ISO/TR 17321-3:2017

TECHNICAL ISO/TR
REPORT 17321-3
First edition
2017-04
Graphic technology and
photography — Colour
characterization of digital still
cameras (DSCs) —
Part 3:
User controls and readouts for scene-
referred imaging applications
Technologie graphique et photographie — Caractérisation de la
couleur des appareils photonumériques —
Partie 3: Contrôles utilisateur et lectures pour les applications
d’imagerie par scène
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Design of scene-referred (SR) capture 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
Foreword
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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. www .iso .org/ directives
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URL: http:// 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 the ISO website.
iv © ISO 2017 – All rights reserved

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 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 of
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 processed 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 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 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 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 approach 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 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 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 there 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 clear camera
...