Bsi bs en 61966 2 4 2006

BRITISH STANDARD

Multimedia systems
and equipment —
Colour measurement
and management —
Part 2–4: Colour management —
Extended-gamut YCC colour space
for video applications — xvYCC

The European Standard EN 61966-2-4:2006 has the status of a
British Standard

ICS 33.160.40

12&23<,1*:,7+287%6,3(50,66,21(;&(37$63(50,77('%<&23<5,*+7/$:

BS EN
61966-2-4:2006


BS EN 61966-2-4:2006

National foreword
This British Standard was published by BSI. It is the UK implementation of
EN 61966-2-4:2006. It is identical with IEC 61966-2-4:2006.
The UK participation in its preparation was entrusted to Technical Committee
EPL/100, Audio, video and multimedia systems and equipment.
A list of organizations represented on EPL/100 can be obtained on request to
its secretary.
This publication does not purport to include all the necessary provisions of a

contract. Users are responsible for its correct application.
Compliance with a British Standard cannot confer immunity from
legal obligations.

This British Standard was
published under the authority
of the Standards Policy and
Strategy Committee
on 31 October 2006

© BSI 2006

ISBN 0 580 49415 2

Amendments issued since publication
Amd. No.

Date

Comments


EN 61966-2-4

EUROPEAN STANDARD
NORME EUROPÉENNE

September 2006

EUROPÄISCHE NORM

ICS 33.160.40

English version

Multimedia systems and equipment Colour measurement and management
Part 2-4: Colour management Extended-gamut YCC colour space for video applications xvYCC
(IEC 61966-2-4:2006)
Mesure et gestion de la couleur
dans les systèmes et appareils multimedia
Partie 2-4 : Gestion de la couleur Extension de gamme de l'espace
chromatique YCC pour
applications vidéo xvYCC
(CEI 61966-2-4:2006)

Multimediasysteme und -geräte Farbmessung und Farbmanagement
Teil 2-4: Farbmanagement Erweiterter YCC-Farbraum
für Videoanwendungen xvYCC
(IEC 61966-2-4:2006)

This European Standard was approved by CENELEC on 2006-09-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.
This European Standard exists in two official versions (English and German). A version in any other language
made by translation under the responsibility of a CENELEC member into its own language and notified to the
Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2006 CENELEC -

All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61966-2-4:2006 E


EN 61966-2-4:2006

–2–

Foreword
The text of the International Standard IEC 61966-2-4:2006, prepared by IEC TC 100, Audio, video and
multimedia systems and equipment, was submitted to the formal vote and was approved by CENELEC as
EN 61966-2-4 on 2006-09-01 without any modification.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement

(dop)

2007-06-01

– latest date by which the national standards conflicting
with the EN have to be withdrawn

(dow)

2009-09-01

__________

Endorsement notice
The text of the International Standard IEC 61966-2-4:2006 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 61966-2-1
+ A1

NOTE Harmonized as EN 61966-2-1:2000 + A1:2003 (not modified).

IEC 61966-2-2

NOTE Harmonized as EN 61966-2-2:2003 (not modified).

__________


INTERNATIONAL
STANDARD

IEC
61966-2-4

First edition
2006-01

Multimedia systems and equipment –
Colour measurement and management –
Part 2-4:
Colour management –
Extended-gamut YCC colour space
for video applications – xvYCC

Reference number
IEC 61966-2-4:2006(E)


EN 61966-2-4:2006

–4–

CONTENTS

INTRODUCTION.....................................................................................................................5
1

Scope ...............................................................................................................................6

2

Normative references .......................................................................................................6

3

Terms and definitions.........................................................................................................6

4

Colorimetric parameters and related characteristics .........................................................7

5

4.1 Primary colours and reference white........................................................................7
4.2 Opto-electronic transfer characteristics ...................................................................7
4.3 YCC (luma-chroma-chroma) encoding methods .......................................................8
4.4 Digital quantization methods ...................................................................................8
Encoding transformations .................................................................................................9
5.1
5.2
5.3

Introduction .............................................................................................................9
Transformation from xvYCC values to CIE 1931 XYZ values ...................................9
Transformation from CIE 1931 XYZ values to xvYCC values ................................. 11

Annex A (informative) Compression of specular components of Y’ signals ........................... 13
Annex B (informative) Default transformation from 16-bit scRGB values to xvYCC values .... 14
Annex C (informative) xvYCC/ITU-R BT.709 and sYCC/sRGB compatibility ......................... 16
Annex ZA (normative) Normative references to international publications with their
corresponding European publications............................................................................... 19
Bibliography.......................................................................................................................... 18
Figure A.1 – Example of the specular compression method .................................................. 13
Figure C.1 – Relationship between ITU-R BT.709 and sRGB ................................................ 16

Figure C.2 – Relationship between xvYCC and sYCC ........................................................... 17
Table 1 – CIE chromaticities for reference primary colours and reference white ......................7
.


–5–

EN 61966-2-4:2006

INTRODUCTION
After the publication of IEC 61966-2-1, Amendment 1, the sYCC colour encoding was used to
capture, store and print extended colour gamut for still image applications. Users received
pleasant benefit by exchanging and reproducing wide-gamut colour images.
Recently, various kinds of displays that are capable of producing a wider gamut of colour than
the conventional CRT-based displays are emerging. However, most of the current video
contents that are displayed on conventional displays, are rendered for the sRGB-gamut.
Users of wide-gamut displays could benefit from wide-gamut colour images by video colour
encoding that supports a larger colour gamut.
This standard defines the “extended-gamut YCC colour space for video applications”. It is
based on the current implementation of YCC colour encoding that is used in the video industry
(namely ITU-R BT.709-5) and extends its definition to the wider gamut of colour range.


EN 61966-2-4:2006

–6–

MULTIMEDIA SYSTEMS AND EQUIPMENT –
COLOUR MEASUREMENT AND MANAGEMENT –
Part 2-4: Colour management –

Extended-gamut YCC colour space
for video applications – xvYCC

1

Scope

This part of IEC 61966 is applicable to the encoding and communication of YCC colours used
in video systems and similar applications by defining encoding transformations for use in
defined reference capturing conditions. If actual conditions differ from the reference conditions,
additional rendering transformations may be required. Such additional rendering transformations are beyond the scope of this standard.

2

Normative references

The following referenced documents are indispensable for the application 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.
IEC 60050-845:1987, International Electrotechnical Vocabulary (IEV) – Part 845: Lighting
ITU-R Recommendation BT.601-5:1995, Studio encoding parameters of digital television for
standard 4:3 and wide-screen 16:9 aspect ratios
ITU-R Recommendation BT.709-5:2002, Parameter values for the HDTV standards for
production and international programme exchange

3

Terms and definitions

For the purposes of this document, the following terms and definitions, as well as those

concerning illuminance, luminance, tristimulus, and other related lighting terms given in
IEC 60050-845, apply.
3.1
scene-referred colour encoding
representation of estimated colour-space coordinates of the elements of an original scene,
where a scene is defined to be the relative spectral radiance
3.2
output-referred colour encoding
representation of estimated colour-space coordinates of image data that are appropriate for
specified output device and viewing conditions
3.3
extended gamut
colour gamut extending outside that of the standard sRGB CRT display defined in IEC 619662-1


EN 61966-2-4:2006

–7–
3.4
luma
luminance signal as defined by SMPTE/EG28:1993

NOTE 1 To avoid interdisciplinary confusion resulting from the two distinct definitions of luminance, it has been
proposed that the video documents use “luma” for “luminance, television” (i.e., the luminance signal).
NOTE 2 Video systems approximate the lightness response of vision by computing a luma component Y' as a
weighted sum of non-linear (or gamma-corrected) R'G'B' primary components. Luma is often carelessly referred to
as luminance.

4

Colorimetric parameters and related characteristics

This clause defines colorimetric parameters and the related characteristics of reference
capturing devices.
4.1

Primary colours and reference white

The CIE chromaticities for the reference red, green, and blue primary colours, and for
reference white CIE standard illuminant D65, are given in Table 1. These primaries and white
point values are identical to those of ITU-R BT.709-5.
Table 1 – CIE chromaticities for reference primary colours and reference white
Red

Green

Blue

White/D65

x

0,640 0

0,300 0

0,150 0

0,312 7

y

0,330 0

0,600 0

0,060 0

0,329 0

z

0,030 0

0,100 0

0,790 0

0,358 3

4.2

Opto-electronic transfer characteristics

Opto-electronic transfer characteristics are defined as follows.
If

R, G, B ≤ −0 ,018 ,

R ′ = −1,099 × (− R )0,45 + 0,099

G ′ = −1,099 × (− G )0,45 + 0,099
B ′ = −1,099 × (− B )

0,45

If

+ 0,099

−0 ,018 < R, G, B < 0 ,018 ,

R ′ = 4,50 × R
G ′ = 4,50 × G
B ′ = 4,50 × B
If

(1)

(2)

R, G, B ≥ 0 ,018 ,

R ′ = 1,099 × (R )0,45 − 0,099
G ′ = 1,099 × (G )0,45 − 0,099
B ′ = 1,099 × (B )

0,45

− 0,099

(3)


EN 61966-2-4:2006

–8–

where R, G , B is a voltage normalized by reference white level and proportional to the implicit
light intensity that would be detected with a reference camera colour channel; R ′, G ′, B ′ is the
resulting non-linear primary signal.
4.3

YCC (luma-chroma-chroma) encoding methods

The encoding equations from the primary RGB (red-green-blue) signal: R ′, G ′, B ′ to the YCC
(luma-chroma-chroma) signal: Y ′, Cb ′, Cr ′ is defined by the following two methods. It is
important to follow one of the encodings in the specified application.
xvYCC 601 , which is implemented mainly in the SDTV (standard-definition television)
applications as defined in ITU-R BT. 601-5, is defined as follows:
′   0,299 0
 Y601
 ′  
Cb601  = − 0 ,168 7
 Cr601
′   0,500 0

0,587 0
− 0 ,331 3
− 0 ,418 7

0,114 0   R ′
 
0,500 0  G ′
− 0,081 3   B ′

(4)

NOTE The coefficients in equation (4) are from ITU-R BT.601-5 which defines Y’ of YCC to the three decimal
place accuracy. An additional decimal place is defined above to be consistent with the other matrix coefficients
defined in this standard.

xvYCC 709 , which is implemented mainly in the HDTV (high-definition television) applications
as defined in ITU-R BT. 709-5, is defined as follows:
′   0,212 6
 Y709
 ′  
Cb709  = − 0,114 6
 Cr709
′   0 ,500 0
4.4

0,715 2
− 0,385 4
− 0 ,454 2

0 ,072 2   R ′
 
0 ,500 0  G ′
− 0 ,045 8   B ′

(5)

Digital quantization methods

Quantization of YCC (luma-chroma-chroma) signal: Y ′, Cb ′, Cr ′ is defined as follows.
For 8-bit representation:
YxvYCC(8 ) = round[219 × Y ′ + 16 ]

Cb xvYCC(8 ) = round[224 × Cb ′ + 128 ]

(6)

CrxvYCC(8 ) = round[224 × Cr ′ + 128 ]

For n-bit (n > 8) representation:

[
]
= round[(224 × Cb ′ + 128 ) × 2
]
= round[(224 × Cr ′ + 128 ) × 2
]

YxvYCC( N ) = round (219 × Y ′ + 16 ) × 2 n −8
Cb xvYCC( N )
CrxvYCC( N )

n −8

(7)

n −8

NOTE Bit levels “from 0 to 2 N-8 -1” and “from 254 x 2 N-8 + 1 to 2 N -1” (0 and 255, in the case of 8-bit encoding) are
used exclusively for synchronization and are not allowed for storing colour values. Levels from “2 N-8 ” to “254 x 2 N-8 ”
(from 1 to 254, in the case of 8-bit encoding) are available.


EN 61966-2-4:2006

–9–

5
5.1

Encoding transformations
Introduction

The encoding transformations between xvYCC values and CIE 1931 XYZ values provide
unambiguous methods to represent optimum image colorimetry of the captured scene. Scene
colorimetry is defined as relative to the white objects, assuming that the exposure is properly
controlled. It should be noted that dynamic range compression is needed when storing the
wide dynamic range images (see Annex A for descriptions). Additionally, if the condition of the
capturing device deviates from the ideal condition defined in Clause 4, operations such as
colour compensation, colour correction and a certain degree of colour rendering can be
performed. However, the methods for these operations are beyond the scope of this standard.
5.2

Transformation from xvYCC values to CIE 1931 XYZ values

For 24-bit encoding (8-bit/channel), the relationship between 8-bit values and Y ′, Cb ′, Cr ′ is
defined as:

(
)
Cb ′ = (Cb xvYCC(8 ) − 128 ) 224
Cr ′ = (CrxvYCC( 8) − 128 ) 224
Y ′ = YxvYCC(8 ) − 16 219

For N-bit/channel ( N > 8 ) encoding, the relationship between N-bit values and
defined as:

(8)

Y ′, Cb ′, Cr ′ is


 YxvYCC( N )
Y′ = 
− 16  219


N −8

 2

 Cb xvYCC( N )
Cb ′ = 
− 128  224


2 N −8



 CrxvYCC( N )
Cr ′ = 
− 128  224
N −8
2



For xvYCC 601 encoding, the non-linear

(9)

Y ′, Cb ′, Cr ′ values are transformed to the non-linear

R ′, G ′, B ′ values as follows:
 R ′  1,000 0
 ′ 
G  = 1,000 0
 B ′  1,000 0

0 ,000 0
− 0 ,344 1
1,772 0

′ 
1,402 0   Y601

 ′ 
− 0 ,714 1  Cb601 
′ 
0 ,000 0   Cr601

(10)

NOTE The possible range for non-linear R’G’B’ (601) calculated from, for example, equation (10) will be between
-1,0732 and 2,0835.

For xvYCC 709 encoding, the non-linear

Y ′, Cb ′, Cr ′ values are transformed to the non-linear

R ′, G ′, B ′ values as follows:
 R ′  1,000 0
 ′ 
G  = 1,000 0
 B ′  1,000 0

0 ,000 0
− 0 ,187 3
1,855 6

′ 
1,574 8   Y709
 ′ 
− 0 ,468 1  Cb709 
′ 
0 ,000 0   Cr709

(11)

NOTE The possible range for non-linear R’G’B’ (709) calculated from, for example, equation (11) will be between
-1,1206 and 2,1305.


EN 61966-2-4:2006
The non-linear

– 10 –

R ′, G ′, B ′ values are then transformed to linear R, G, B values as follows.

If R ′, G ′, B ′ < −0 ,081
1

 R ′ − 0,099  0,45
R = −

 − 1,099 
1

 G ′ − 0,099  0,45
G = −

 − 1,099 

(12)

1

 B ′ − 0,099  0,45
B = −

 − 1,099 
If −0 ,081 ≤ R ′, G ′, B ′ ≤ 0 ,081 ,
R = R ′ 4,50
G = G ′ 4,50
B = B ′ 4,50

(13)

If R ′, G ′, B ′ > 0 ,081 ,
1

 R ′ + 0,099  0,45
R=

 1,099 
1

 G ′ + 0,099  0,45
G=

 1,099 

(14)

1

 B ′ + 0,099  0,45
B=

 1,099 
The linear R, G , B values are transformed to CIE 1931 XYZ values as follows:
 X  0 ,412 4
  
 Y  = 0 ,212 6
 Z   0 ,019 3

0 ,357 6
0 ,715 2
0 ,119 2

0 ,180 5   R 
 
0 ,072 2  G 
0 ,950 5   B 

(15)

NOTE When the capturing device performs dynamic range compression of the brighter-than-white (for example,
specular) components, the compressed colours will be displayed at the top-end range of the "reference" display as
described in Annex C. In this case, the XYZ tristimulus values of the compressed components represent the
colorimetry of the rendered scene, not the colorimetry of the original scene.


EN 61966-2-4:2006

– 11 –

5.3

Transformation from CIE 1931 XYZ values to xvYCC values

The CIE 1931 XYZ values can be transformed to linear R, G , B values as follows:
 R   3 ,241 0
  
G  = − 0 ,969 2
 B   0 ,055 6

− 1,537 4
1,876 0
− 0 ,204 0

− 0 ,498 6   X 
 
0 ,041 6   Y 
1,057 0   Z 

(16)

In the xvYCC encoding process, negative RGB tristimulus values and RGB tristimulus values
greater than 1,0 are retained.
The linear R, G , B values are then transformed to non-linear R ′, G ′, B ′ values as follows.
If R, G, B ≤ −0 ,018 ,
R ′ = −1,099 × (− R )0,45 + 0,099
G ′ = −1,099 × (− G )0,45 + 0,099
B ′ = −1,099 × (− B )

0,45

(17)

+ 0,099

If −0 ,018 < R, G, B < 0 ,018 ,

R ′ = 4,50 × R
G ′ = 4,50 × G

(18)

B ′ = 4,50 × B
If R, G , B ≥ 0 ,018 ,
R ′ = 1,099 × (R )0,45 − 0,099
G ′ = 1,099 × (G )0,45 − 0,099

(19)

B ′ = 1,099 × (B )0,45 − 0,099

The relationship between non-linear R ′, G ′, B ′ and xvYCC 601 is defined as follows:
′   0 ,299 0
 Y601
 ′  
Cb601  = − 0 ,168 7
 Cr601
′   0 ,500 0

0 ,587 0
− 0 ,331 3
− 0 ,418 7

0 ,114 0   R ′
 
0 ,500 0  G ′
− 0 ,081 3   B ′

(20)

The relationship between non-linear R ′, G ′, B ′ and xvYCC 709 is defined as follows:
′   0 ,212 6
 Y709
 ′  
Cb709  = − 0 ,114 6
 Cr709
′   0 ,500 0

0 ,715 2
− 0 ,385 4
− 0 ,454 2

0 ,072 2   R ′
 
0 ,500 0  G ′
− 0 ,045 8   B ′

(21)

NOTE If the capturing device is capable of storing Y’ greater than 238/219 (or 1,086 758), dynamic range
compression can be performed at this stage. Please refer to Annex A for the descriptions.

and quantization for xvYCC for 24-bit encoding (8-bit/channel) is defined as:


EN 61966-2-4:2006

– 12 –
YxvYCC(8 ) = round[219 × Y ′ + 16]

Cb xvYCC(8 ) = round[224 × Cb ′ + 128]

(22)

CrxvYCC(8 ) = round[224 × Cr ′ + 128 ]

For 24-bit encoding, the xvYCC values shall be limited to a range from 1 to 254 according to
equation (22).
For N -bit/channel ( N > 8 ) encoding, the relationship is defined as:

[
]
= round[(224 × Cb ′ + 128 ) × 2
]
= round[(224 × Cr ′ + 128 ) × 2
]

YxvYCC( N ) = round (219 × Y ′ + 16 ) × 2 n −8

Cb xvYCC( N )
CrxvYCC( N )

n −8

(23)

n −8

For N -bit/channel encoding, the xvYCC values shall be limited to a range from “2
N-8
2 ” according to equation (23).

N-8

” to “254 ×


EN 61966-2-4:2006

– 13 –

Annex A
(informative)
Compression of specular components of Y’ signals

This annex describes an example method for the dynamic range compression of the
components that are brighter than white in Y ′ (or Luma) signal, such as specular highlights.
In xvYCC colour encoding, linear R, G , B values according to equation (16), or non-linear

R ′, G ′, B ′ values according to equations (17) to (19) are not limited between 0 and 1. After
the YCC quantization (equation (22)), the value range will be limited as follows:
Y ′ signal:
Cb ′, Cr ′ signal:

-15/219 to +238/219 (or -0,068 493 to +1,086 758)
-15/224 to +238/224 (or -0,066 964 to +1,062 500)

For the surface colours, Y ′ signals shall be in the range of 0 and 1, while over-ranged values
(greater than 1,0 or smaller than 0,0) in Cb ′ and Cr ′ are used for storing saturated colours.
However, if the specular components that are brighter than white exist in a captured image,
there will be pixels with Y ′ signals greater than “1”. These components must be compressed
(or clipped) into the given quantization range. An example of the specular compression
method is provided in Figure A.1.
NOTE Different proprietary compression methods in either Y’ components or R’G’B’ components are used in
practice.

256
235

YxvYCC(8)

192

128

64
16
0
0

0,5

1

1,5
Y'

2

2,5

3
IEC 2665/05

Figure A.1 – Example of the specular compression method


EN 61966-2-4:2006

– 14 –

Annex B
(informative)
Default transformation from 16-bit scRGB values to xvYCC values

B.1

Introduction

This annex describes the default transformation from scRGB (as defined in IEC 61966-2-2) to
xvYCC. Since the dynamic range of scRGB is wider than that of xvYCC, dynamic range
compression (or clipping) for brighter than white colours is needed in the transformation (see
Annex A for details).

B.2

Transformation from scRGB values to 8-bit xvYCC

The relationship between 16-bit scRGB values and linear

RscRGB , GscRGB , BscRGB values is

defined as follows:

(
= (G
= (B

)
) ÷ 8 192,0 ) − 0,5
) ÷ 8 192,0 ) − 0,5

RscRGB = RscRGB(16 ) ÷ 8 192,0 − 0,5

GscRGB
BscRGB
The linear

scRGB(16

scRGB(16

(B.1)

RscRGB , GscRGB , BscRGB values are then transformed to non-linear R′, G ′, B′ values as

follows.
If

RscRGB , GscRGB , BscRGB < −0,018
R ′ = −1,099 × (− RscRGB )0,45 + 0,099
G ′ = −1,099 × (− GscRGB )0,45 + 0,099

(B.2)

B ′ = −1,099 × (− BscRGB )0,45 + 0,099
If − 0 ,018 ≤ RscRGB , GscRGB , BscRGB ≤ 0 ,018 ,
R ′ = 4,50 × RscRGB
G ′ = 4,50 × G scRGB
B ′ = 4,50 × BscRGB

(B.3)

If RscRGB , GscRGB , BscRGB > 0 ,018 ,
R ′ = 1,099 × (RscRGB )0,45 − 0,099
G ′ = 1,099 × (G scRGB )0,45 − 0,099
B ′ = 1,099 × (BscRGB )

0,45

− 0,099

(B.4)


EN 61966-2-4:2006

– 15 –

The relationship between non-linear R ′, G ′, B ′ and xvYCC 601 is defined as follows:
′   0 ,299 0
 Y601
 ′  
Cb601  = − 0 ,168 7
 Cr601
′   0 ,500 0

0 ,587 0
− 0 ,331 3
− 0 ,418 7

0 ,114 0   R ′
 
0 ,500 0  G ′
− 0 ,081 3   B ′

(B.5)

The relationship between non-linear R ′, G ′, B ′ and xvYCC 709 is defined as follows:

′   0,212 6
 Y709
 ′  
C
b
 709  = − 0 ,114 6
 Cr709
′   0 ,500 0

0,715 2
− 0 ,385 4
− 0 ,454 2

0 ,072 2   R ′
 
0 ,500 0  G ′
− 0 ,045 8   B ′

(B.6)

NOTE If the capturing device is capable of storing Y’ greater than 238/219 (or 1,086 758), dynamic range
compression can be performed at this stage. See Annex A for the descriptions.

and quantization for xvYCC for 24-bit encoding (8-bit/channel) is defined as:
YxvYCC(8 ) = round[219 × Y ′ + 16]

Cb xvYCC(8 ) = round[224 × Cb ′ + 128]

(B.7)

CrxvYCC(8 ) = round[224 × Cr ′ + 128 ]

For 24-bit encoding, the xvYCC values shall be limited to a range from 1 to 254 according to
equation (22).
For N-bit/channel ( N > 8 ) encoding, the relationship is defined as:

[
]
= round[(224 × Cb ′ + 128 ) × 2
]
= round[(224 × Cr ′ + 128 ) × 2
]

YxvYCC( N ) = round (219 × Y ′ + 16 ) × 2 n −8
Cb xvYCC( N )
CrxvYCC( N )

n −8

(B.7’)

n −8

For N-bit/channel encoding, the xvYCC values shall be limited to a range from “2
N-8
2 ” according to equation (23).

N-8

” to “254 ×

EN 61966-2-4:2006

– 16 –

Annex C
(informative)
xvYCC/ITU-R BT.709 and sYCC/sRGB compatibility

Annex B of IEC 61966-2-1 provides an explanation for the compatibility between sRGB and
ITU-R BT.709. ITU-R BT.709 specifically describes the encoding of the “reference” video
camera, which will produce an “excellent” image when the resulting image is viewed on a
“reference” display. IEC 61966-2-1 provides a clear and well-defined “reference” display for a
dim viewing environment.
Figure C.1 illustrates both the sRGB colour space and the extraction of the reference display
specifications (with its viewing conditions) implicit in ITU-R BT.709. By building on this system,
the sRGB colour space provides a display definition that can be used independently from ITUR BT.709 while maintaining compatibility. The tree, first arrow, camera, second arrow and
circled display represent the same concepts as in Figure C.1. The bottom display is identical
to the targeted ITU display and is intended to show that sRGB is simply the targeted display
of the ITU capture/display system, independent of the capture encoding space.

ITU-R BT.709

sRGB
IEC 2666/05

Figure C.1 – Relationship between ITU-R BT.709 and sRGB

However, this system was based on the CRT displays whose RGB chromaticity is within a

certain tolerance of the sRGB specification. With the emergence of novel displays based on
other technologies (for example, LCDs, PDPs, etc.) that are capable of displaying wider
colour gamut, the demands for extended-gamut colour space encoding increased. IEC 619662-1, Amendment 1, was published to answer those needs for storing and exchanging out-ofsRGB-gamut saturated colours between devices. This sYCC colour space is adopted in the
Exif file format (JEITA CP-3451) and is now in widespread use in still imaging applications.
On the other hand, ITU-R BT.709 colour space is utilized for storing and exchanging in most
of the video applications. Therefore, this standard is intended to provide a solution for
extending the gamut of ITU-R BT.709, like sYCC colour space extended the gamut of sRGB
colour space.
Figure C.2 illustrates the same flow as Figure C.1, but ITU-R BT.709 is now replaced by
extended-gamut colour space: xvYCC, and sRGB is replaced by sYCC.


EN 61966-2-4:2006

– 17 –

ITU-RxvYCC
BT.709-3

sYCC

sRGB
IEC

2667/05

Figure C.2 – Relationship between xvYCC and sYCC


EN 61966-2-4:2006

– 18 –

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___________