1、Graphic technology and photography Colour characterization of digital still cameras (DSCs) Part 3: User controls and readouts for scene-referred imaging applications PD ISO/TR 17321-3:2017 BSI Standards Publication WB11885_BSI_StandardCovs_2013_AW.indd 1 15/05/2013 15:06National foreword This Publis
2、hed Document is the UK implementation of ISO/TR 17321-3:2017. The UK participation in its preparation was entrusted to Technical Committee CPW/42, Photography. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to incl
3、ude all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2017. Published by BSI Standards Limited 2017 ISBN 978 0 580 91997 8 ICS 37.040.10 Compliance with a British Standard cannot confer immunity from legal obligations. Th
4、is Published Document was published under the authority of the Standards Policy and Strategy Committee on 30 April 2017. Amendments/corrigenda issued since publication Date Text affected PUBLISHED DOCUMENT PD ISO/TR 17321-3:2017 ISO 2017 Graphic technology and photography Colour characterization of
5、digital still cameras (DSCs) Part 3: User controls and readouts for scene- referred imaging applications Technologie graphique et photographie Caractrisation de la couleur des appareils photonumriques Partie 3: Contrles utilisateur et lectures pour les applications dimagerie par scne TECHNICAL REPOR
6、T ISO/TR 17321-3 Reference number ISO/TR 17321-3:2017(E) First edition 2017-04 ISO/TR 17321-3:2017(E)ii ISO 2017 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2017, Published in Switzerland All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utili
7、zed 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 ISOs member body in the country of the requester. ISO copyrigh
8、t office Ch. de Blandonnet 8 CP 401 CH-1214 Vernier, Geneva, Switzerland Tel. +41 22 749 01 11 Fax +41 22 749 09 47 copyrightiso.org www.iso.org ISO/TR 17321-3:2017(E)Foreword iv Introduction v 1 Scope . 1 2 Normative references 1 3 T erms and definitions . 1 4 Design of scene-referred (SR) capture
9、processing mode . 1 4.1 General . 1 4.2 Processing aims 1 4.3 Colour encoding and file format 1 4.4 User readouts . 2 4.5 Indication of SR mode . 2 4.6 Guideline for raw processor 2 Annex A (informative) Guidelines for capture using scene-referred (SR) capture processing mode . 3 Bibliography 5 ISO
10、2017 All rights reserved iii Contents Page PD ISO/TR 17321-3:2017 ISO/TR 17321-3:2017(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
11、 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 col
12、laborates 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 appr
13、oval 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. www .iso .org/ directives Attention is drawn to the possibility that some of the elements of this document may be the sub
14、ject 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. www .iso .org/ patents Any trade
15、name used in this document is information given for the convenience of users and does not constitute an endorsement. For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherenc
16、e to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see the following URL: h t t p :/ www .iso .org/ iso/ foreword .html This document was prepared by Technical committee ISO/TC 42, Photography. A list of all the parts in the ISO 17321 series can be found on
17、the ISO website.iv ISO 2017 All rights reserved PD ISO/TR 17321-3:2017 ISO/TR 17321-3:2017(E) Introduction Pictorial photography by and large produces images that convey the specific artistic intent of the photographer. The intent might convey a complex artistic vision, or it might simply attempt to
18、 create images that are generally pleasing to viewers. Other types of photography, such as the reproduction of images of artworks and other objects for archival purposes and the reproduction of images for scientific measurement and analysis, reproduce images that require an accurate representation o
19、f the scene captured, where accuracy is measured in terms of relative colourimetry or adapted relative colourimetry (for cases where viewer adaptation differs when looking at the correctly reproduced image and when looking at the actual scene). Images for pictorial photography are typically processe
20、d with an output-referred representation on some medium. In the case of film, the medium is often a photographic print or transparency. In the case of digital capture, the output characteristics are specified and communicated either by the identification of a standard reference medium, such as sRGB
21、or ROMM RGB, or by the inclusion of an output-intent ICC profile. Output-referred images are often not colourimetrically accurate photographic reproductions of the actual scene or object because scenes vary widely in their highlight-to-midtone and midtone-to-shadow luminance rations, in their colour
22、 gamuts, and in other characteristics, output media vary widely in their colour gamuts and their luminance range capabilities, and pictorial photographers choose output media whose characteristics complement their artistic intent. While scene-referred (SR) images, that is, colourimetrically accurate
23、 images of scenes and objects, are required, it is difficult to obtain colourimetrically accurate images of scenes and objects. Digital archiving facilities sometimes use targets to create ICC profiles to invert the colour processing from output-referred images to scene-referred images. This approac
24、h is commonly used, but it has significant drawbacks: a) characterization charts do not always represent the actual spectra to be captured; b) the camera colour processing and chart used can limit the colour gamut and dynamic range of the resulting scene-referred images; c) precise exposure control
25、is difficult because the camera and image readouts typically reflect the state of the image prior to application of the ICC profile; d) some cameras employ colour processing that is image dependent when producing output- referred images. In this last case the ICC profile determined with the chart is
26、 only likely to be accurate when photographing the chart itself. It is also possible to obtain scene-referred images by converting camera raw images using camera raw processing software. This approach is technically more sound than creating scene-referred images from output-referred images, but ther
27、e are still issues: commercial camera raw processing tends to be focused on creating output-referred images; open-source software tends to be complex; additional software is often needed to convert the scene-referred image data to standard scene- referred colour encodings. Users need simple and clea
28、r camera and camera raw processing controls and readouts that allow them to easily produce quality scene-referred images in appropriate encodings. ISO 2017 All rights reserved v PD ISO/TR 17321-3:2017 ISO/TR 17321-3:2017(E) This document describes a scene-referred (SR) capture-processing mode that c
29、ould be added to digital still cameras for use by those photographers interested in colourimetrically accurate images of scenes and objects.vi ISO 2017 All rights reserved PD ISO/TR 17321-3:2017 TECHNICAL REPORT ISO/TR 17321-3:2017(E) Graphic technology and photography Colour characterization of dig
30、ital still cameras (DSCs) Part 3: User controls and readouts for scene-referred imaging applications 1 Scope This document provides guidelines for user controls and readouts employed in scene-referred capture processing modes implemented in digital cameras and camera raw processing software. 2 Norma
31、tive references There are no normative references in this document. 3 T erms a nd definiti ons No terms and definitions are listed in this document. ISO and IEC maintain terminological databases for use in standardization at the following addresses: ISO Online browsing platform: available at h t t p
32、 :/ www .iso .org/ obp IEC Electropedia: available at h t t p :/ www .electropedia .org/ 4 Design of scene-referred (SR) capture processing mode 4.1 General The SR capture processing mode is intended for applications where the objective is to produce images that represent colourimetrically accurate
33、colours of the scene captured. When using the SR mode it is best if the capture conditions such as the scene illumination geometry and spectral characteristics of the illumination are controlled by the user, such as in a studio or reprographic setup. The SR mode is not specifically intended for gene
34、ral pictorial photography. See Annex A for additional information. 4.2 Processing aims The aim of the colour processing applied is to produce accurate scene colourimetry, with the scene adopted white adapted to the image encoding adopted white as described in ISO/TR 17321-2. ISO 17321-1 specifies ca
35、mera characterization metrology. ISO/TR 17321-2 provides considerations for determining scene analysis transforms. 4.3 C olour enc oding and file format In the SR capture processing mode, the colour encoding used for the images is a scene-referred encoding, such as the scRGB colour encoding specifie
36、d in IEC 61966-2-2, or the RIMM RGB encoding specified in ISO/TS 22028-3. It is important that most colours of interest in the scene are within the colour gamut and dynamic range of the encoding selected. The encoding selected is communicated by the file format used, for example by embedding an ICC
37、profile. ISO 2017 All rights reserved 1 PD ISO/TR 17321-3:2017 ISO/TR 17321-3:2017(E) 4.4 User readouts A CIE L* (L*) histogram of the image is presented to the user, that is, the scene-referred image values are converted to L* values and displayed in the histogram. L* values are displayed from “0”
38、to “over 100”. Preferably, main markers are placed at L* = 0, 50 and 100, with sub markers at every L* = 5 values (see Figure 1). It is also useful to display image values above diffuse white, extending L* values above L* = 100 based on the colour encoding and file format used (see Figure 1). NOTE V
39、alues over L* = 100 are utilized in this document, but it does not address the degree to which L* is perceptually uniform. Key 1 diffuse white threshold-(L*=95) 2 headroom-(based on encoding headroom) 3 histogram display 4 scene adopted white chromaticity reference (L*=95) Figure 1 Example of histog
40、ram frame 4.5 Indication of SR mode It is desired that the SR mode is clearly indicated by words such as “scene-referred” or “SR” on the appropriate camera mode control, in the camera menu, or in the camera raw processing software user interface. It is important that the user be aware when they are
41、in a scene-referred mode and when they are not. 4.6 Guideline for raw processor In the SR mode, the raw processor converts raw files to scene referred image files. The colour rendering is disabled and scene-referred encodings as defined in ISO 22028-1 are used for the processed images. The raw proce
42、ssor offers the option to use recorded scene adopted white (exposure and white balance) information.2 ISO 2017 All rights reserved PD ISO/TR 17321-3:2017 ISO/TR 17321-3:2017(E) Annex A (informative) Guidelines for capture using scene-referred (SR) capture processing mode A.1 Guideline for proper ill
43、umination of artwork reproduction/archives The proper illumination for two-dimensional artwork is the uniform illumination produced by light sources placed at an angle of incidence of 30 to 45. Lens flare can negatively impact image quality. Use of a lens shade and minimizing unwanted light reflecti
44、on in the scene is helpful. NOTE 1 If the imaging system incorporates lens fall-off corrections or flat fielding these corrections can be applied to improve image uniformity. NOTE 2 The light sources used for capture are supported by the camera or camera raw processing software. In other words, the
45、camera or camera raw processing software produces colourimetrically accurate scene-referred images with the light sources used. For this to happen, it is important to consider the spectral power distribution of the light sources. A.2 Guideline for setting the white balance It is desirable that users
46、 have the ability to set the white balance. The following two approaches are used: Method 1: use of a full frame reference target to set the white balance (custom white balance). Method 2: use of a user selection tool to define a specific region in an image preview to be used for setting the-white b
47、alance (custom white reference - can be used in conjunction with the same target used for exposure described in A.3). Typically, the specific circumstances determine which of the above methods are preferred. A.3 Guideline for proper exposure setting Exposure is set using a reflective chart comprised
48、 of equally spaced in L*, spectrally neutral semi- gloss and additional (optional) gloss black patches (see Figure A.1), and comparing the known chart patch L* values to direct readout of captured scene L* values. The camera is adjusted so that the L* = 95 white patch produces a scene-referred image
49、 value of L* = 95, this step also being used to set the white balance. In some cases it is desirable to set the exposure based on the midtone L* = 50 patch, as many cameras and exposure metres are designed to set exposure based on a midtone. ISO 2017 All rights reserved 3 PD ISO/TR 17321-3:2017 ISO/TR 17321-3:2017(E) Key 1 semi-gloss values (L*= 5 to L*= 95) 2 gloss black (L*=4) 3 measurement scale, in millimetres 4 perceptual middle value (L*=50) F i g u r e A . 1 I l l u s t r a t i o n o f r e f l e
