and transfer conversions
  • Conversion workflows from linear 4:4:4 RGB to ICTCP with PQ EOTF (Perceptual Quantizer) or to Y′CbCr with HLG (Hybrid Log‑Gamma).
  • Reference descriptions for PQ and HLG transfer functions (per Rec. ITU‑R BT.2100‑1).
• Encoding workflows
  • High‑level guidance for compressing HDR/WCG signals using HEVC and, when applicable, AVC.
  • Pre‑encoding, encoding and post‑decoding processing stages to preserve HDR/WCG intent.
• SDR backward compatibility
  • Three example solutions: use of HLG as a natively backward‑compatible transfer function; dynamic signalling using CRI and TMI SEI messages; and a dual‑layer approach using HEVC Scalable Main 10 profile with an SDR‑compatible base layer.
• Display adaptation
  • Use of CRI SEI metadata to enable dynamic range and colour‑gamut adaptation on displays according to device capabilities.

Applications

This TR is practical for professionals who implement or integrate HDR/WCG workflows:

• Video codec and encoder/decoder developers implementing HEVC/AVC HDR signalling and processing.
• Content creators and post‑production engineers preparing HDR/WCG masters and metadata.
• Broadcasters, OTT platform engineers and system integrators designing distribution chains that must support mixed HDR/SDR device ecosystems.
• Display manufacturers and firmware developers implementing display adaptation using CRI/TMI metadata.
• Standards and interoperability test labs validating HDR/WCG signalling and SDR compatibility.

Related standards

• Rec. ITU‑R BT.2100 (ICTCP, PQ, HLG) - referenced for colour and transfer definitions.
• ISO/IEC 23008‑2 / Rec. ITU‑T H.265 (HEVC) - signalling mechanisms and SEI message usage.
• ISO/IEC 14496‑10 / Rec. ITU‑T H.264 (AVC) - when applicable for coding approaches.
• ISO/IEC TR 23008‑14 (ITU‑T H.Sup15) - complementary guidance focused on PQ coding practices for NCL Y′CbCr signals.

Keywords: ISO/IEC TR 23008-15:2018, HDR, WCG, HEVC, AVC, PQ, HLG, ICTCP, SEI, CRI, TMI, SDR backward compatibility, display adaptation, colour remapping, tone mapping.

Standards Content (Sample)

TECHNICAL ISO/IEC TR
REPORT 23008-15
First edition
2018-08
Information technology — High
efficiency coding and media delivery
in heterogeneous environments —
Part 15:
Signalling, backward compatibility and
display adaptation for HDR/WCG video
Technologies de l'information — Codage à haut rendement et
fourniture de supports dans les environnements hétérogènes —
Partie 15: Signalisation, compatibilité amont et adaptation de
l'affichage pour la vidéo HDR/WCG
Reference number
©
ISO/IEC 2018
© ISO/IEC 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2018 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 3
5 Conventions . 4
5.1 General . 4
5.2 Arithmetic operators . 5
5.3 Bit-wise operators. 5
5.4 Assignment operators . 6
5.5 Relational, logical and other operators . 6
5.6 Mathematical functions . 6
5.7 Order of operations . 7
6 Overview . 8
7 HEVC signalling mechanisms applicable to HDR/WCG video . 9
7.1 General . 9
7.2 VUI syntax elements . 9
7.3 SEI messages applicable for HDR/WCG video .10
7.3.1 General.10
7.3.2 Mastering display colour volume SEI message . .10
7.3.3 Content light level information SEI message .11
7.3.4 Ambient viewing environment SEI message .11
7.3.5 Alternative transfer characteristics SEI message .11
7.3.6 Tone mapping information SEI message .11
7.3.7 Colour remapping information SEI message .12
7.4 Overview of PQ and HLG transfer functions .13
7.4.1 General.13
7.4.2 Reference PQ EOTF .14
7.4.3 Reference HLG OETF .15
7.5 IC C colour representation .16
T P
7.5.1 General.16
7.5.2 Pre-encoding process .17
7.5.3 Encoding process . .20
7.5.4 Decoding process .22
7.5.5 Post-decoding process .22
8 Bitstream SDR backward compatibility with single-layer coding .24
8.1 General .24
8.2 Approach 1: usage of HLG for “static” bitstream SDR backward compatibility .24
8.2.1 General.24
8.2.2 HLG pre-encoding conversion process .25
8.2.3 Encoding process . .27
8.2.4 Decoding process .29
8.2.5 HLG post-decoding conversion .29
8.2.6 Colour representation conversion: Y′CbCr to R′G′B′ .30
8.3 Approach 2: usage of SEI messages for “dynamic” bitstream SDR backward
compatibility .30
8.3.1 General.30
8.3.2 CRI applied in Y′CbCr 4:2:0 domain .31
8.3.3 CRI applied in Y′CbCr 4:4:4 domain .32
8.3.4 TMI applied in R′G′B′ 4:4:4 domain .33
© ISO/IEC 2018 – All rights reserved iii

8.3.5 Derivation of DRA functions .34
8.3.6 Settings with colour remapping information SEI message .35
8.3.7 Settings with tone mapping information SEI message .36
9 Bitstream SDR backward compatibility with dual-layer SHVC coding .37
9.1 General .37
9.2 Encoding and decoding stages .37
10 Display adaptation.39
10.1 General .39
10.2 Display SDR backward compatibility .39
10.2.1 Conversion and coding process example .39
10.2.2 Using colour remapping information SEI message .41
Bibliography .43
iv © ISO/IEC 2018 – All rights reserved

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical
activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work. In the field of information technology, ISO and IEC have established a joint technical committee,
ISO/IEC JTC 1.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information, in collaboration
with ITU-T. A technically aligned twin text is published as ITU-T H.Sup18.
A list of all parts in the ISO/IEC 23008 series can be found on the ISO website.
© ISO/IEC 2018 – All rights reserved v

Introduction
High dynamic range (HDR) video is a type of video content in which the sample values represent a
larger luminance range than conventional standard dynamic range (SDR) video. HDR video can provide
an enhanced viewer experience and can more accurately reproduce scenes that include, within the
same image, dark areas and bright highlights, such as emissive light sources and reflections. Wide
colour gamut (WCG) video, on the other hand, is video characterized by a wider spectrum of colours
compared to what has been commonly available in conventional video. Recent advances in capture and
display technology have enabled consumer distribution of HDR and WCG content. However, given the
characteristics of such content, special considerations may need to be made, in terms of both processing
and compression, compared to conventional content.
This document relates to HDR/WCG video coding and distribution, using single-layer or dual-layer
coding, with the signalling specified for Rec. ITU-T H.265 | ISO/IEC 23008-2 High efficiency video coding
(HEVC), and when applicable, Rec. ITU-T H.264 | ISO/IEC 14496-10 Advanced video coding (AVC).
This document serves several purposes:
— It provides a survey of identified video usability information (VUI) syntax elements and supplemental
enhancement information (SEI) messages specified in HEVC and AVC applicable for HDR/WCG video.
— It covers conversion and coding chains using the IC C colour representation, and the hybrid log-
T P
gamma (HLG) transfer functions.
— Examples of using colour remapping information (CRI) and tone mapping information (TMI) SEI
messages for the support of SDR backward compatibility and display adaptation functionalities are
described.
— A dual-layer coding approach using the Scalable Main 10 profile of HEVC for backward compatibility
with SDR systems is also documented.
vi © ISO/IEC 2018 – All rights reserved

TECHNICAL REPORT ISO/IEC TR 23008-15:2018(E)
Information technology — High efficiency coding and
media delivery in heterogeneous environments —
Part 15:
Signalling, backward compatibility and display adaptation
for HDR/WCG video
1 Scope
This document reviews approaches for processing and coding of HDR/WCG video content. The purpose
of this document is to provide a set of publicly-referenceable methods for the operation of AVC or HEVC
video coding systems adapted for compressing HDR/WCG video for consumer distribution applications.
This document first includes a review of the video usability information (VUI) indicators and
supplemental enhancement information (SEI) messages applicable for HDR/WCG video. It provides a
description of processing steps for converting from 4:4:4 RGB linear light representation video signals
into video signals with IC C colour representation and perceptual quantizer (PQ) transfer function,
T P
or with Y′CbCr colour representation and HLG transfer function (IC C , PQ and HLG are defined in Rec.
T P
ITU-R BT.2100-1). Some high-level approaches for compressing these signals using either Rec. ITU-T
H.264 | ISO/IEC 14496-10 or Rec. ITU-T H.265 | ISO/IEC 23008-2 are provided. A description of post-
decoding processing steps is also included for converting back to a linear light, 4:4:4 RGB representation.
The document also addresses the standard dynamic range (SDR) backward compatibility, that is, the
compatibility with legacy decoding systems that are not able to detect and properly display HDR/WCG
video content. It describes example implementations of this feature using three different solutions:
using HLG as a backward compatible transfer function, using CRI and TMI SEI messages, using dual-
layer approach with the Scalable Main 10 profile of HEVC and an SDR compatible base layer. Finally, the
document illustrates the usage of CRI SEI messages to convey metadata enabling the dynamic range
and colour gamut adaptation at the display side of the decoded video to the display capabilities.
NOTE The document complements the material provided in ITU-T H.Sup15 | ISO/IEC TR 23008-14, which is
focused on conversion and coding practices for non-constant luminance (NCL) Y′CbCr video signals using the PQ
transfer function.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
Recommendation ITU-T H.264 | ISO/IEC 14496-10: 2014, Information technology — Coding of audio-
visual objects — Part 10: Advanced Video Coding
Recommendation ITU-T H.265 | ISO/IEC 23008-2: 2017, Information technology — High efficiency coding
and media delivery in heterogeneous environments — Part 2: High efficiency video coding
3 Terms and definitions
For the purposes of this document, the terms and definitions given in Rec. ITU-T H.264 | ISO/IEC 14496-
10, Rec. ITU-T H.265 | ISO/IEC 23008-2, and the following apply.
© ISO/IEC 2018 – All rights reserved 1

ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1
dynamic range adaptation
DRA
mapping process to convert content from one colour volume to another colour volume
3.2
electro-optical transfer function
EOTF
function which converts a non-linear video signal into a quantity of output linear light
Note 1 to entry: An example of output linear light is light emitted by a display.
3.3
full range
range in a fixed-point (integer) representation that spans the full range of values that could be
expressed with that bit depth, such that, for 10-bit signals, black corresponds to code value 0 and peak
white corresponds to code value 1023 for Y′
Note 1 to entry: As per the full range definition from Rec. ITU-R BT.2100-1.
3.4
hybrid log-gamma
HLG
one set of transfer functions offering a degree of compatibility with legacy displays by more closely
matching the previously established television transfer curves
Note 1 to entry: Sets of transfer functions related to HDR signals are specified in Rec. ITU-R BT.2100-1.
3.5
narrow range
range in a fixed-point (integer) representation that does not span the full range of values that could be
expressed with that bit depth such that, for 10-bit representations, the range from 64 (black) to 940
(peak white) is used for Y′ and the range from 64 to 960 is used for Cb and Cr
Note 1 to entry: As per the narrow range definition from Rec. ITU-R BT.2100-1.
3.6
opto-electronic transfer function
OETF
function which converts a source input linear optical intensity into a non-linear video signal
Note 1 to entry: An example of input linear optical intensity is light input to a camera.
3.7
opto-optical transfer function
OOTF
function which has the role of applying the “rendering intent” on video signal
Note 1 to entry: In general, an OOTF is a concatenation of an OETF, artistic adjustments and an EOTF.
2 © ISO/IEC 2018 – All rights reserved

3.8
perceptual quantizer
PQ
one set of transfer functions achieving a very wide range of brightness levels for a given bit depth using
a non-linear transfer function that is finely tuned to match the human visual system
Note 1 to entry: Sets of transfer functions related to HDR signals are specified in Rec. ITU-R BT.2100-1.
3.9
random access point access unit
RAPAU
access unit in the bitstream at which the initiation of the decoding process for some or all subsequent
pictures in the bitstream is intended to be feasible
3.10
reference electro-optical transfer function
reference EOTF
specified EOTF for use under specific viewing environment, named the reference viewing environment
3.11
reference opto-electronic transfer function
reference OETF
specified OETF implemented within cameras, to ensure consistency of the image between cameras
from different manufacturers
3.12
reference viewing environment
parameters to establish a reproducible viewing environment for critical viewing of material that can
provide repeatable results from one facility to another when viewing the same material
Note 1 to entry: Rec. ITU-R BT.2100-1:2017, Table 3 provides reference viewing environment parameters for HDR
programme material.
4 Abbreviated terms
For the purposes of this document, the abbreviated terms given in Rec. ITU-T H.264 | ISO/IEC 14496-10,
Rec. ITU-T H.265 | ISO/IEC 23008-2 and the following apply.
ATC alternative transfer characteristics
AVC advanced video coding, specified in Rec. ITU-T H.264 | ISO/IEC 14496-10
AVE ambient viewing environment
CGS colour gamut scalability
CI constant intensity
CL constant luminance
CLL content light level
CLVS coded layer-wise video sequence
CRI colour remapping information
FIR finite impulse response
HDR high dynamic range
© ISO/IEC 2018 – All rights reserved 3

HEVC high efficiency video coding, specified in Rec. ITU-T H.265 | ISO/IEC 23008-2
IC C alternative colour space representation to Y′CbCr, specified in Rec. ITU-R BT.2100-1
T P
LMS long, medium, and short wavelength-based colour space, specified in Rec. ITU-R BT.2100-1
LUT look-up table
MAD mean absolute difference
MDCV mastering display colour volume
NCL non-constant luminance
PQ10 HDR content representation that utilizes the Rec. ITU-R BT.2100-1 colour primaries, the Rec.
ITU-R BT.2100-1 reference PQ EOTF, and the Rec. ITU-R BT.2100-1 Y′CbCr colour space rep-
resentation with 10 bits per sample in the 4:2:0 chroma sampling format
QP quantization parameter
RGB colour system using red, green, and blue components
SDR standard dynamic range
SEI supplemental enhancement information
SHVC scalable high efficiency video coding
SPS sequence parameter set
SSE sum of squared errors
TMI tone mapping information
UHD ultra-high definition
VUI video usability information
WCG wide colour gamut
XYZ CIE 1931 colour space; Y corresponds to the luminance signal
Y′CbCr colour space representation commonly used for video/image distribution as a way of encod-
ing RGB information, also commonly expressed as YCbCr, Y′C C , or Y′C′ C′
B R B R
[The relationship between Y′CbCr and RGB is dictated by certain signal parameters, such
as colour primaries, transfer characteristics, and matrix coefficients. Unlike the (constant
luminance) Y component in the XYZ representation, Y′ in this representation might not be
representing the same quantity. Y′ is commonly referred to as “luma”. Cb and Cr are com-
monly referred to as “chroma”.]
5 Conventions
5.1 General
The mathematical operators used in this document are similar to those used in the C programming
language. However, the results of integer division and arithmetic shift operations are defined more
precisely, and additional operations are defined, such as exponentiation and real-valued division.
Numbering and counting conventions generally begin from 0, e.g., “the first” is equivalent to the 0-th,
“the second” is equivalent to the 1-th, etc.
4 © ISO/IEC 2018 – All rights reserved

5.2 Arithmetic operators
+ addition
− subtraction (as a two-argument operator) or negation (as a unary prefix operator)
* multiplication, including matrix multiplication
exponentiation
y
(Denotes x to the power of y. In other contexts, such notation is used for superscripting not
x
intended for interpretation as exponentiation.)
integer division with truncation of the result toward zero
/
[For example, 7/4 and (−7)/(−4) are truncated to 1 and (−7)/4 and 7/(−4) are truncated to −1.]
÷ division in mathematical formulae where no truncation or rounding is intended
x
division in mathematical formulae where no truncation or rounding is intended
y
y
fi summation of f( i ) with i taking all integer values from x up to and including y
()
∑
i=x
modulus
x % y
(Remainder of x divided by y, defined only for integers x and y with x >= 0 and y > 0.)
5.3 Bit-wise operators
bit-wise “and”
(When operating on integer arguments, operates on a two’s complement representation of
&
the integer value. When operating on a binary argument that contains fewer bits than anoth-
er argument, the shorter argument is extended by adding more significant bits equal to 0.)
bit-wise “or”
(When operating on integer arguments, operates on a two’s complement representation of
|
the integer value. When operating on a binary argument that contains fewer bits than anoth-
er argument, the shorter argument is extended by adding more significant bits equal to 0.)
bit-wise “exclusive or”
(When operating on integer arguments, operates on a two’s complement representation of
^
the integer value. When operating on a binary argument that contains fewer bits than anoth-
er argument, the shorter argument is extended by adding more significant bits equal to 0.)
arithmetic right shift of a two’s complement integer representation of x by y binary digits
x >> y (This function is defined only for non-negative integer values of y. Bits shifted into the MSBs
as a result of the right shift have a value equal to the MSB of x prior to the shift operation.)
arithmetic left shift of a two’s complement integer representation of x by y binary digits
x << y (This function is defined only for non-negative integer values of y. Bits shifted into the LSBs
as a result of the left shift have a value equal to 0.)
© ISO/IEC 2018 – All rights reserved 5

5.4 Assignment operators
= assignment operator
increment, i.e., x++ is equivalent to x = x + 1; when used in an array index, evaluates to the
++
value of the variable prior to the increment operation
decrement, i.e., x−− is equivalent to x = x − 1; when used in an array index, evaluates to the
−−
value of the variable prior to the decrement operation
increment by amount given, i.e., x += 3 is equivalent to x = x + 3, and x += (−3) is equivalent
+=
to x = x + (−3)
decrement by amount given, i.e., x −= 3 is equivalent to x = x − 3, and x −= (−3) is equivalent
−=
to x = x − (−3)
5.5 Relational, logical and other operators
== equality operator
!= not equal to operator
!x logical negation “not”
> larger than operator
< smaller than operator
>= larger than or equal to operator
<= smaller than or equal to operator
conditional/logical “and” operator
&& (Performs a logical “and” of its Boolean operators, but only evaluates the second operand if
necessary.)
conditional/logical “or” operator
| | (Performs a logical “or” of its Boolean operators, but only evaluates the second operand if
necessary.)
ternary conditional
a ? b : c
(If condition a is true, then the result is equal to b; otherwise the result is equal to c.)
5.6 Mathematical functions
 xx; >=0

Absx =
()

− 

smallest integer greater than or equal to x
Ceil x
()
xz; 
Clip3,xy,z = yz; >y
()


zo; therwise

6 © ISO/IEC 2018 – All rights reserved

reference PQ EOTF used to convert a non-linear light PQ representation to a line-
EOTF x
()
PQ
ar light representation
x where e is Euler’s base constant 2.718 281 828.
Expx =e
()
largest integer less than or equal to x
Floor x
()
inverse reference PQ EOTF used to convert a linear light representation to a
iEOTFx
()
PQ
non-linear light representation
inverse reference HLG OETF used to convert a non-linear light representation to
iOETF x
()
HLG
a scene-referred linear light representation
natural logarithm of x (the base-e logarithm, where e is natural logarithm base
Ln x
()
constant 2.718 281 828….)
base-10 logarithm of x
Log10x
()
xx; > y

Maxx(),y =

yo; therwise


reference HLG OETF used to convert a scene-referred linear light representation
OETF x
()
HLG
to a non-linear light representation
Roundx =Sign x*FloorAbs x +05.
() () ()()
 10; x>

Sign x = 00; x=
()


−<10; x

Sqrt xx=
()
5.7 Order of operations
When order of precedence in an expression is not indicated explicitly by use of parentheses, the
following rules apply:
— Operations of a higher precedence are evaluated before any operation of a lower precedence.
— Operations of the same precedence are evaluated sequentially from left to right.
Table 1 specifies the precedence of operations from highest to lowest; a higher position in the table
indicates a higher precedence.
NOTE For those operators that are also used in the C programming language, the order of precedence used
in this document is the same as used in the C programming language.
Table 1 — Operation precedence from highest (at top of table) to lowest (at bottom of table)
Operations (with operands x, y, and z)
“x++”, “x−−”
“!x”, “−x” (as a unary prefix operator)
y
“x ”
© ISO/IEC 2018 – All rights reserved 7

Table 1 (continued)
Operations (with operands x, y, and z)
x
“x * y”, “x / y”, “x ÷ y”, “ ”, “x % y”
y
y
“x + y”, “x − y” (as a two-argument operator), “ fi ”
()
∑
i=x
“x << y”, “x >> y”
“x < y”, “x <= y”, “x > y”, “x >= y”
“x = = y”, “x != y”
“x & y”
“x | y”
“x && y”
“x | | y”
“x ? y : z”
“x.y”
“x = y”, “x += y”, “x −= y”
6 Overview
This document is structured as follows.
— Clause 7 reviews identified signalling mechanisms of HEVC, and when applicable, of AVC, relevant
for HDR/WCG video coding and distribution. It also describes some common processing steps used
in end-to-end processing chains such as described in Clauses 8 and 9.
— Clause 8 describes usage of HLG transfer functions and CRI or TMI SEI messages for the support of
bitstream SDR backward compatibility (defined below) with a single-layer profile (e.g. HEVC Main 10).
— Clause 9 describes a dual-layer HDR/WCG video coding system with bitstream SDR backward
compatibility implemented with the HEVC Scalable Main 10 profile.
— Clause 10 addresses the display adaptation functionality (defined below), with application examples
based on the CRI SEI message. This clause includes the specific case of display SDR backward
compatibility.
“SDR backward compatibility” relates to the ability of HDR/WCG video coding and distribution systems
to produce a video signal suitable for SDR-only capable rendering devices (e.g. UHD SDR display with
Rec. ITU-R BT.2020-2 colour primaries). In the present document, it is defined in two modes: bitstream
and display.
— In HDR/WCG distribution systems that support “bitstream” SDR backward compatibility, the
decoded video signal from a standard-compliant decoder (e.g. HEVC Main 10 decoder) can be
directly displayed on an SDR-capable display without adaptation. Two categories of “bitstream”
SDR backward compatibility are considered:
— In “static” bitstream SDR backward compatibility, the decoded video is an HDR signal, for
instance, Y′CbCr 4:2:0 10-bits with the Rec. ITU-R BT.2100-1 reference HLG opto-electronic
transfer function (OETF) and Rec. ITU-R BT.2100-1 colour primaries, that can be directly
displayed on an HDR-capable display or an SDR-capable display, without adaptation. In this
context, the HDR processing chain is static, and not dependent on the input video data.
— In “dynamic” bitstream SDR backward compatibility, the decoded video is an SDR signal. A post-
processing step can be further used to reconstruct an HDR signal, using metadata conveyed for
8 © ISO/IEC 2018 – All rights reserved

instance in CRI or TMI SEI messages. In this context, the HDR processing chain is dynamic, and
adapts to the input video data.
— In HDR/WCG distribution systems that support “display” SDR backward compatibility, the decoded
video signal from a standard-compliant decoder (e.g. HEVC Main 10 decoder) is an HDR signal
(for instance, Y′CbCr 4:2:0 10-bits with Rec. ITU-R BT.2100-1 inverse reference PQ electro-optical
transfer function (EOTF) and Rec. ITU-R BT.2100-1 colour primaries). A post-decoding dynamic
range adaptation (DRA) process is applied to the decoded video signal to produce an SDR video
signal that can be displayed on an SDR-capable display. The adaptation process can use metadata,
conveyed for example in CRI SEI messages, to perform this conversion.
“Display adaptation” is a generic term covering techniques of video signal processing which adapt the
decoded video signal to a target display. Techniques providing display SDR backward compatibility are
considered as a subset of display adaptation. Display adaptation techniques aim at converting an HDR/
WCG video signal, originally produced for a reference display capable of displaying a certain colour
volume (dynamic range and colour gamut), to a video signal suitable to a target rendering device of
colour volume capabilities different from the reference display capabilities. For instance, it can be
used to convert a Y′CbCr 4:2:0 10-bits Rec. ITU-R BT.2100-1 PQ signal (denoted PQ10 in the present
document), originated from an HDR video master produced on a display with a given reference peak
luminance, to a lower peak luminance capable display. Display adaptation could also increase the colour
volume, if desired. Another term used in the industry for display adaptation is regrading. Display
adaptation can be driven by metadata transmitted along with the video bitstream, for instance using
SEI messages.
Conversion and coding practices related to production and compression of HDR/WCG video signal
represented with NCL Y′CbCr 4:2:0 video with Rec. ITU-R BT.2100-1 PQ transfer characteristics are
outside of scope of this document. These aspects are specifically addressed in ITU-T H.Sup15 | ISO/
IEC TR 23008-14.
7 HEVC signalling mechanisms applicable to HDR/WCG video
7.1 General
This clause provides an overview of the VUI syntax elements and SEI messages specified in HEVC
(Rec. ITU-T H.265 | ISO/IEC 23008-2), applicable to HDR/WCG video and relevant to the scope of this
document. The PQ, HLG transfer functions, and the IC C colour representation are also described.
T P
This clause is structured as follows.
— Subclause 7.2 reviews VUI signalling applicable to HDR/WCG video.
— Subclause 7.3 reviews SEI messages applicable to HDR/WCG video.
— Subclause 7.4 provides an overview of PQ and HLG transfer functions.
— Subclause 7.5 provides a description of IC C colour representation, including conversion and
T P
coding practices related to HDR/WCG video signals represented with IC C 4:2:0 video with Rec.
T P
ITU-R BT.2100-1 inverse reference PQ EOTF.
Conversion and coding practices related to HDR/WCG video signals represented with Y′CbCr 4:2:0
video with Rec. ITU-R BT.2100-1 HLG transfer characteristics are discussed in subclause 8.2.
7.2 VUI syntax elements
By design, metadata signalled in syntax elements of VUI is not necessary for constructing the luma or
chroma samples by the decoding process, and may be ignored by the decoder. However, such syntax
elements provide useful parameters or attributes of an encoded signal and can be utilized in the video
system design. Examples of VUI parameters relevant to HDR/WCG video system design include colour
primaries, transfer characteristics and matrix coefficients specified in Rec. ITU-T H.265 | ISO/IEC
© ISO/IEC 2018 – All rights reserved 9

23008-2:2017, Tables E.3, E.4 and E.5 respectively. Table 2 and Table 3 provide values of VUI syntax
elements that indicate usage of Rec. ITU-R BT.2100-1 representation of the video signal, including matrix
coefficients associated with Rec. ITU-R BT.2100-1 (same as those associated with Rec. ITU-R BT.2020-2).
Rec. ITU-R BT.2100-1 specifies HDR-TV image parameters for use in production and international
programme exchange. It defines two sets of transfer functions: perceptual quantizer (PQ) and hybrid
log-gamma (HLG). RGB colour primaries are defined identically as in Rec. ITU-R BT.2020-2. Rec. ITU-R
BT.2100-1 describes two different luminance and colour difference signal representations: non-
constant luminance (NCL) Y′CbCr and constant intensity (CI) IC C . Syntax elements of VUI in HEVC
T P
can be used to convey the metadata describing such attributes of the coded signal. The VUI transfer_
characteristics syntax element either indicates the reference OETF of the source picture as a function
of a source input linear optical intensity or indicates the inverse of the reference EOTF as a function of
an output linear optical intensity, as described in Table 2 for HEVC. RGB colour primaries are indicated
using colour_primaries syntax element (set equal to 9 for Rec. ITU-R BT.2100-1/Rec. ITU-R BT.2020-2
colour primaries). Colour representation is indicated using matrix_coeffs syntax element, as described
in Table 3 for HEVC.
Table 2 — Values of transfer_characteristics indication in VUI in HEVC
PQ HLG
transfer_characteristics 16 18
Table 3 — Values of matrix_coeffs indication in VUI in HEVC
NCL Y′CbCr CI IC C
T P
matrix_coeffs 9 14
NOTE 1 PQ is also defined in SMPTE ST 2084 and HLG is also defined in ARIB STD-B67.
NOTE 2 VUI syntax element values for PQ are also defined in AVC.
7.3 SEI messages applicable for HDR/WCG video
7.3.1 General
SEI messages assist in processes related to decoding, display or other purposes. They are not required
for constructing the luma or chroma samples by the decoding process. HEVC and AVC specify several
SEI messages applicable to HDR/WCG video. Some SEI messages convey descriptive information about
the content. These SEI messages are reviewed in subclauses 7.3.2 to 7.3.5. Some other SEI messages are
devoted to enabling specific post-processing of the decoded samples, e.g. signal adaptation processes.
Some SEIs can be used for the conversion of decoded content from one colour volume to another colour
volume. For example, this approach can apply in bitstream SDR backward compatibility use cases for
SDR-to-HDR conversion (the decoded signal is SDR, and the converted signal after post-processing
using metadata conveyed in the SEI message is HDR). This approach can also apply in display adaptation
use cases for converting a decoded HDR signal to an HDR version of a different colour volume. This
comprises conversion to an SDR version for display SDR backward compatibility use case. These various
SEI messages are described in subclauses 7.3.6 and 7.3.7.
7.3.2 Mastering display colour volume SEI message
The mastering display colour volume (MDCV) SEI message specifies the colour gamut and dynamic
range of a hypothetical monitor used for viewing while authoring the video content. It conveys the colour
primaries and white point of the monitor, expressed in the CIE 1931 xyY colour space (ISO 11664-1), and
provides the minimum and maximum linear light luminance of the monitor (expressed in candelas per
square metre, denoted cd/m ). The indicative information provided by MDCV may assist the receiving
system in adapting the received video content for local display with characteristics that may differ
from the assumed mastering display characteristics. The MDCV SEI message persists until the end of
10 © ISO/IEC 2018 – All rights reserved

the CLVS. The HEVC specification requires that all MDCV SEI messages that apply to the same CLVS
have the same content.
NOTE 1 The mastering display colour volume SEI message is also defined in AVC.
NOTE 2 Mastering display colour volume metadata is also defined in SMPTE ST 2086.
7.3.3 Content light level information SEI message
The content light level information (CLL) SEI message conveys the maximum light level and average
light level, in the linear light domain (expressed in cd/m ), among the 4:4:4 R, G, B samples of the
content pictures in the coded video sequence. As for the MDCV SEI message, the indicative information
provided by CLL SEI message may assist the receiving system in adapting the received video content to
local display capabilities. It can be used for instance to help better controlling the energy consumption
for local display (see Reference [12]). The CLL SEI message persists until the end of the CLVS. Rec. ITU-T
H.265 | ISO/IEC 23008-2 requires that all CLL SEI messages that apply to the same CLVS have the same
content.
NOTE 1 The content light level information SEI message is also defined in AVC.
NOTE 2 Corresponding metadata associated with the CLL SEI message and examples of derivation algorithms
are defined in CEA-861.3.
7.3.4 Ambient viewing environment SEI message
The ambient viewing environment (AVE) SEI message characterizes the ambient viewing environment
assumed when mastering the associated video content. It conveys the environmental illuminance and
chromaticity coordinates (in the CIE 1931 xyY colour space) of the mastering nominal ambient viewing
environment. This indicative information may assist the receiving system in adapting the received
video content for local display in viewing environments that may differ from those assumed when
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