Image technology colour management -- Black point compensation

ISO 18619:2015 specifies a procedure, including computation, by which a transform between ICC profiles can be adjusted (compensated) to take into account differences between the dark end of the source colour space and the dark end of the destination colour space. This is referred to as black point compensation (BPC). The relative colorimetric encoding of ICC profile transforms already provides a mechanism for such adjustment of the light (white) end of the tone scale.

Gestion de couleur en technologie d'image -- Compensation du point noir

Barvno upravljanje upodobitvenih tehnologij - Kompenzacija črne točke

General Information

Status
Published
Publication Date
18-Jun-2015
Current Stage
9093 - International Standard confirmed
Start Date
03-Sep-2020

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INTERNATIONAL ISO
STANDARD 18619
First edition
2015-07-01
Image technology colour
management — Black point
compensation
Gestion de couleur en technologie d’image — Compensation du point
noir
Reference number
ISO 18619:2015(E)
ISO 2015
---------------------- Page: 1 ----------------------
ISO 18619:2015(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2015, Published in Switzerland

All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2015 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 18619:2015(E)
Contents Page

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

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

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

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

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

4 Requirements .......................................................................................................................................................................................................... 2

4.1 Constraints ................................................................................................................................................................................................. 2

4.2 Computation.............................................................................................................................................................................................. 3

4.2.1 Outline ...................................................................................................................................................................................... 3

4.2.2 Functions used ................................................................................................................................................................... 3

4.2.3 Computing the SourceBlackPoint ...................................................................................................................... 4

4.2.4 Computing the DestinationBlackPoint for ICC profiles that are not LUT-based ....... 4

4.2.5 Computing the DestinationBlackPoint for ICC profiles that are LUT-based ................. 5

4.2.6 Computing the mapping from SourceBlackPoint to DestinationBlackPoint .............10

4.2.7 Applying the black point compensation in a colour conversion ..........................................11

Annex A (informative) Why black point compensation is neccessary ............................................................................12

Bibliography .............................................................................................................................................................................................................................14

© ISO 2015 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 18619:2015(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 on the meaning of ISO specific terms and expressions related to conformity

assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers

to Trade (TBT) see the following URL: Foreword - Supplementary information

The committee responsible for this document is ISO/TC 130, Graphic technology, in cooperation with the

International Color Consortium.
iv © ISO 2015 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 18619:2015(E)
Introduction

Black point compensation (BPC) is a technique used to address colour conversion problems caused by

differences between the darkest level of black achievable on one device and the darkest level of black

achievable on another. This procedure was first implemented in Adobe Photoshop in the late 1990s.

The International Color Consortium (ICC) and ISO Technical Committee 130 (Graphic technology) have

created this document to allow black point compensation to be used in a consistent manner across

applications.

The purpose of BPC is to adjust a colour transform between the colour spaces of source and destination

ICC profiles, so that it retains shadow details and utilizes available black levels. The procedure depends

only on the rendering intent(s) and the source and destination ICC profiles, not on any points in a

particular image. Therefore, the colour transform using specific source and destination ICC profiles and

rendering intent can be computed once, and then efficiently applied to many images which use the same

ICC profile colour transform pair and rendering intent.
© ISO 2015 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 18619:2015(E)
Image technology colour management — Black point
compensation
1 Scope

This International Standard specifies a procedure, including computation, by which a transform between

ICC profiles can be adjusted (compensated) to take into account differences between the dark end of the

source colour space and the dark end of the destination colour space. This is referred to as black point

compensation (BPC). The relative colorimetric encoding of ICC profile transforms already provides a

mechanism for such adjustment of the light (white) end of the tone scale.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

ISO 15076-1, Image technology colour management — Architecture, profile format and data structure —

Part 1: Based on ICC.1:2010
ICC.1:2001-04, File Format for Color Profiles
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 15076-1 and the following

apply.
3.1
DestinationBlackPoint

coordinate representing a dark neutral reproducible colour in the destination colour gamut

3.2
DestinationProfile

ICC profile, containing the transform from profile connection space to the destination device colour

space
3.3
SourceBlackPoint
coordinate representing a dark neutral colour in the source colour gamut
3.4
SourceProfile

ICC profile, containing the transform from the source device colour space to the profile connection space

3.5
RenderingIntent

rendering intent of the conversion from a source ICC profile’s colour space to a destination ICC profile’s

colour space
3.6
LabIdentityProfile

real or virtual ICC profile that contains a bi-directional (identity) transform between CIELAB and

PCSLAB
© ISO 2015 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 18619:2015(E)
3.7
black point compensation
BPC

computational procedure by which a transform between the colour spaces of ICC profiles can be adjusted

(compensated) to take into account differences between the dark end of the source colour space and the

dark end of the destination colour space
3.8
L, a, b
L*, a*, or b* component of the CIELAB colour space
3.9
output-capable CMYK profile

CMYK profile containing a transform from the ICC PCS encoding to the colour space encoding

3.10
transform

mathematical operations that define the change in representation of a colour between two colour spaces

3.11
gamut
range of colours that a given system is capable of reproducing
4 Requirements
4.1 Constraints

The black point compensation procedure defined in this International Specification shall take as its

inputs a destination ICC profile, a source ICC profile, and a rendering intent (in this International

Standard called DestinationProfile, SourceProfile and RenderingIntent respectively).

Applications that apply black point compensation shall support ICC profiles that conform to ISO 15076-1

and ICC profiles that conform to ICC.1:2001-04.

NOTE 1 This requirement ensures that processing applications will properly process all Version 2 and Version

4 ICC profiles.

NOTE 2 ISO 15076-1 provides a description of source and destination ICC profiles.

The rendering intent shall be one of: RelativeColorimetric; Perceptual; or Saturation. The rendering

intent used with DestinationProfile shall be the same as the rendering intent used with SourceProfile.

Black point compensation is not appropriate for the AbsoluteColorimetric rendering intent.

The versions of SourceProfile and DestinationProfile do not need to match.

SourceProfile and DestinationProfile types shall be Input, Display, Output, or ColorSpace. The types of

SourceProfile and DestinationProfile do not need to match.

DestinationProfile shall contain a transform from the ICC PCS encoding to the colour space encoding.

The data colour spaces of the SourceProfile and DestinationProfile shall be Gray, RGB, CMYK or CIELAB.

The data colour spaces of SourceProfile and DestinationProfile do not need to match.

NOTE 3 Some implementations of BPC extend to additional colour spaces or mixed rendering intents. The way

in which BPC operates in these cases is outside the scope of this International Standard.

2 © ISO 2015 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 18619:2015(E)
4.2 Computation
4.2.1 Outline

Black point compensation shall be performed according to the following procedure:

a) the SourceBlackPoint of SourceProfile shall be calculated as specified in 4.2.3;

b) the DestinationBlackPoint of DestinationProfile shall be calculated as specified in 4.2.4 and 4.2.5;

c) a mapping from SourceBlackPoint to DestinationBlackPoint shall be calculated as specified in 4.2.6;

d) the mapping shall be applied in a colour conversion as specified in 4.2.7.
4.2.2 Functions used
4.2.2.1 Colour transform with profiles

T shall denote a function to transform a point in the data colour space of Profile1 to a point in the device

colour space of Profile2, using a rendering intent, such that
y = T (x, Profile1, Profile2, Intent) (1)
where
x is a point in the data colour space of Profile1;
y is a point in the data colour space of Profile2;
Intent is the rendering intent.
4.2.2.2 Darkest colour of a profile

D shall denote a function to provide the darkest colour coordinate in the data colour space of Profile for

a rendering intent, such that
dc = D (Profile, Intent) (2)
where
dc is the darkest colour
Profile is the profile being evaluated,
Intent is the rendering intent.
dc shall be determined as follows:

A subset of the vertices within the data colour space of Profile, V, shall be defined as follows.

If the data colour space of Profile is Gray
V shall be the set of {(0) (1)}.
If the data colour space of Profile is RGB
V shall be the set of {(0, 0, 0) (1, 1, 1)}.
If the data colour space of Profile is CMYK
V shall be the set of {(0, 0, 0, 0) (1, 1, 1, 1) (0, 0, 0, 1) (1, 1, 1, 0)}.
© ISO 2015 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 18619:2015(E)
...

SLOVENSKI STANDARD
SIST ISO 18619:2020
01-april-2020
Barvno upravljanje upodobitvenih tehnologij - Kompenzacija črne točke
Image technology colour management - Black point compensation
Gestion de couleur en technologie d'image - Compensation du point noir
Ta slovenski standard je istoveten z: ISO 18619:2015
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
35.240.30 Uporabniške rešitve IT v IT applications in information,
informatiki, dokumentiranju in documentation and
založništvu publishing
37.100.99 Drugi standardi v zvezi z Other standards related to
grafično tehnologijo graphic technology
SIST ISO 18619:2020 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST ISO 18619:2020
---------------------- Page: 2 ----------------------
SIST ISO 18619:2020
INTERNATIONAL ISO
STANDARD 18619
First edition
2015-07-01
Image technology colour
management — Black point
compensation
Gestion de couleur en technologie d’image — Compensation du point
noir
Reference number
ISO 18619:2015(E)
ISO 2015
---------------------- Page: 3 ----------------------
SIST ISO 18619:2020
ISO 18619:2015(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2015, Published in Switzerland

All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2015 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 18619:2020
ISO 18619:2015(E)
Contents Page

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

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

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

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

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

4 Requirements .......................................................................................................................................................................................................... 2

4.1 Constraints ................................................................................................................................................................................................. 2

4.2 Computation.............................................................................................................................................................................................. 3

4.2.1 Outline ...................................................................................................................................................................................... 3

4.2.2 Functions used ................................................................................................................................................................... 3

4.2.3 Computing the SourceBlackPoint ...................................................................................................................... 4

4.2.4 Computing the DestinationBlackPoint for ICC profiles that are not LUT-based ....... 4

4.2.5 Computing the DestinationBlackPoint for ICC profiles that are LUT-based ................. 5

4.2.6 Computing the mapping from SourceBlackPoint to DestinationBlackPoint .............10

4.2.7 Applying the black point compensation in a colour conversion ..........................................11

Annex A (informative) Why black point compensation is neccessary ............................................................................12

Bibliography .............................................................................................................................................................................................................................14

© ISO 2015 – All rights reserved iii
---------------------- Page: 5 ----------------------
SIST ISO 18619:2020
ISO 18619:2015(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 on the meaning of ISO specific terms and expressions related to conformity

assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers

to Trade (TBT) see the following URL: Foreword - Supplementary information

The committee responsible for this document is ISO/TC 130, Graphic technology, in cooperation with the

International Color Consortium.
iv © ISO 2015 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 18619:2020
ISO 18619:2015(E)
Introduction

Black point compensation (BPC) is a technique used to address colour conversion problems caused by

differences between the darkest level of black achievable on one device and the darkest level of black

achievable on another. This procedure was first implemented in Adobe Photoshop in the late 1990s.

The International Color Consortium (ICC) and ISO Technical Committee 130 (Graphic technology) have

created this document to allow black point compensation to be used in a consistent manner across

applications.

The purpose of BPC is to adjust a colour transform between the colour spaces of source and destination

ICC profiles, so that it retains shadow details and utilizes available black levels. The procedure depends

only on the rendering intent(s) and the source and destination ICC profiles, not on any points in a

particular image. Therefore, the colour transform using specific source and destination ICC profiles and

rendering intent can be computed once, and then efficiently applied to many images which use the same

ICC profile colour transform pair and rendering intent.
© ISO 2015 – All rights reserved v
---------------------- Page: 7 ----------------------
SIST ISO 18619:2020
---------------------- Page: 8 ----------------------
SIST ISO 18619:2020
INTERNATIONAL STANDARD ISO 18619:2015(E)
Image technology colour management — Black point
compensation
1 Scope

This International Standard specifies a procedure, including computation, by which a transform between

ICC profiles can be adjusted (compensated) to take into account differences between the dark end of the

source colour space and the dark end of the destination colour space. This is referred to as black point

compensation (BPC). The relative colorimetric encoding of ICC profile transforms already provides a

mechanism for such adjustment of the light (white) end of the tone scale.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

ISO 15076-1, Image technology colour management — Architecture, profile format and data structure —

Part 1: Based on ICC.1:2010
ICC.1:2001-04, File Format for Color Profiles
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 15076-1 and the following

apply.
3.1
DestinationBlackPoint

coordinate representing a dark neutral reproducible colour in the destination colour gamut

3.2
DestinationProfile

ICC profile, containing the transform from profile connection space to the destination device colour

space
3.3
SourceBlackPoint
coordinate representing a dark neutral colour in the source colour gamut
3.4
SourceProfile

ICC profile, containing the transform from the source device colour space to the profile connection space

3.5
RenderingIntent

rendering intent of the conversion from a source ICC profile’s colour space to a destination ICC profile’s

colour space
3.6
LabIdentityProfile

real or virtual ICC profile that contains a bi-directional (identity) transform between CIELAB and

PCSLAB
© ISO 2015 – All rights reserved 1
---------------------- Page: 9 ----------------------
SIST ISO 18619:2020
ISO 18619:2015(E)
3.7
black point compensation
BPC

computational procedure by which a transform between the colour spaces of ICC profiles can be adjusted

(compensated) to take into account differences between the dark end of the source colour space and the

dark end of the destination colour space
3.8
L, a, b
L*, a*, or b* component of the CIELAB colour space
3.9
output-capable CMYK profile

CMYK profile containing a transform from the ICC PCS encoding to the colour space encoding

3.10
transform

mathematical operations that define the change in representation of a colour between two colour spaces

3.11
gamut
range of colours that a given system is capable of reproducing
4 Requirements
4.1 Constraints

The black point compensation procedure defined in this International Specification shall take as its

inputs a destination ICC profile, a source ICC profile, and a rendering intent (in this International

Standard called DestinationProfile, SourceProfile and RenderingIntent respectively).

Applications that apply black point compensation shall support ICC profiles that conform to ISO 15076-1

and ICC profiles that conform to ICC.1:2001-04.

NOTE 1 This requirement ensures that processing applications will properly process all Version 2 and Version

4 ICC profiles.

NOTE 2 ISO 15076-1 provides a description of source and destination ICC profiles.

The rendering intent shall be one of: RelativeColorimetric; Perceptual; or Saturation. The rendering

intent used with DestinationProfile shall be the same as the rendering intent used with SourceProfile.

Black point compensation is not appropriate for the AbsoluteColorimetric rendering intent.

The versions of SourceProfile and DestinationProfile do not need to match.

SourceProfile and DestinationProfile types shall be Input, Display, Output, or ColorSpace. The types of

SourceProfile and DestinationProfile do not need to match.

DestinationProfile shall contain a transform from the ICC PCS encoding to the colour space encoding.

The data colour spaces of the SourceProfile and DestinationProfile shall be Gray, RGB, CMYK or CIELAB.

The data colour spaces of SourceProfile and DestinationProfile do not need to match.

NOTE 3 Some implementations of BPC extend to additional colour spaces or mixed rendering intents. The way

in which BPC operates in these cases is outside the scope of this International Standard.

2 © ISO 2015 – All rights reserved
---------------------- Page: 10 ----------------------
SIST ISO 18619:2020
ISO 18619:2015(E)
4.2 Computation
4.2.1 Outline

Black point compensation shall be performed according to the following procedure:

a) the SourceBlackPoint of SourceProfile shall be calculated as specified in 4.2.3;

b) the DestinationBlackPoint of DestinationProfile shall be calculated as specified in 4.2.4 and 4.2.5;

c) a mapping from SourceBlackPoint to DestinationBlackPoint shall be calculated as specified in 4.2.6;

d) the mapping shall be applied in a colour conversion as specified in 4.2.7.
4.2.2 Functions used
4.2.2.1 Colour transform with profiles

T shall denote a function to transform a point in the data colour space of Profile1 to a point in the device

colour space of Profile2, using a rendering intent, such that
y = T (x, Profile1, Profile2, Intent) (1)
where
x is a point in the data colour space of Profile1;
y is a point in the data colour space of Profile2;
Intent is the rendering intent.
4.2.2.2 Darkest colour of a profile

D shall denote a function to provide the darkest colour coordinate in the data colour space of Profile for

a rendering intent, such that
dc = D (Profile, Intent) (2)
where
dc is the darkest colour
Profile is the profile being evaluated,
Intent is the rendering inte
...

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