SIST ISO 17321-1:2011

INTERNATIONAL ISO
STANDARD 17321-1
First edition
2006-12-01
Graphic technology and photography —
Colour characterisation of digital still
cameras (DSCs) —
Part 1:
Stimuli, metrology and test procedures
Technologie graphique et photographie — Caractérisation de la couleur
des appareils photonumériques —
Partie 1: Stimuli, métrologie et modes opératoires d'essai

Reference number
©
ISO 2006
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ii © ISO 2006 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 DSC colour characterization methods. 2
4.1 General. 2
4.2 Spectral sensitivity-based characterization — Method A. 3
4.3 Target-based characterization — Method B. 4
Annex A (informative) Recommended laboratory set-up for photographing a reflection colour test
target . 8
Annex B (informative) Digital still camera / sensitivity metamerism index (DSC/SMI) . 10
Annex C (informative) Characterization target considerations . 15
Annex D (informative) Calculating natural scene element responses from spectral
characterization data. 22
Bibliography . 25

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 17321-1 was prepared by Technical Committee ISO/TC 42, Photography in collaboration with
ISO/TC 130, Graphic technology.
ISO 17321 consists of the following parts, under the general title Graphic technology and photography —
Colour characterization of digital still cameras (DSCs):
⎯ Part 1: Stimuli, metrology and test procedures

iv © ISO 2006 – All rights reserved

Introduction
The spectral responses of the colour analysis channels of digital still cameras (DSCs) do not, in general,
match those of a typical human observer, such as defined by the CIE standard colorimetric observer. Nor do
the responses of different DSCs ordinarily match each other. In characterizing DSCs, it is therefore necessary
to take account of the DSC spectral sensitivities, illumination, and encoding colour space. This part of
ISO 17321 will begin to address these considerations. This part of ISO 17321 defines stimuli (spectral
illumination or a colour target), metrology and photographic test procedures for acquiring DSC
characterization data. It specifies test procedures for “scenes”, the most general picture taking conditions
where metameric colours and a range of illumination sources are encountered. It also specifies test
procedures for hardcopy “originals”, a more narrowly defined picture-taking condition in which the illumination
source and the colorants being imaged are pre-defined.
The ISO 17321 series will distinguish among several possible image representations in different colour
encodings as depicted in Figure 1 which shows the diagram of a generic image workflow for digital
photography.
Figure 1 — Generic image workflow for digital photography
The DSC characterizations obtained using this part of the ISO 17321 will be applicable to raw (sensor-
referred) DSC data. Two alternative methods are described for obtaining these characterization data.
Method A, the spectral method, uses spectral lights as stimuli for measuring the colour performance of a DSC.
Method B, the target method, involves the use of a physical colour test target under specific lighting conditions
to measure DSC colour performance. Annexes A to C recommend a laboratory set-up for photographing
reflection targets, provide target patch selection criteria, and provide a digital still camera metamerism index.
Some operations (colour pixel reconstruction, flare removal, white balancing) can be performed without
disqualifying the DSC data as being raw. However, operations that render the image data so that they become
output-referred (ready to display or to print) generally do disqualify the data. With such cameras, this standard
can only be applied if the capability exists to extract or to regenerate raw data, e.g. by applying the inverse of
the rendering transform or by tapping the appropriate signals internal to the camera.
The technical experts who have developed this part of ISO 17321 recognize that a standard that could be
applied generally to any (not just raw) DSC output would be desirable. Such a standard is problematic for
DSCs that employ colour-rendering algorithms in order to produce output-referred image data. For such DSCs,
it would frequently be impossible to determine if colour analysis errors relative to the scene or original
captured were due to sensor image encoding errors or to proprietary colour rendering algorithms. The only
way to make this distinction is if the colour rendering used is well documented and available, and the rendered
data can be converted to un-rendered data by inverting the colour rendering. This situation is unlikely to occur
because one of the major differentiators in DSC performance is the colour rendering. Sophisticated colour-
rendering algorithms can be image dependent, and locally varying within an image. This makes it extremely
difficult to reliably determine the exact colour rendering used by analysing captured test scenes.
The purpose of this part of ISO 17321 is both to assist in the characterization of DSCs for colour management
purposes and to assist camera manufacturers in the determination of the colour analysis capabilities of DSCs
that they are developing. This standard is applicable to any DSC intended for photographic or graphic
technology applications. However, for many users it is not practical to apply this part of ISO 17321 to
individual DSCs. Some of the measurements described in this part of ISO 17321 require complex, expensive
measurement equipment. In the case of test targets that are commercially produced, spectral as well as
colorimetric measurement data would ideally accompany the target.
Those unfamiliar with this part of ISO 17321 are encouraged to read through the entire standard (in particular
the informative annexes) before proceeding with DSC characterization, in order to verify appropriateness for
their particular application. In some cases, the procedures described in the multimedia standard,
[5]
IEC 61966-9 might be more applicable.
It is proposed that other parts of ISO 17321 will be developed in the future to deal with other aspects of the
colour characterization of digital still cameras.

vi © ISO 2006 – All rights reserved

INTERNATIONAL STANDARD ISO 17321-1:2006(E)

Graphic technology and photography — Colour
characterisation of digital still cameras (DSCs) —
Part 1:
Stimuli, metrology and test procedures
1 Scope
This part of ISO 17321 specifies colour stimuli, metrology, and test procedures for the colour characterization
of a digital still camera (DSC) to be used for photography and graphic technology. Two methods are provided,
one using narrow spectral band illumination and the other using a spectrally and colorimetrically calibrated
target. Except for a specific set of permitted data operations, these DSC data are raw.
This part of ISO 17321 does not specify the methods for deriving transformations from raw DSC data in order
to estimate scene colorimetry.
2 Normative references
The following referenced documents are indispensable for the application 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 7589:2002, Photography — Illuminants for sensitometry — Specifications for daylight, incandescent
tungsten and printer
ISO 13655:1996, Graphic technology — Spectral measurement and colorimetric computation for graphic arts
images
ISO 14524:1999, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
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 The adopted white can vary within a scene.
NOTE 2 No assumptions can be made concerning the relation between the adapted or adopted white and
measurements of near perfectly reflecting diffusers in a scene, because measurements of such diffusers will depend on
the illumination and viewing geometry, and other elements in the scene that can affect perception.
[ISO 22028-1]
3.2
digital still camera
DSC
device that incorporates an image sensor and that produces a digital signal representing a still picture
NOTE A digital still camera is typically a portable, hand-held device. The digital signal is usually recorded on a
removable memory, such as a solid-state memory card or magnetic disk.
3.3
opto-electronic conversion function
OECF
relationship between log of input levels and corresponding digital output levels for an opto-electronic digital
image capture system
NOTE If the input log exposure points are very finely spaced and the output noise is small compared to the
quantization interval, the OECF possibly has a step-like character. Such behaviour is an artefact of the quantization
process and needs to be removed by using an appropriate smoothing algorithm or by fitting a smooth curve to the data.
3.4
raw DSC image data
image data produced by, or internal to, a DSC that has not been processed, except for A/D conversion and
the following optional steps:
⎯ linearization,
⎯ dark current/frame subtraction,
⎯ shading and sensitivity (flat field) correction,
⎯ flare removal,
⎯ white balancing (e.g. so the adopted white produces equal RGB values or no chrominance),
⎯ missing colour pixel reconstruction (without colour transformations).
3.5
spectrally non-selective
exhibiting reflective or transmissive characteristics that are constant over the wavelength range of interest
4 DSC colour characterization
...