IEC 61966-2-2:2003

IEC 61966-2-2
Edition 1.0 2003-01
INTERNATIONAL
STANDARD
Multimedia systems and equipment – Colour measurement and management –
Part 2-2: Colour management – Extended RGB colour space – scRGB

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IEC 61966-2-2
Edition 1.0 2003-01
INTERNATIONAL
STANDARD
Multimedia systems and equipment – Colour measurement and management –

Part 2-2: Colour management – Extended RGB colour space – scRGB

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.160.60; 37.080 ISBN 978-2-8322-0631-7

– 2 – 61966-2-2  IEC:2003(E)
CONTENTS
FOREWORD . 3
INTRODUCTION .5
1 Scope . 6
2 Normative references. 6
3 Definitions. 6
4 Encoding characteristics . 7
4.1 General . 7
4.2 Transformation from CIE 1931 XYZ values to 16-bit scRGB values
( R , G , B ) . 7
scRGB scRGB scRGB
()16 (16) ()16
4.3 Transformation from 16-bit scRGB values
( R , G , B ) to CIE 1931 XYZ values. 7
scRGB scRGB scRGB
()16 (16) ()16
Annex A (informative) Simple transformation between 8-bit sRGB and 16-bit scRGB
values . 8
Annex B (informative) Non-linear encoding for scRGB: scRGB-nl and its YCC
Transformation: scYCC-nl.10
Annex C (informative) scRGB background information .12
Bibliography .16
Figure C.1 – Example workflow using scRGB.15
Table B.1 – Quantization relationships using scRGB .11

61966-2-2  IEC:2003(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MULTIMEDIA SYSTEMS AND EQUIPMENT –
COLOUR MEASUREMENT AND MANAGEMENT –
Part 2-2: Colour management –
Extended RGB colour space – scRGB
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
The International Electrotechnical Commission (IEC) draws attention to the fact that it is claimed that compliance
with this document may involve the use of a patent concerning encoding of colour management given in Clause 4.
The IEC takes no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured the IEC that he is willing to negotiate licences under reasonable and
non-discriminatory terms and conditions with applicants throughout the world. In this respect, the statement of the
holder of this patent right is registered with IEC. Information may be obtained from:
Eastman Kodak Company
343 State Street
Rochester
New York 14650
USA
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights
other than those identified above. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61966 has been prepared by Technical Area 2: Colour
measurement and management, of IEC technical committee 100: Audio, video and multimedia
systems and equipment and ISO TC 42: Photography.
The text of this standard is based on the following documents:
FDIS Report on voting
100/556A/FDIS 100/626/RVD
– 4 – 61966-2-2  IEC:2003(E)
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 61966 consists of the following parts, under the general title Multimedia systems and
equipment – Colour measurement and management:
Part 2-1: Colour management – Default RGB colour space – sRGB
Part 2-2: Colour management – Extended RGB colour space – scRGB
Part 3: Equipment using cathode ray tubes
Part 4: Equipment using liquid crystal display panels
Part 5: Equipment using plasma display panels
Part 7-1. Colour printers – Reflective prints – RGB inputs
Part 8: Multimedia colour scanners
Part 9: Digital cameras
It is published as a double logo standard.
In the ISO the Standard has been approved by 9 P-members out of 10 having cast the vote.
The committee has decided that the contents of this publication will remain unchanged until 2007.
At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of August 2003 have been included in this copy.

61966-2-2  IEC:2003(E) – 5 –
INTRODUCTION
The IEC 61966 standards are a series of methods and parameters for colour measurements
and management for use in multimedia systems and equipment applicable to the assessment
of colour reproduction.
The method of digitization in this part is designed to provide high bit precision, large colour
gamut and extended dynamic range that is linear with respect to scene radiance. Based on
IEC 61966-2-1 (sRGB), this colour space is well suited to meet the needs of the multimedia,
gaming and computer graphics applications. This standard provides a robust solution to these
needs. The white point and colour primaries of the scRGB solution are directly inherited from
the IEC 61966-2-1 (sRGB) standard. The encoding transformations provide all of the necessary
information to encode an image.

– 6 – 61966-2-2  IEC:2003(E)
MULTIMEDIA SYSTEMS AND EQUIPMENT –
COLOUR MEASUREMENT AND MANAGEMENT –
Part 2-2: Colour management –
Extended RGB colour space – scRGB
1 Scope
This part of IEC 61966 is applicable to the encoding, editing and communication of relative
scene radiance, wide dynamic range, extended colour gamut, and extended bit precision RGB
colours as a colour space used in computer systems and similar applications by defining
encoding transformations. Primaries and white point values of the colour space defined in this
standard are identical to CIE chromaticities for ITU-R BT.709-5 reference primaries and CIE
standard illuminant D65 as its white point. The scRGB colour space is an extension of sRGB
and it is considered compatible with sRGB.
Additional transformations, such as white point adaptation methods, are beyond the scope of
this standard. The appropriate CIE recommendations should be referred to for guidelines
in this area.
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) – Chapter 845: Lighting
3 Definitions
For the purposes of this document, the following definitions apply. Definitions of illuminance,
radiance, tristimulus, and other relating lighting terms are defined in IEC 60050(845).
3.1
output referred colour space
a colour space that represents the colorimetry of an output device with specified viewing
conditions
3.2
wide dynamic range colour space
a colour space whose encoding encompasses values below black and above white
3.3
luma
luminance signal as defined by SMPTE/EG28: 1993
NOTE Video systems approximate the lightness response of vision by computing a luma component Y′ as a
weighted sum of nonlinear R′G′B′ primary components: Each RGB signal is, comparable to the 1/3 power function
with an offset defined by L*. Luma is often incorrectly referred to as luminance.

61966-2-2  IEC:2003(E) – 7 –
4 Encoding characteristics
4.1 General
The encoding transformations provide unambiguous methods to transform between CIE 1931
XYZ tristimulus values and 16-bit values for each channel of scRGB. The CIE 1931 XYZ
values are scaled so that the sRGB black point to white point luminance is 0,0 to 1,0, not 0,0
to 100,0. Y-tristimulus values less than 0,0 in CIE 1931 XYZ space represent values below
black. Y-tristimulus values greater than 1,0 represent values brighter than relative white.
The scRGB components that range from 0 to 16 384 encompass all visible surface colours
(from −0,5 to 1,5). The range from 12 288 to 65 535 is used to encode an extended specular
range of colours (from larger than 1,0 to 7,4999).
4.2 Transformation from CIE 1931 XYZ values to 16-bit scRGB values
( R , G , B )
scRGB scRGB scRGB
()16 (16) ()16
The relationship is defined as follows:
R 3,240625 −1,537 208 − 0,498629 X
    
scRGB
    
G = − 0,968931 1,875756 0,041518 Y (1)
scRGB
    
    
B 0,055710 − 0,204021 1,056996 Z
 scRGB
  
R = round[]()R × 8192,0 + 4 096
scRGB scRGB
()16
and: G = round[]()G × 8192,0 + 4 096 (2)
scRGB scRGB
()16
B = round[]()B × 8192,0 + 4 096
scRGB scRGB
()16
4.3 Transformation from 16-bit scRGB values ( R , G , B )
scRGB scRGB scRGB
()16 (16) ()16
to CIE 1931 XYZ values
The relationship is defined as follows:
R = (R ÷ 8192,0)− 0,5
scRGB scRGB
()16
G =()G ÷ 8192,0 − 0,5 (3)
scRGB scRGB
()16
B =()B ÷ 8192,0 − 0,5
scRGB scRGB
()16
X 0,412 4 0,357 6 0,180 5 R
    
scRGB
    
and Y = 0,212 6 0,715 2 0,072 2 G
...