1、BSI Standards PublicationBS ISO 18619:2015Image technology colourmanagement Black pointcompensationBS ISO 18619:2015 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 18619:2015.The UK participation in its preparation was entrusted to TechnicalCommittee PAI/43, G
2、raphic technology.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2015. Publish
3、ed by BSI StandardsLimited 2015ISBN 978 0 580 83936 8ICS 35.240.30; 37.100.99Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 30 June 2015.Amendments issued since p
4、ublicationDate Text affectedBS ISO 18619:2015 ISO 2015Image technology colour management Black point compensationGestion de couleur en technologie dimage Compensation du point noirINTERNATIONAL STANDARDISO18619First edition2015-07-01Reference numberISO 18619:2015(E)BS ISO 18619:2015ISO 18619:2015(E)
5、ii ISO 2015 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2015, Published in SwitzerlandAll 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
6、 on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 74
7、9 09 47copyrightiso.orgwww.iso.orgBS ISO 18619:2015ISO 18619:2015(E)Foreword ivIntroduction v1 Scope . 12 Normative references 13 Terms and definitions . 14 Requirements 24.1 Constraints . 24.2 Computation 34.2.1 Outline 34.2.2 Functions used . 34.2.3 Computing the SourceBlackPoint 44.2.4 Computing
8、the DestinationBlackPoint for ICC profiles that are not LUT-based . 44.2.5 Computing the DestinationBlackPoint for ICC profiles that are LUT-based . 54.2.6 Computing the mapping from SourceBlackPoint to DestinationBlackPoint .104.2.7 Applying the black point compensation in a colour conversion 11Ann
9、ex A (informative) Why black point compensation is neccessary 12Bibliography .14 ISO 2015 All rights reserved iiiContents PageBS ISO 18619:2015ISO 18619:2015(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies).
10、 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-
11、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 describe
12、d 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 th
13、e 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
14、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 we
15、ll as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe committee responsible for this document is ISO/TC 130, Graphic technology, in cooperation with the International Color Consortium.iv IS
16、O 2015 All rights reservedBS ISO 18619:2015ISO 18619:2015(E)IntroductionBlack 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. Thi
17、s 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
18、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 particula
19、r 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 vBS ISO 18619:201
20、5BS ISO 18619:2015Image technology colour management Black point compensation1 ScopeThis 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 co
21、lour 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 referencesThe follo
22、wing 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, Imag
23、e technology colour management Architecture, profile format and data structure Part 1: Based on ICC.1:2010ICC.1:2001-04, File Format for Color Profiles3 Terms and definitionsFor the purposes of this document, the terms and definitions given in ISO 15076-1 and the following apply.3.1DestinationBlackP
24、ointcoordinate representing a dark neutral reproducible colour in the destination colour gamut3.2DestinationProfileICC profile, containing the transform from profile connection space to the destination device colour space3.3SourceBlackPointcoordinate representing a dark neutral colour in the source
25、colour gamut3.4SourceProfileICC profile, containing the transform from the source device colour space to the profile connection space3.5RenderingIntentrendering intent of the conversion from a source ICC profiles colour space to a destination ICC profiles colour space3.6LabIdentityProfilereal or vir
26、tual ICC profile that contains a bi-directional (identity) transform between CIELAB and PCSLABINTERNATIONAL STANDARD ISO 18619:2015(E) ISO 2015 All rights reserved 1BS ISO 18619:2015ISO 18619:2015(E)3.7black point compensationBPCcomputational procedure by which a transform between the colour spaces
27、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 space3.8L, a, bL*, a*, or b* component of the CIELAB colour space3.9output-capable CMYK profileCMYK profile containing a transform
28、 from the ICC PCS encoding to the colour space encoding3.10transformmathematical operations that define the change in representation of a colour between two colour spaces3.11gamutrange of colours that a given system is capable of reproducing4 Requirements4.1 ConstraintsThe black point compensation p
29、rocedure 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 compens
30、ation 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
31、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
32、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
33、 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
34、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 reservedBS ISO 18619:2015ISO 18619:2015(E)4.2 Computation4.2.1 OutlineBlack point compensation shall be performed according to the following procedure:a)
35、 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
36、 shall be applied in a colour conversion as specified in 4.2.7.4.2.2 Functions used4.2.2.1 Colour transform with profilesT 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 thaty = T (x,
37、 Profile1, Profile2, Intent) (1)wherex 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 profileD shall denote a function to provide the darkest colour coordinate in the data colour space of Pr
38、ofile for a rendering intent, such thatdc = D (Profile, Intent) (2)wheredc is the darkest colourProfile 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
39、the data colour space of Profile is GrayV shall be the set of (0) (1).If the data colour space of Profile is RGBV shall be the set of (0, 0, 0) (1, 1, 1).If the data colour space of Profile is CMYKV 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
40、 3BS ISO 18619:2015ISO 18619:2015(E)The darkest colour, dc, shall be the lowest value of L* resulting from applying each element v of the appropriate V through the following transform:T (v, Profile, LabIdentityProfile, Intent).NOTE 1 dc is intended to be the value of black or darkest colour in the c
41、olour space of Profile.NOTE 2 Determining the darkest colour in this way works for profiles with both the normal polarity and inverse polarity.4.2.3 Computing the SourceBlackPointThe SourceBlackPoint is computed by first defining LocalBlack of SourceProfile and then using this to compute the SourceB
42、lackPoint.A LocalBlack value for the source colour space shall be defined as follows:If SourceProfile is an output-capable CMYK ICC profileLocalBlack shall be set to T (0, 0, 0), LabIdentityProfile, SourceProfile, Perceptual)If SourceProfile is not an output-capable CMYK ICC profileIf the data colou
43、r space of SourceProfile is CIELAB,LocalBlack shall be set to (0, 0, 0).If the data colour space of SourceProfile is Gray, RGB, or CMYK,LocalBlack shall be set to D (SourceProfile, RenderingIntent).The SourceBlackPoint is then calculated as followsLi shall be set to the L* component of T (LocalBlack
44、, SourceProfile, LabIdentityProfile, RenderingIntent).If Li is greater than 50,SourceBlackPoint shall be set to (50, 0, 0),elseSourceBlackPoint shall be set to (Li, 0, 0).4.2.4 Computing the DestinationBlackPoint for ICC profiles that are not LUT-basedIf DestinationProfile is not LUT-based, then its
45、 DestinationBlackPoint shall be determined as follows:A LocalBlack value for the DestinationProfile data destination colour space shall be determined as follows:LocalBlack shall be set to D (DestinationProfile, RenderingIntent).NOTE Only Gray and RGB are valid data colour spaces for a DestinationPro
46、file that is not LUT-based.The DestinationBlackPoint is then calculated as followsLi shall be set to the L component of T (LocalBlack, DestinationProfile, LabIdentityProfile, RenderingIntent).4 ISO 2015 All rights reservedBS ISO 18619:2015ISO 18619:2015(E)If Li is greater than 50,DestinationBlackPoi
47、nt shall be set to (50, 0, 0),elseDestinationBlackPoint shall be set to (Li, 0, 0).4.2.5 Computing the DestinationBlackPoint for ICC profiles that are LUT-based4.2.5.1 OverviewIf DestinationProfile is LUT-based, then its DestinationBlackPoint shall be determined as follows:InitialLab, inRamp, and ou
48、tRamp shall be calculated as specified in 4.2.5.2.If outRamp is not valid as specified in 4.2.5.3,DestinationBlackPoint shall be set to (0, 0, 0),else if RenderingIntent is RelativeColorimetric, and the outRamp meets the mid range straight test specified in 4.2.5.4,DestinationBlackPoint shall be set
49、 to InitialLab,elseDestinationBlackPoint shall be determined as specified in 4.2.5.5. ISO 2015 All rights reserved 5BS ISO 18619:2015ISO 18619:2015(E)Computing the DestinationBlackPoint(DBP) for prog976iles thatare LUT-based (4.2.5)Computation ofparameters (4.2.5.2)NoNoYesIs outRampvalid?(4.2.5.3)Renderingintent =RelativeColorimetricIs midrangestraight?(4.2.5.4)YesNoYesDBP = InitialLabDetermine DBPusing curve g976itting(4.2.5.5)DBP = (0, 0, 0)Mapping fromSourceBlackPoint toDestinationBlackPoint(4.2.6)Figure 1 DestinationBlackPoint
