Photography and graphic technology — Extended colour encodings for digital image storage, manipulation and interchange — Part 3: Reference input medium metric RGB colour image encoding (RIMM RGB)

This document specifies a family of scene-referred extended colour gamut RGB colour image encodings designated as reference input medium metric RGB (RIMM RGB). Digital images encoded using RIMM RGB can be manipulated, stored, transmitted, displayed or printed by digital still picture imaging systems. Three precision levels are defined using 8-, 12- and 16-bits/channel. An extended luminance dynamic range version of RIMM RGB is also defined, designated as extended reference input medium metric RGB (ERIMM RGB). Two precision levels of ERIMM RGB are defined using 12- and 16-bits/channel. FP-RIMM RGB, a floating point version of RIMM RGB, defines the expression method of RIMM RGB in a floating point figure. Three precision levels of FP-RIMM RGB are defined using 16-, 32- and 64-bits/channel.

Photographie et technologie graphique — Codages par couleurs étendues pour stockage, manipulation et échange d'image numérique — Partie 3: Codage d'image en couleurs RVB par référence d'entrée par voie métrique

General Information

Status
Published
Publication Date
05-Jan-2023
Technical Committee
Drafting Committee
Current Stage
6060 - International Standard published
Due Date
09-Aug-2024
Completion Date
06-Jan-2023
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INTERNATIONAL ISO
STANDARD 22028-3
First edition
2023-01
Photography and graphic
technology — Extended colour
encodings for digital image storage,
manipulation and interchange —
Part 3:
Reference input medium metric RGB
colour image encoding (RIMM RGB)
Photographie et technologie graphique — Codages par couleurs
étendues pour stockage, manipulation et échange d'image
numérique —
Partie 3: Codage d'image en couleurs RVB par référence d'entrée par
voie métrique
Reference number
ISO 22028-3:2023(E)
© ISO 2023
---------------------- Page: 1 ----------------------
ISO 22028-3:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023

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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2023 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 22028-3:2023(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Requirements .......................................................................................................................................................................................................... 5

4.1 General ........................................................................................................................................................................................................... 5

4.2 Adopted white ......................................................................................................................................................................................... 7

4.3 Reference medium primaries and white point .......................................................................................................... 7

4.4 RIMM RGB, ERIMM RGB, FP-RIMM RGB colour image encoding ............................................................... 7

4.4.1 Encoding principles ......................................................................................................................................................... 7

4.4.2 Tristimulus value normalization ......................................................................................................................... 8

4.4.3 RIMM RGB conversion matrix ................................................................................................................................ 8

4.4.4 RIMM RGB colour component transfer function .................................................................................... 9

4.4.5 RIMM RGB digital encoding function ............................................................................................................... 9

4.4.6 ERIMM RGB colour component transfer function ................................................................................ 9

4.4.7 ERIMM RGB digital encoding function ........................................................................................................ 10

4.4.8 FP-RIMM RGB colour component transfer function ........................................................................ 11

4.5 Inverse RIMM RGB transformation ................................................................................................................................... 11

4.5.1 General ..................................................................................................................................................................................... 11

4.5.2 Inverse RIMM RGB digital encoding function ....................................................................................... 11

4.5.3 Inverse RIMM RGB colour component transfer function ............................................................12

4.5.4 Inverse ERIMM RGB digital encoding function ....................................................................................12

4.5.5 Inverse ERIMM RGB colour component transfer function .........................................................13

4.5.6 Inverse RIMM RGB conversion matrix ......................................................................................................... 13

4.5.7 Inverse tristimulus value normalization ...................................................................................................13

4.5.8 Inverse FP-RIMM RGB colour component transfer function .................................................... 14

Annex A (informative) Example colour rendering transform from RIMM RGB to ROMM RGB ..........15

Annex B (informative) Cultural heritage applications of RIMM RGB.............................................................................20

Bibliography .............................................................................................................................................................................................................................24

iii
© ISO 2023 – All rights reserved
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ISO 22028-3:2023(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

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 ISO documents 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 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 of 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

www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 42, Photography.

This first edition of ISO 22028-3:2022 cancels and replaces the second edition (ISO/TS 22028-3:2012),

which has been technically revised.
The main changes are as follows:
— the Kodak IP statement has been removed;
— some references have been added, deleted, or updated;
— Annex B has been added.
A list of all parts in the ISO 22028 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2023 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 22028-3:2023(E)
Introduction

This document has been developed in order to meet the industry need for a complete, fully-documented,

publicly-available definition of a wide-primary scene-referred extended colour gamut red-green-blue

(RGB) colour image encoding. This encoding provides a way to represent scene-referred images that

does not limit the colour gamut to those colours capable of being displayed on a CRT monitor or require

the use of negative RGB colourimetry coordinates.

A scene-referred extended colour gamut colour encoding is particularly desirable for professional

photography and cultural heritage applications. For example, colours captured by digital cameras,

as well as conventional capture devices such as photographic film, can be outside those that can be

represented within the colour gamut of a typical monitor or other types of output devices. Similarly,

scene-referred images can have a larger luminance dynamic range than output-referred images since

they have not been modified by a colour rendering process to fit the images to a specific output medium

applying appropriate tone and colour reproduction aims. Retaining the unrendered scene-referred

image data has the advantage that it preserves the option to make decisions about how a particular

image is to be rendered. For example, a scene-referred image of a backlit scene can retain information

about both the dark foreground region and the bright background region of the scene. This information

can be used to make a properly exposed print of either the foreground region or the background region,

or alternatively can be used to create an improved image by rendering the two regions differently.

By using a standard scene-referred extended colour gamut colour image encoding, images can be

stored, interchanged and manipulated without restricting the image to a particular rendering intent

or output device. The reference input medium metric RGB (RIMM RGB) colour encoding specified in

this document meets the needs of these types of applications, as described in References [14] and

[15]. An extended dynamic range version of this colour image encoding known as extended reference

input medium metric RGB (ERIMM RGB), and a floating point version known as FP-RIMM RGB are also

specified for use with high-dynamic range input sources. The scene-referred RIMM RGB colour image

encoding is intended to be complementary to the output-referred ROMM RGB colour image encoding

[10]

specified in ISO 22028-2 . Both colour encodings are based on the same “wide RGB” additive colour

space to facilitate the development of image processing algorithms and simple colour rendering

transformations to convert scene-referred RIMM RGB images to rendered output-referred ROMM RGB

images.
© ISO 2023 – All rights reserved
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 22028-3:2023(E)
Photography and graphic technology — Extended colour
encodings for digital image storage, manipulation and
interchange —
Part 3:
Reference input medium metric RGB colour image
encoding (RIMM RGB)
1 Scope

This document specifies a family of scene-referred extended colour gamut RGB colour image encodings

designated as reference input medium metric RGB (RIMM RGB). Digital images encoded using RIMM RGB

can be manipulated, stored, transmitted, displayed or printed by digital still picture imaging systems.

Three precision levels are defined using 8-, 12- and 16-bits/channel.

An extended luminance dynamic range version of RIMM RGB is also defined, designated as extended

reference input medium metric RGB (ERIMM RGB). Two precision levels of ERIMM RGB are defined

using 12- and 16-bits/channel.

FP-RIMM RGB, a floating point version of RIMM RGB, defines the expression method of RIMM RGB in

a floating point figure. Three precision levels of FP-RIMM RGB are defined using 16-, 32- and 64-bits/

channel.
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.

ISO/CIE 11664-1, Colorimetry — Part 1: CIE standard colorimetric observers
CIE Publication 15, Colorimetry
IEEE 754, IEEE Standard for Floating-Point Arithmetic
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
1) This International Standard replaces ISO/CIE 10527.
© ISO 2023 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 22028-3:2023(E)
3.1
adapted white

colour stimulus that an observer who is adapted to the viewing environment would judge to be perfectly

achromatic and to have a luminance factor of unity; i.e. absolute colourimetric coordinates that an

observer would consider to be a perfect white diffuser
Note 1 to entry: The adapted white can vary within a scene.
3.2
additive RGB colour space

colourimetric colour space having three colour primaries (generally red, green and blue) such that

CIE XYZ tristimulus values can be determined from the RGB colour space values by forming a weighted

combination of the CIE XYZ tristimulus values for the individual colour primaries, where the weights are

proportional to the radiometrically linear colour space values for the corresponding colour primaries

Note 1 to entry: A simple linear 3 × 3 matrix transformation can be used to transform between CIE XYZ

tristimulus values and the radiometrically linear colour space values for an additive RGB colour space.

Note 2 to entry: Additive RGB colour spaces are defined by specifying the CIE chromaticity values for a set of

additive RGB primaries and a colour space white point, together with a colour component transfer function.

3.3
adopted white

spectral radiance distribution as seen by an image capture or measurement device and converted

to colour signals that are considered to be perfectly achromatic and to have an observer adaptive

luminance factor of unity; i.e. colour signals that are considered to correspond to a perfect white

diffuser

Note 1 to entry: The adopted white can vary within a scene, if such variation is supported by the imaging system.

Note 2 to entry: The adopted white is not required to be an estimate or approximation of the adapted white.

For example, if a scene lit by tungsten illumination is captured using a DSC with the white balance set to D55

(daylight), the adopted white will be D55 but the adapted white will be closer to a tungsten illuminant (e.g.

[1]
ISO 7589 Studio Tungsten or CIE Illuminant A).

Note 3 to entry: The adopted white can be equal to the adapted white in certain situations and can be different

than the adapted white in other situations. See 3.1.
3.4
colourimetric colour space
colour space having an exact and simple relationship to CIE colourimetric values

Note 1 to entry: Colourimetric colour spaces include those defined by CIE (e.g. CIE XYZ, CIELAB, CIELUV), as well

as colour spaces that are simple transformations of those colour spaces (e.g. additive RGB colour spaces (3.2)).

3.5
colour component transfer function

single variable, monotonic mathematical function applied individually to one or more colour channels

of a colour space (3.10)

Note 1 to entry: Colour component transfer functions are frequently used to account for the nonlinear response

of a reference device and/or to improve the visual uniformity of a colour space.

Note 2 to entry: Generally, colour component transfer functions will be nonlinear functions such as a power-law

(i.e. “gamma”) function or a logarithmic function. However, in some cases a linear colour component transfer

function can be used.
3.6
colour encoding

generic term for a quantized digital encoding of a colour space (3.10), encompassing both colour space

encodings (3.11) and colour image encodings (3.8)
© ISO 2023 – All rights reserved
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ISO 22028-3:2023(E)
3.7
colour gamut

solid in a colour space (3.10), consisting of all those colours that are either present in a specific scene,

artwork, photograph, photomechanical, or other reproduction, or capable of being created using a

particular output device and/or medium
3.8
colour image encoding

digital encoding of the colour values for a digital image, including the specification of a colour space

encoding (3.11), together with any information necessary to properly interpret the colour values such

as the image state, the intended image viewing environment and the reference medium

Note 1 to entry: In some cases, the intended image viewing environment will be explicitly defined for the colour

image encoding. In other cases, the intended image viewing environment can be specified on an image-by-image

basis using metadata associated with the digital image.

Note 2 to entry: Some colour image encodings will indicate particular reference medium characteristics, such as

a reflection print with a specified density range. In other cases, the reference medium will not be applicable, such

as with a scene-referred colour image encoding, or will be specified using image metadata.

Note 3 to entry: Colour image encodings are not limited to pictorial digital images that originate from an original

scene, but are also applicable to digital images with content such as text, line art, vector graphics and other forms

of original artwork.
3.9
colour rendering

mapping of image data representing the colour-space coordinates of the elements of a scene to output-

referred image data representing the colour space (3.10) coordinates of the elements of a reproduction

Note 1 to entry: Colour rendering generally consists of one or more of the following:

— compensating for differences in the input and output viewing conditions;

— tone scale and gamut mapping to map the scene colours onto the dynamic range and colour gamut (3.7) of the

reproduction;
— applying preference adjustments.
3.10
colour space
geometric representation of colours in space, usually of three dimensions
[SOURCE: CIE Publication 17.4:1987, 845-03-25]
3.11
colour space encoding

digital encoding of a colour space (3.10), including the specification of a digital encoding method, and a

colour space (3.10) value range

Note 1 to entry: Multiple colour space encodings can be defined based on a single colour space where the different

colour space encodings have different digital encoding methods and/or colour space value ranges. (For example,

8-bit sRGB and 10-bit e-sRGB are different colour space encodings based on a particular RGB colour space.)

3.12
colour space white point
colour stimulus to which colour space (3.10) values are normalized

Note 1 to entry: It is not necessary that the colour space white point correspond to the assumed adapted white

point and/or the reference medium white point for a colour image encoding (3.8).
© ISO 2023 – All rights reserved
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ISO 22028-3:2023(E)
3.13
image state

attribute of a colour image encoding (3.8) indicating the rendering state of the image data

Note 1 to entry: The primary image states defined in this document are the scene-referred image state, the

original-referred image state and the output-referred image state.
3.14
luminance factor

ratio of the luminance of the surface element in the given direction to that of a perfect reflecting or

transmitting diffuser identically illuminated
[SOURCE: CIE Publication 17.4:1987, 845-04-69]
3.15
observer adaptive luminance factor

ratio of the luminance of a stimulus to the luminance of a stimulus that an observer adapted to the

viewing environment would interpret to be a perfect white diffuser
3.16
output-referred image state

image state (3.13) associated with image data that represents the colour space (3.10) coordinates of

the elements of an image that has undergone colour rendering (3.9) appropriate for a specified real or

virtual output device and viewing conditions

Note 1 to entry: When the phrase “output-referred” is used as a qualifier to an object, it implies that the object is

in an output-referred image state. For example, output-referred image data are image data in an output-referred

image state.

Note 2 to entry: Output referred image data are referred to the specified output device and viewing conditions. A

single scene can be colour rendered to a variety of output-referred representations depending on the anticipated

output viewing conditions, media limitations and/or artistic intents.

Note 3 to entry: Output-referred image data can become the starting point for a subsequent reproduction process.

For example, sRGB output-referred image data are frequently considered to be the starting point for the colour

re-rendering performed by a printer designed to receive sRGB image data.
3.17
scene

spectral radiances of a view of the natural world as measured from a specified vantage point in space

and at a specified time

Note 1 to entry: A scene can correspond to an actual view of the natural world or to a computer-generated virtual

scene simulating such a view.
3.18
scene-referred image state

image state (3.13) associated with image data that represents estimates of the colour space (3.10)

coordinates of the elements of a scene

Note 1 to entry: When the phrase “scene-referred” is used as a qualifier to an object, it implies that the object is

in a scene-referred image state. For example, scene-referred image data are image data in a scene-referred image

state.

Note 2 to entry: Scene-referred image data can be determined from raw DSC image data before colour rendering

(3.9) is performed. Generally, DSCs do not write scene-referred image data in image files, but some do so in a

special mode intended for this purpose. Typically, DSCs write standard output-referred image data where colour

rendering has already been performed.

Note 3 to entry: Scene-referred image data typically represents relative scene colourimetry estimates.

Absolute scene colourimetry estimates can be calculated using a scaling factor. The scaling factor can be

derived from additional information such as the image OECF, FNumber or ApertureValue, and ExposureTime or

ShutterSpeedValue tags.
© ISO 2023 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 22028-3:2023(E)

Note 4 to entry: Scene-referred image data can contain inaccuracies due to the dynamic range limitations of the

capture device, noise from various sources, quantization, optical blurring and flare that are not corrected for,

and colour analysis errors due to capture device metamerism. In some cases, these sources of inaccuracy can be

significant.

Note 5 to entry: The transformation from raw DSC image data to scene-referred image data depends on the

relative adopted whites (3.3) selected for the scene and the colour space used to encode the image data. If the

chosen scene adopted white is inappropriate, additional errors will be introduced into the scene-referred image

data. These errors can be correctable if the transformation used to produce the scene-referred image data are

known, and the colour encoding (3.6) used for the incorrect scene-referred image data has adequate precision

and dynamic range.

Note 6 to entry: The scene can correspond to an actual view of the natural world, or be a computer-generated

virtual scene simulating such a view. It can also correspond to a modified scene determined by applying

modifications to an original scene to produce some different desired scene. Any such scene modifications need to

leave the image in a scene-referred image state and need to be done in the context of an expected colour rendering

(3.9) transform.
3.19
tristimulus value

amounts of the three reference colour stimuli, in a given trichromatic system, required to match the

colour of the stimulus considered
[SOURCE: CIE Publication 17.4:1987, 845-03-22]
3.20
veiling glare

light, reflected from an imaging medium, that has not been modulated by the means used to produce

the image

Note 1 to entry: Veiling glare lightens and reduces the contrast of the darker parts of an image.

[12]

Note 2 to entry: In CIE Publication 122 , the veiling glare of a CRT display is referred to as ambient flare.

3.21
viewing flare

veiling glare that is observed in a viewing environment but not accounted for in radiometric

measurements made using a prescribed measurement geometry

Note 1 to entry: The viewing flare is expressed as a percentage of the luminance of adapted white.

3.22
working colour space

colour space encoding (3.11) in which operations such as image edits, enhancements, or colour rendering

(3.9) are performed

Note 1 to entry: The image state in a working colour space can change as operations are performed.

Note 2 to entry: If operations performed in a working colour space are guided by viewing the image on a medium,

that medium and the associated viewing conditions become the reference for the resulting image.

4 Requirements
4.1 General

Reference input medium metric RGB (RIMM RGB) and the ERIMM and FP-RIMM associated versions

of RIMM RGB are extended colour gamut RGB colour image encodings of the colourimetry of a scene-

referred image, white balanced to be relative to a specified adopted white. The image colourimetry is

encoded in terms of an additive RGB colour space (i.e. a colourimetric colour space) associated with a

hypothetical additive colour device having a specified set of primaries and no cross-talk between the

colour channels. The RIMM RGB colour image encoding has a maximum luminance value corresponding

© ISO 2023 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 22028-3:2023(E)

to 200 % of a perfect diffuse reflector (i.e. an observer adaptive luminance factor of 2,0). Extended

reference input medium metric RGB (ERIMM RGB) is an extended luminance dynamic range version

of RIMM RGB having a maximum observer adaptive luminance factor of about 316. The maximum

luminance value of FP-RIMM RGB colour image encoding is limited only by the floating point encoding

range. In RIMM RGB, ERIMM RGB and FP-RIMM RGB, the image colourimetry shall be based on flareless

(or flare corrected) colourimetric measurements as described in CIE Publication 15 using the CIE 1931

standard colourimetric observer defined in ISO/CIE 11664-1.

Scene-referred image data may correspond to an actual view of the natural world, or a simulation of

such a view. It may also correspond to a modified scene determined by applying modifications to an

original scene. In order to be appropriate for encoding as RIMM RGB, ERIMM RGB or FP-RIMM RGB, any

scene modifications shall leave the image in a scene-referred image state.

Scene-referred image data may have an associated pre-determined colour rendering transform. When

an associated pre-determined colour rendering transform is present with scene-referred image data,

such an intended colour rendering transform should be included in any image preview path that is used

to provide subjective feedback to a user, unless

— the user has selected direct viewing of the scene-referred image and intends that modifications are

to be previewed in the scene-referred state, and

— the scene-referred image data has been converted to an appropriate working colour space for manual

editing and colour rendering. In this case the user may exercise the option to apply or not apply an

associated pre-determined colour rendering transform, if present, when the scene-referred image

data are converted to the working colour space.

EXAMPLES Scene modifications could include removing haze from the captured image or allowing a user

to manually adjust the exposure/white balance. It could also include more complex operations such as using a

“dodge-and-burn” algorithm to correct over-exposed regions of a backlit scene. (This can be viewed as being

analogous to “re-lighting” the scene.) Scene modifications could also include applying desired changes to the

scene such as simulating a “night” scene, making grass greener to make it look healthier, or making the sky bluer

to make it look clearer. However, typical colour rendering transforms will include a boost in the midtone contrast

and chroma of the image. Consequently, any boost in colourfulness of the scene (e.g. making the grass greener)

needs to be done with the knowledge that there
...

ISO 22028-3:2022(E)
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ISO TC 42/WG 23
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Date: 2022-10-27xx
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Photography and graphic technology — Extended colour encodings for digital image
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storage, manipulation and interchange — Part 3: Reference input medium metric RGB

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colour image encoding (RIMM RGB)
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Photographie et technologie graphique — Codages par couleurs étendues pour stockage, Style Definition: ANNEX

manipulation et échange d'image numérique — Partie 3: Codage d'image en couleurs RVB par

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référence d'entrée par voie métrique
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ISO 22028-3:2022(E)
© ISO 2022
Formatted: Pattern: Clear
Formatted: Pattern: Clear

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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
ii © ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 22028-3:2022(E)
Contents

Foreword ............................................................................................................................................................ iv

Introduction ....................................................................................................................................................... v

1 Scope ....................................................................................................................................................... 1

2 Normative references ....................................................................................................................... 1

3 Terms and definitions ....................................................................................................................... 1

4 Requirements ...................................................................................................................................... 5

4.1 General ................................................................................................................................................... 5

4.2 Adopted white ..................................................................................................................................... 6

4.3 Reference medium primaries and white point ......................................................................... 7

4.4 RIMM RGB, ERIMM RGB, FP-RIMM RGB colour image encoding .......................................... 7

4.4.1 Encoding principles ........................................................................................................................... 7

4.4.2 Tristimulus value normalization ................................................................................................... 8

4.4.3 RIMM RGB conversion matrix ........................................................................................................ 8

4.4.4 RIMM RGB colour component transfer function ...................................................................... 8

4.4.5 RIMM RGB digital encoding function ........................................................................................... 9

4.4.6 ERIMM RGB colour component transfer function .................................................................... 9

4.4.7 ERIMM RGB digital encoding function ......................................................................................... 9

4.4.8 FP-RIMM RGB colour component transfer function ............................................................. 10

4.5 Inverse RIMM RGB transformation............................................................................................ 10

4.5.1 General ................................................................................................................................................ 10

4.5.2 Inverse RIMM RGB digital encoding function ......................................................................... 11

4.5.3 Inverse RIMM RGB colour component transfer function .................................................... 11

4.5.4 Inverse ERIMM RGB digital encoding function ...................................................................... 11

4.5.5 Inverse ERIMM RGB colour component transfer function ................................................. 12

4.5.6 Inverse RIMM RGB conversion matrix ...................................................................................... 12

4.5.7 Inverse tristimulus value normalization ................................................................................. 12

4.5.8 Inverse FP-RIMM RGB colour component transfer function ............................................. 13

Annex A (informative) Example colour rendering transform from RIMM RGB to ROMM RGB

............................................................................................................................................................... 14

Annex B (informative) Cultural Heritage Applications of RIMM RGB .......................................... 19

B.1 General ...................................................................................................................................................... 19

B.2 Capturing RIMM images ....................................................................................................................... 19

B.3 Guidance for setting the white balance ........................................................................................... 20

B.4 Guidance for setting the proper exposure ..................................................................................... 20

B.5 Determination of ERS values for RIMM images ............................................................................ 20

© ISO 2022 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 22028-3:2022(E)

B.6 Use of XMP metadata with RIMM images ........................................................................................ 21

Bibliography .................................................................................................................................................... 22

Foreword ........................................................................................................................................................... iv

Introduction ....................................................................................................................................................... v

1 Scope ....................................................................................................................................................... 1

2 Normative references ........................................................................................................................ 1

3 Terms and definitions ....................................................................................................................... 1

4 Requirements ...................................................................................................................................... 5

4.1 General ................................................................................................................................................... 5

4.2 Adopted white ...................................................................................................................................... 6

4.3 Reference medium primaries and white point ......................................................................... 7

4.4 RIMM RGB, ERIMM RGB, FP-RIMM RGB colour image encoding .......................................... 7

4.4.1 Encoding principles ........................................................................................................................... 7

4.4.2 Tristimulus value normalization ................................................................................................... 8

4.4.3 RIMM RGB conversion matrix ......................................................................................................... 8

4.4.4 RIMM RGB colour component transfer function ...................................................................... 8

4.4.5 RIMM RGB digital encoding function ............................................................................................ 9

4.4.6 ERIMM RGB colour component transfer function .................................................................... 9

4.4.7 ERIMM RGB digital encoding function ......................................................................................... 9

4.4.8 FP-RIMM RGB colour component transfer function ............................................................. 10

4.5 Inverse RIMM RGB transformation ............................................................................................ 10

4.5.1 General ................................................................................................................................................ 10

4.5.2 Inverse RIMM RGB digital encoding function ......................................................................... 11

4.5.3 Inverse RIMM RGB colour component transfer function .................................................... 11

4.5.4 Inverse ERIMM RGB digital encoding function....................................................................... 11

4.5.5 Inverse ERIMM RGB colour component transfer function ................................................. 12

4.5.6 Inverse RIMM RGB conversion matrix ...................................................................................... 12

4.5.7 Inverse tristimulus value normalization ................................................................................. 12

4.5.8 Inverse FP-RIMM RGB colour component transfer function ............................................. 13

Annex A (informative) Example colour rendering transform from RIMM RGB to ROMM RGB

............................................................................................................................................................... 14

Annex B (informative) Cultural Heritage Applications of RIMM RGB ........................................... 19

Bibliography .................................................................................................................................................... 22

iv © ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 22028-3:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO

collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

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 ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directiveswww.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 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/patentswww.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 of 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

www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 42, Photography.

This third edition cancels and replaces the second edition (ISO/TS 22028-3:2012), which was a technical

Formatted: Font color: Dark Red, Strikethrough,

specification that has been revised to be an international standard. This first edition of ISO 22028-3:2022 Pattern: Clear

cancels and replaces the second edition (ISO/TS 22028-3:2012), which has been technically revised.

Formatted: Font color: Dark Red, Strikethrough,
Pattern: Clear
The main changes are as follows:
Formatted: Font color: Dark Red, Strikethrough,
Pattern: Clear
— the Kodak IP statement has been removed;
Formatted: Font color: Dark Red, Strikethrough,
— some references have been added, deleted, or updated; Pattern: Clear
Formatted: Font color: Dark Red, Strikethrough,
— Annex B has been added.
Pattern: Clear
Formatted: Pattern: Clear
A list of all parts in the ISO 22028 series can be found on the ISO website.
Formatted: Pattern: Clear

Any feedback or questions on this document should be directed to the user’s national standards body. A

Formatted: Pattern: Clear
complete listing of these bodies can be found at
www.iso.org/members.htmlwww.iso.org/members.html. Formatted: Pattern: Clear
© ISO 2022 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 22028-3:2022(E)
Introduction

This document has been developed in order to meet the industry need for a complete, fully-documented,

publicly-available definition of a wide-primary scene-referred extended colour gamut red-green-blue

(RGB) colour image encoding. This encoding provides a way to represent scene-referred images that does

not limit the colour gamut to those colours capable of being displayed on a CRT monitor or require the

use of negative RGB colourimetry coordinates.

A scene-referred extended colour gamut colour encoding is particularly desirable for professional

photography applications. For example, colours captured by digital cameras, as well as conventional

capture devices such as photographic film, can be outside those that can be represented within the colour

gamut of a typical monitor or other types of output devices. Similarly, scene-referred images can have a

larger luminance dynamic range than output-referred images since they have not been modified by a

colour rendering process to fit the images to a specific output medium applying appropriate tone and

colour reproduction aims. Retaining the unrendered scene-referred image data has the advantage that it

preserves the option to make decisions about how a particular image is to be rendered. For example, a

scene-referred image of a backlit scene can retain information about both the dark foreground region and

the bright background region of the scene. This information can be used to make a properly exposed print

of either the foreground region or the background region, or alternatively can be used to create an

improved image by rendering the two regions differently.

By using a standard scene-referred extended colour gamut colour image encoding, images can be stored,

interchanged and manipulated without restricting the image to a particular rendering intent or output

device. The reference input medium metric RGB (RIMM RGB) colour encoding specified in this document

meets the needs of these types of applications, as described in References [14] and [15]. An extended

Formatted: Pattern: Clear

dynamic range version of this colour image encoding known as extended reference input medium metric

Formatted: Pattern: Clear

RGB (ERIMM RGB), and a floating point version known as FP-RIMM RGB are also specified for use with

high-dynamic range input sources. The scene-referred RIMM RGB colour image encoding is intended to

be complementary to the output-referred ROMM RGB colour image encoding specified in ISO 22028-2

Formatted: Pattern: Clear
[10]

. Both colour encodings are based on the same “wide RGB” additive colour space to facilitate the

Formatted: Pattern: Clear

development of image processing algorithms and simple colour rendering transformations to convert

Formatted: Pattern: Clear
scene-referred RIMM RGB images to rendered output-referred ROMM RGB images.
Formatted: Pattern: Clear
vi © ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 22028-3:2022(E)
Photography and graphic technology — Extended colour
encodings for digital image storage, manipulation and
interchange — Part 3: Reference input medium metric RGB colour
image encoding (RIMM RGB)
1 Scope

This document specifies a family of scene-referred extended colour gamut RGB colour image encodings

designated as reference input medium metric RGB (RIMM RGB). Digital images encoded using RIMM RGB

can be manipulated, stored, transmitted, displayed or printed by digital still picture imaging systems.

Three precision levels are defined using 8-, 12- and 16-bits/channel.

An extended luminance dynamic range version of RIMM RGB is also defined, designated as extended

reference input medium metric RGB (ERIMM RGB). Two precision levels of ERIMM RGB are defined using

12- and 16-bits/channel.

FP-RIMM RGB, a floating point version of RIMM RGB, defines the expression method of RIMM RGB in a

floating point figure. Three precision levels of FP-RIMM RGB are defined using 16-, 32- and 64-

bits/channel.
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.

ISO 11664-1, Colorimetry — Part 1: CIE standard colorimetric observers

CIE Publication 15, Colorimetry
IEEE 754, IEEE Standard for Floating-Point Arithmetic
ISO/CIE 11664-1, Colorimetry — Part 1: CIE standard colorimetric observers
CIE Publication 15, Colorimetry
IEEE 754, IEEE Standard for Floating-Point Arithmetic
This International Standard replaces ISO/CIE 10527.
This International Standard replaces ISO/CIE 10527.
© ISO 2022 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO 22028-3:2022(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminologicalterminology databases for use in standardization at the following

addresses:

— ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp

Formatted: English (United States)
Formatted: Adjust space between Latin and Asian text,

— IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/

Adjust space between Asian text and numbers, Tab
stops: Not at 19.85 pt + 39.7 pt + 59.55 pt + 79.4 pt
3.1
+ 99.25 pt + 119.05 pt + 138.9 pt + 158.75 pt +
adapted white
178.6 pt + 198.45 pt

colour stimulus that an observer who is adapted to the viewing environment would judge to be perfectly

Formatted: Hyperlink, English (United States)

achromatic and to have a luminance factor of unity; i.e. absolute colourimetric coordinates that an

observer would consider to be a perfect white diffuser Formatted: English (United States)

Formatted: Hyperlink, English (United States)
Note 1 to entry: The adapted white can vary within a scene.
3.2
additive RGB colour space

colourimetric colour space having three colour primaries (generally red, green and blue) such that

CIE XYZ tristimulus values can be determined from the RGB colour space values by forming a weighted

combination of the CIE XYZ tristimulus values for the individual colour primaries, where the weights are

proportional to the radiometrically linear colour space values for the corresponding colour primaries

Note 1 to entry: A simple linear 3 × 3 matrix transformation can be used to transform between CIE XYZ

tristimulus values and the radiometrically linear colour space values for an additive RGB colour space.

Note 2 to entry: Additive RGB colour spaces are defined by specifying the CIE chromaticity values for a set of

additive RGB primaries and a colour space white point, together with a colour component transfer function.

3.3
adopted white

spectral radiance distribution as seen by an image capture or measurement device and converted to

colour signals that are considered to be perfectly achromatic and to have an observer adaptive luminance

factor of unity; i.e. colour signals that are considered to correspond to a perfect white diffuser

Note 1 to entry: The adopted white can vary within a scene, if such variation is supported by the imaging system.

Note 2 to entry: The adopted white is not required to be an estimate or approximation of the adapted white. For

example, if a scene lit by tungsten illumination is captured using a DSC with the white balance set to D55 (daylight),

the adopted white will be D55 but the adapted white will be closer to a tungsten illuminant (e.g. ISO 7589 Studio

Formatted: Pattern: Clear
[1]
Tungsten or CIE Illuminant A).
Formatted: Pattern: Clear

Note 3 to entry: The adopted white is not the same as the adapted white. See 3.1.

Formatted: Pattern: Clear
Formatted: Pattern: Clear
3.4
colourimetric colour space
colour space having an exact and simple relationship to CIE colourimetric values

Note 1 to entry: Colourimetric colour spaces include those defined by CIE (e.g. CIE XYZ, CIELAB, CIELUV), as well

as colour spaces that are simple transformations of those colour spaces (e.g. additive RGB colour spaces (3.2)).

Formatted: Pattern: Clear
3.5
2 © ISO 2022 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 22028-3:2022(E)
colour component transfer function

single variable, monotonic mathematical function applied individually to one or more colour channels of

a colour space (3.10)
Formatted: Pattern: Clear

Note 1 to entry: Colour component transfer functions are frequently used to account for the nonlinear response

of a reference device and/or to improve the visual uniformity of a colour space.

Note 2 to entry: Generally, colour component transfer functions will be nonlinear functions such as a power-law

(i.e. “gamma”) function or a logarithmic function. However, in some cases a linear colour component transfer

function can be used.
3.6
colour encoding

generic term for a quantized digital encoding of a colour space (3.10), encompassing both colour space

Formatted: Pattern: Clear
encodings (3.11) and colour image encodings (3.8)
Formatted: Pattern: Clear
Formatted: Pattern: Clear
3.7
colour gamut

solid in a colour space (3.10), consisting of all those colours that are either present in a specific scene,

Formatted: Pattern: Clear

artwork, photograph, photomechanical, or other reproduction, or capable of being created using a

particular output device and/or medium
3.8
colour image encoding

digital encoding of the colour values for a digital image, including the specification of a colour space

encoding (3.11), together with any information necessary to properly interpret the colour values such as

Formatted: Pattern: Clear
the image state, the intended image viewing environment and the reference medium

Note 1 to entry: In some cases, the intended image viewing environment will be explicitly defined for the colour

image encoding. In other cases, the intended image viewing environment can be specified on an image-by-image

basis using metadata associated with the digital image.

Note 2 to entry: Some colour image encodings will indicate particular reference medium characteristics, such as

a reflection print with a specified density range. In other cases, the reference medium will not be applicable, such

as with a scene-referred colour image encoding, or will be specified using image metadata.

Note 3 to entry: Colour image encodings are not limited to pictorial digital images that originate from an original

scene, but are also applicable to digital images with content such as text, line art, vector graphics and other forms

of original artwork.
3.9
colour rendering

mapping of image data representing the colour-space coordinates of the elements of a scene to output-

referred image data representing the colour space (3.10) coordinates of the elements of a reproduction

Formatted: Pattern: Clear

Note 1 to entry: Colour rendering generally consists of one or more of the following:

— compensating for differences in the input and output viewing conditions;

— tone scale and gamut mapping to map the scene colours onto the dynamic range and colour gamut (3.7) of the

Formatted: Pattern: Clear
reproduction;
— applying preference adjustments.
© ISO 2022 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO 22028-3:2022(E)
3.10
colour space
geometric representation of colours in space, usually of three dimensions
[SOURCE: CIE Publication 17.4:1987, 845-03-25]
Formatted: Pattern: Clear
Formatted: Pattern: Clear
3.11
Formatted: Pattern: Clear
colour space encoding

digital encoding of a colour space (3.10), including the specification of a digital encoding method, and a

Formatted: Pattern: Clear
colour space (3.10) value range
Formatted: Pattern: Clear

Note 1 to entry: Multiple colour space encodings can be defined based on a single colour space where the

Formatted: Pattern: Clear

different colour space encodings have different digital encoding methods and/or colour space value ranges. (For

Formatted: Pattern: Clear

example, 8-bit sRGB and 10-bit e-sRGB are different colour space encodings based on a particular RGB colour space.)

Formatted: Pattern: Clear
3.12
colour space white point
colour stimulus to which colour space (3.10) values are normalized
Formatted: Pattern: Clear

Note 1 to entry: It is not necessary that the colour space white point correspond to the assumed adapted white

point and/or the reference medium white point for a colour image encoding (3.8).
Formatted: Pattern: Clear
3.13
image state

attribute of a colour image encoding (3.8) indicating the rendering state of the image data

Formatted: Pattern: Clear

Note 1 to entry: The primary image states defined in this document are the scene-referred image state, the

original-referred image state and the output-referred image state.
3.14
luminance factor

ratio of the luminance of the surface element in the given direction to that of a perfect reflecting or

transmitting diffuser identically illuminated
[SOURCE: CIE Publication 17.4:1987, 845-04-69]
Formatted: Pattern: Clear
Formatted: Pattern: Clear
3.15
Formatted: Pattern: Clear
observer adaptive luminance factor

ratio of the luminance of a stimulus to the luminance of a stimulus that an observer adapted to the viewing

Formatted: Pattern: Clear
environment would interpret to be a perfect white diffuser
Formatted: Pattern: Clear
3.16 Formatted: Pattern: Clear
output-referred image state

image state (3.13) associated with image data that represents the colour space (3.10) coordinates of the

Formatted: Pattern: Clear

elements of an image that has undergone colour rendering (3.9) appropriate for a specified real or virtual

Formatted: Pattern: Clear
output device and viewing conditions
Formatted: Pattern: Clear

Note 1 to entry: When the phrase “output-referred” is used as a qualifier to an object, it implies that the object is

in an output-referred image state. For example, output-referred image data are image data in an output-referred

image state.
4 © ISO 2022 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 22028-3:2022(E)

Note 2 to entry: Output referred image data are referred to the specified output device and viewing conditions.

A single scene can be colour rendered to a variety of output-referred representations depending on the anticipated

output viewing conditions, media limitations and/or artistic intents.

Note 3 to entry: Output-referred image data can become the starting point for a subsequent reproduction

process. For example, sRGB output-referred image data are frequently considered to be the starting point for the

colour re-rendering performed by a printer designed to receive sRGB image data.
3.17
scene

spectral radiances of a view of the natural world as measured from a specified vantage point in space and

at a specified time
Note 1
...

INTERNATIONAL ISO
STANDARD 22028-3
First edition
2023-01
Photography and graphic
technology — Extended colour
encodings for digital image storage,
manipulation and interchange —
Part 3:
Reference input medium metric RGB
colour image encoding (RIMM RGB)
Photographie et technologie graphique — Codages par couleurs
étendues pour stockage, manipulation et échange d'image
numérique —
Partie 3: Codage d'image en couleurs RVB par référence d'entrée par
voie métrique
PROOF/ÉPREUVE
Reference number
ISO 22028-3:2023(E)
© ISO 2023
---------------------- Page: 1 ----------------------
ISO 22028-3:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023

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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE © ISO 2023 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 22028-3:2023(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Requirements .......................................................................................................................................................................................................... 5

4.1 General ........................................................................................................................................................................................................... 5

4.2 Adopted white ......................................................................................................................................................................................... 7

4.3 Reference medium primaries and white point .......................................................................................................... 7

4.4 RIMM RGB, ERIMM RGB, FP-RIMM RGB colour image encoding ............................................................... 7

4.4.1 Encoding principles ......................................................................................................................................................... 7

4.4.2 Tristimulus value normalization ......................................................................................................................... 8

4.4.3 RIMM RGB conversion matrix ................................................................................................................................ 8

4.4.4 RIMM RGB colour component transfer function .................................................................................... 9

4.4.5 RIMM RGB digital encoding function ............................................................................................................... 9

4.4.6 ERIMM RGB colour component transfer function ................................................................................ 9

4.4.7 ERIMM RGB digital encoding function ........................................................................................................ 10

4.4.8 FP-RIMM RGB colour component transfer function ........................................................................ 11

4.5 Inverse RIMM RGB transformation ................................................................................................................................... 11

4.5.1 General ..................................................................................................................................................................................... 11

4.5.2 Inverse RIMM RGB digital encoding function ....................................................................................... 11

4.5.3 Inverse RIMM RGB colour component transfer function ............................................................12

4.5.4 Inverse ERIMM RGB digital encoding function ....................................................................................12

4.5.5 Inverse ERIMM RGB colour component transfer function .........................................................13

4.5.6 Inverse RIMM RGB conversion matrix ......................................................................................................... 13

4.5.7 Inverse tristimulus value normalization ...................................................................................................13

4.5.8 Inverse FP-RIMM RGB colour component transfer function .................................................... 14

Annex A (informative) Example colour rendering transform from RIMM RGB to ROMM RGB ..........15

Annex B (informative) Cultural heritage applications of RIMM RGB.............................................................................20

Bibliography .............................................................................................................................................................................................................................24

iii
© ISO 2023 – All rights reserved PROOF/ÉPREUVE
---------------------- Page: 3 ----------------------
ISO 22028-3:2023(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

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 ISO documents 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 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 of 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

www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 42, Photography.

This first edition of ISO 22028-3:2022 cancels and replaces the second edition (ISO/TS 22028-3:2012),

which has been technically revised.
The main changes are as follows:
— the Kodak IP statement has been removed;
— some references have been added, deleted, or updated;
— Annex B has been added.
A list of all parts in the ISO 22028 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
PROOF/ÉPREUVE © ISO 2023 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 22028-3:2023(E)
Introduction

This document has been developed in order to meet the industry need for a complete, fully-documented,

publicly-available definition of a wide-primary scene-referred extended colour gamut red-green-blue

(RGB) colour image encoding. This encoding provides a way to represent scene-referred images that

does not limit the colour gamut to those colours capable of being displayed on a CRT monitor or require

the use of negative RGB colourimetry coordinates.

A scene-referred extended colour gamut colour encoding is particularly desirable for professional

photography applications. For example, colours captured by digital cameras, as well as conventional

capture devices such as photographic film, can be outside those that can be represented within the

colour gamut of a typical monitor or other types of output devices. Similarly, scene-referred images can

have a larger luminance dynamic range than output-referred images since they have not been modified

by a colour rendering process to fit the images to a specific output medium applying appropriate tone

and colour reproduction aims. Retaining the unrendered scene-referred image data has the advantage

that it preserves the option to make decisions about how a particular image is to be rendered.

For example, a scene-referred image of a backlit scene can retain information about both the dark

foreground region and the bright background region of the scene. This information can be used to make

a properly exposed print of either the foreground region or the background region, or alternatively can

be used to create an improved image by rendering the two regions differently.

By using a standard scene-referred extended colour gamut colour image encoding, images can be

stored, interchanged and manipulated without restricting the image to a particular rendering intent

or output device. The reference input medium metric RGB (RIMM RGB) colour encoding specified in

this document meets the needs of these types of applications, as described in References [14] and

[15]. An extended dynamic range version of this colour image encoding known as extended reference

input medium metric RGB (ERIMM RGB), and a floating point version known as FP-RIMM RGB are also

specified for use with high-dynamic range input sources. The scene-referred RIMM RGB colour image

encoding is intended to be complementary to the output-referred ROMM RGB colour image encoding

[10]

specified in ISO 22028-2 . Both colour encodings are based on the same “wide RGB” additive colour

space to facilitate the development of image processing algorithms and simple colour rendering

transformations to convert scene-referred RIMM RGB images to rendered output-referred ROMM RGB

images.
© ISO 2023 – All rights reserved PROOF/ÉPREUVE
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 22028-3:2023(E)
Photography and graphic technology — Extended colour
encodings for digital image storage, manipulation and
interchange —
Part 3:
Reference input medium metric RGB colour image
encoding (RIMM RGB)
1 Scope

This document specifies a family of scene-referred extended colour gamut RGB colour image encodings

designated as reference input medium metric RGB (RIMM RGB). Digital images encoded using RIMM RGB

can be manipulated, stored, transmitted, displayed or printed by digital still picture imaging systems.

Three precision levels are defined using 8-, 12- and 16-bits/channel.

An extended luminance dynamic range version of RIMM RGB is also defined, designated as extended

reference input medium metric RGB (ERIMM RGB). Two precision levels of ERIMM RGB are defined

using 12- and 16-bits/channel.

FP-RIMM RGB, a floating point version of RIMM RGB, defines the expression method of RIMM RGB in

a floating point figure. Three precision levels of FP-RIMM RGB are defined using 16-, 32- and 64-bits/

channel.
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.

ISO/CIE 11664-1, Colorimetry — Part 1: CIE standard colorimetric observers
CIE Publication 15, Colorimetry
IEEE 754, IEEE Standard for Floating-Point Arithmetic
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
1) This International Standard replaces ISO/CIE 10527.
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ISO 22028-3:2023(E)
3.1
adapted white

colour stimulus that an observer who is adapted to the viewing environment would judge to be perfectly

achromatic and to have a luminance factor of unity; i.e. absolute colourimetric coordinates that an

observer would consider to be a perfect white diffuser
Note 1 to entry: The adapted white can vary within a scene.
3.2
additive RGB colour space

colourimetric colour space having three colour primaries (generally red, green and blue) such that

CIE XYZ tristimulus values can be determined from the RGB colour space values by forming a weighted

combination of the CIE XYZ tristimulus values for the individual colour primaries, where the weights are

proportional to the radiometrically linear colour space values for the corresponding colour primaries

Note 1 to entry: A simple linear 3 × 3 matrix transformation can be used to transform between CIE XYZ

tristimulus values and the radiometrically linear colour space values for an additive RGB colour space.

Note 2 to entry: Additive RGB colour spaces are defined by specifying the CIE chromaticity values for a set of

additive RGB primaries and a colour space white point, together with a colour component transfer function.

3.3
adopted white

spectral radiance distribution as seen by an image capture or measurement device and converted

to colour signals that are considered to be perfectly achromatic and to have an observer adaptive

luminance factor of unity; i.e. colour signals that are considered to correspond to a perfect white

diffuser

Note 1 to entry: The adopted white can vary within a scene, if such variation is supported by the imaging system.

Note 2 to entry: The adopted white is not required to be an estimate or approximation of the adapted white.

For example, if a scene lit by tungsten illumination is captured using a DSC with the white balance set to D55

(daylight), the adopted white will be D55 but the adapted white will be closer to a tungsten illuminant (e.g.

[1]
ISO 7589 Studio Tungsten or CIE Illuminant A).

Note 3 to entry: The adopted white is not the same as the adapted white. See 3.1.

3.4
colourimetric colour space
colour space having an exact and simple relationship to CIE colourimetric values

Note 1 to entry: Colourimetric colour spaces include those defined by CIE (e.g. CIE XYZ, CIELAB, CIELUV), as well

as colour spaces that are simple transformations of those colour spaces (e.g. additive RGB colour spaces (3.2)).

3.5
colour component transfer function

single variable, monotonic mathematical function applied individually to one or more colour channels

of a colour space (3.10)

Note 1 to entry: Colour component transfer functions are frequently used to account for the nonlinear response

of a reference device and/or to improve the visual uniformity of a colour space.

Note 2 to entry: Generally, colour component transfer functions will be nonlinear functions such as a power-law

(i.e. “gamma”) function or a logarithmic function. However, in some cases a linear colour component transfer

function can be used.
3.6
colour encoding

generic term for a quantized digital encoding of a colour space (3.10), encompassing both colour space

encodings (3.11) and colour image encodings (3.8)
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ISO 22028-3:2023(E)
3.7
colour gamut

solid in a colour space (3.10), consisting of all those colours that are either present in a specific scene,

artwork, photograph, photomechanical, or other reproduction, or capable of being created using a

particular output device and/or medium
3.8
colour image encoding

digital encoding of the colour values for a digital image, including the specification of a colour space

encoding (3.11), together with any information necessary to properly interpret the colour values such

as the image state, the intended image viewing environment and the reference medium

Note 1 to entry: In some cases, the intended image viewing environment will be explicitly defined for the colour

image encoding. In other cases, the intended image viewing environment can be specified on an image-by-image

basis using metadata associated with the digital image.

Note 2 to entry: Some colour image encodings will indicate particular reference medium characteristics, such as

a reflection print with a specified density range. In other cases, the reference medium will not be applicable, such

as with a scene-referred colour image encoding, or will be specified using image metadata.

Note 3 to entry: Colour image encodings are not limited to pictorial digital images that originate from an original

scene, but are also applicable to digital images with content such as text, line art, vector graphics and other forms

of original artwork.
3.9
colour rendering

mapping of image data representing the colour-space coordinates of the elements of a scene to output-

referred image data representing the colour space (3.10) coordinates of the elements of a reproduction

Note 1 to entry: Colour rendering generally consists of one or more of the following:

— compensating for differences in the input and output viewing conditions;

— tone scale and gamut mapping to map the scene colours onto the dynamic range and colour gamut (3.7) of the

reproduction;
— applying preference adjustments.
3.10
colour space
geometric representation of colours in space, usually of three dimensions
[SOURCE: CIE Publication 17.4:1987, 845-03-25]
3.11
colour space encoding

digital encoding of a colour space (3.10), including the specification of a digital encoding method, and a

colour space (3.10) value range

Note 1 to entry: Multiple colour space encodings can be defined based on a single colour space where the different

colour space encodings have different digital encoding methods and/or colour space value ranges. (For example,

8-bit sRGB and 10-bit e-sRGB are different colour space encodings based on a particular RGB colour space.)

3.12
colour space white point
colour stimulus to which colour space (3.10) values are normalized

Note 1 to entry: It is not necessary that the colour space white point correspond to the assumed adapted white

point and/or the reference medium white point for a colour image encoding (3.8).
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3.13
image state

attribute of a colour image encoding (3.8) indicating the rendering state of the image data

Note 1 to entry: The primary image states defined in this document are the scene-referred image state, the

original-referred image state and the output-referred image state.
3.14
luminance factor

ratio of the luminance of the surface element in the given direction to that of a perfect reflecting or

transmitting diffuser identically illuminated
[SOURCE: CIE Publication 17.4:1987, 845-04-69]
3.15
observer adaptive luminance factor

ratio of the luminance of a stimulus to the luminance of a stimulus that an observer adapted to the

viewing environment would interpret to be a perfect white diffuser
3.16
output-referred image state

image state (3.13) associated with image data that represents the colour space (3.10) coordinates of

the elements of an image that has undergone colour rendering (3.9) appropriate for a specified real or

virtual output device and viewing conditions

Note 1 to entry: When the phrase “output-referred” is used as a qualifier to an object, it implies that the object is

in an output-referred image state. For example, output-referred image data are image data in an output-referred

image state.

Note 2 to entry: Output referred image data are referred to the specified output device and viewing conditions. A

single scene can be colour rendered to a variety of output-referred representations depending on the anticipated

output viewing conditions, media limitations and/or artistic intents.

Note 3 to entry: Output-referred image data can become the starting point for a subsequent reproduction process.

For example, sRGB output-referred image data are frequently considered to be the starting point for the colour

re-rendering performed by a printer designed to receive sRGB image data.
3.17
scene

spectral radiances of a view of the natural world as measured from a specified vantage point in space

and at a specified time

Note 1 to entry: A scene can correspond to an actual view of the natural world or to a computer-generated virtual

scene simulating such a view.
3.18
scene-referred image state

image state (3.13) associated with image data that represents estimates of the colour space (3.10)

coordinates of the elements of a scene

Note 1 to entry: When the phrase “scene-referred” is used as a qualifier to an object, it implies that the object is

in a scene-referred image state. For example, scene-referred image data are image data in a scene-referred image

state.

Note 2 to entry: Scene-referred image data can be determined from raw DSC image data before colour rendering

(3.9) is performed. Generally, DSCs do not write scene-referred image data in image files, but some do so in a

special mode intended for this purpose. Typically, DSCs write standard output-referred image data where colour

rendering has already been performed.

Note 3 to entry: Scene-referred image data typically represents relative scene colourimetry estimates.

Absolute scene colourimetry estimates can be calculated using a scaling factor. The scaling factor can be

derived from additional information such as the image OECF, FNumber or ApertureValue, and ExposureTime or

ShutterSpeedValue tags.
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ISO 22028-3:2023(E)

Note 4 to entry: Scene-referred image data can contain inaccuracies due to the dynamic range limitations of the

capture device, noise from various sources, quantization, optical blurring and flare that are not corrected for,

and colour analysis errors due to capture device metamerism. In some cases, these sources of inaccuracy can be

significant.

Note 5 to entry: The transformation from raw DSC image data to scene-referred image data depends on the

relative adopted whites (3.3) selected for the scene and the colour space used to encode the image data. If the

chosen scene adopted white is inappropriate, additional errors will be introduced into the scene-referred image

data. These errors can be correctable if the transformation used to produce the scene-referred image data are

known, and the colour encoding (3.6) used for the incorrect scene-referred image data has adequate precision

and dynamic range.

Note 6 to entry: The scene can correspond to an actual view of the natural world, or be a computer-generated

virtual scene simulating such a view. It can also correspond to a modified scene determined by applying

modifications to an original scene to produce some different desired scene. Any such scene modifications need to

leave the image in a scene-referred image state and need to be done in the context of an expected colour rendering

(3.9) transform.
3.19
tristimulus value

amounts of the three reference colour stimuli, in a given trichromatic system, required to match the

colour of the stimulus considered
[SOURCE: CIE Publication 17.4:1987, 845-03-22]
3.20
veiling glare

light, reflected from an imaging medium, that has not been modulated by the means used to produce

the image

Note 1 to entry: Veiling glare lightens and reduces the contrast of the darker parts of an image.

[12]

Note 2 to entry: In CIE Publication 122 , the veiling glare of a CRT display is referred to as ambient flare.

3.21
viewing flare

veiling glare that is observed in a viewing environment but not accounted for in radiometric

measurements made using a prescribed measurement geometry

Note 1 to entry: The viewing flare is expressed as a percentage of the luminance of adapted white.

3.22
working colour space

colour space encoding (3.11) in which operations such as image edits, enhancements, or colour rendering

(3.9) are performed

Note 1 to entry: The image state in a working colour space can change as operations are performed.

Note 2 to entry: If operations performed in a working colour space are guided by viewing the image on a medium,

that medium and the associated viewing conditions become the reference for the resulting image.

4 Requirements
4.1 General

Reference input medium metric RGB (RIMM RGB) and the ERIMM and FP-RIMM associated versions

of RIMM RGB are extended colour gamut RGB colour image encodings of the colourimetry of a scene-

referred image, white balanced to be relative to a specified adopted white. The image colourimetry is

encoded in terms of an additive RGB colour space (i.e. a colourimetric colour space) associated with a

hypothetical additive colour device having a specified set of primaries and no cross-talk between the

colour channels. The RIMM RGB colour image encoding has a maximum luminance value corresponding

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ISO 22028-3:2023(E)

to 200 % of a perfect diffuse reflector (i.e. an observer adaptive luminance factor of 2,0). Extended

reference input medium metric RGB (ERIMM RGB) is an extended luminance dynamic range version

of RIMM RGB having a maximum observer adaptive luminance factor of about 316. The maximum

luminance value of FP-RIMM RGB colour image encoding is limited only by the floating point encoding

range. In RIMM RGB, ERIMM RGB and FP-RIMM RGB, the image colourimetry shall be based on flareless

(or flare corrected) colourimetric measurements as described in CIE Publication 15 using the CIE 1931

standard colourimetric observer defined in ISO/CIE 11664-1.

Scene-referred image data may correspond to an actual view of the natural world, or a simulation of

such a view. It may also correspond to a modified scene determined by applying modifications to an

original scene. In order to be appropriate for encoding as RIMM RGB, ERIMM RGB or FP-RIMM RGB, any

scene modifications shall leave the image in a scene-referred image state.

Scene-referred image data may have an associated pre-determined colour rendering transform. When

an associated pre-determined colour rendering transform is present with scene-referred image data,

such an intended colour rendering transform should be included in any image preview path that is used

to provide subjective feedback to a user, unless

— the user has selected direct viewing of the scene-referred image and intends that modifications are

to be previewed in the scene-referred state, and

— the scene-referred image data has been converted to an appropriate working colour space for manual

editing and colour rendering. In this case the user may exercise the option to apply or not apply an

associated pre-determined colour rendering transform, if present, when the scene-referred image

data are converted to the working colour space.

EXAMPLES Scene modifications could include removing haze from the captured image or allowing a user

to manually adjust the exposure/white balance. It could also include more complex operations such as using a

“dodge-and-burn” algorithm to correct over-exposed regions of a backlit scene. (This can be viewed as being

analogous to “re-lighting” the scene.) Scene modifications could also include applying desired changes to the

scene such as simulating a “night” scene, making grass greener to make it look healthier, or making the sky bluer

to make it look clearer. However, typical colour rendering transforms will include a boost in the midtone contrast

and chroma of the image. Consequently, any boost in colourfulness of the scene (e.g. making the grass greener)

needs to be done wit
...

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