ISO/TS 19264-1:2017

Photography - Archiving systems - Image quality analysis - Part 1: Reflective originals

ISO/TS 19264-1:2017 describes a method for analysing imaging systems quality in the area of cultural heritage imaging. The method described analyses multiple imaging systems quality characteristics from a single image of a specified test target. The specification states which characteristics are measured, how they are measured, and how the results of the analysis need to be presented. ISO/TS 19264-1:2017 applies to scanners and digital cameras used for digitization of cultural heritage material. NOTE This document addresses imaging of reflective originals, a future part two will address imaging of transparent originals.

Photographie — Systèmes d'archivage — Analyse de la qualité d'image — Partie 1: Documents réfléchissants

General Information

• Status: Withdrawn
• Publication Date: 24-Apr-2017
• Withdrawal Date: 24-Apr-2017
• ICS: 01.140.20 - Information sciences
• ICS: 37.040.01 - Photography in general
• Technical Committee: ISO/TC 42 - Photography
• Drafting Committee: ISO/TC 42/JWG 26 - Joint ISO/TC 42-TC 46/SC 11-TC 171 WG: Imaging system capability qualification for archival recording and approval
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 10-Jun-2021
• Completion Date: 13-Dec-2025

Relations

• Revised: ISO 19264-1:2021 - Photography - Archiving systems - Imaging systems quality analysis - Part 1: Reflective originals
• Effective Date: 23-Apr-2020

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 19264-1
First edition
2017-04
Corrected version
2018-05
Photography — Archiving systems —
Image quality analysis —
Part 1:
Reflective originals
Photographie — Systèmes d'archivage — Analyse de la qualité
d'image —
Partie 1: Documents réfléchissants
Reference number
©
ISO 2017
© ISO 2017
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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 System setup and calibration .10
4.1 General .10
4.2 System configuration .10
4.3 Camera/scanner settings .10
4.4 Exposure .10
4.5 White balancing .11
4.6 ICC Profiling .11
4.7 Focusing .11
4.8 Colour encoding .11
4.9 Reproduction scale .12
5 Imaging system quality analysis procedure .12
6 Imaging systems quality characteristics and metrics .13
6.1 General .13
6.2 Tones and noise .13
6.3 Colour .16
6.4 Details .18
6.5 Geometry .20
7 Reporting results .21
7.1 General .21
7.2 Example report for tone reproduction results .22
7.3 Gain modulation .23
7.4 Dynamic range.24
7.5 Noise .24
7.6 Banding .26
7.7 Defect pixels .27
7.8 White balance.27
7.9 Colour reproduction .28
7.10 Colour mis-registration .29
7.11 Sampling rate.29
7.12 Resolution .29
7.13 MTF 50/MTF 10 .29
7.14 Sharpening .29
7.15 Acutance .29
7.16 Illuminance non-uniformity .29
7.17 Chrominance non-uniformity .29
7.18 Distortion .29
7.19 Reproduction scale .29
Annex A (normative) Test chart requirements .30
Annex B (normative) Guidelines for imaging performance aims and tolerances .32
Annex C (informative) Example of multi-pattern chart: Universal Test Target (UTT) .34
Bibliography .55
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. 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. 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 World Trade Organization (WTO)
principles in the Technical Barriers to Trade (TBT), see the following URL: http: //www .iso
.org/iso/foreword .html
The committee responsible for this document is ISO/TC 42, Photography.
This corrected version of ISO/TS 19264-1:2017 incorporates the following correction:
— In 6.3, the “+” sign between the two rootsquare elements of the formula was corrected back to a
“−“ sign.
iv © ISO 2017 – All rights reserved

Introduction
Electronic imaging systems, such as scanners and cameras, can be used for digitizing physical records,
e.g. documents, pictures, maps. The resulting digital images can be more or less accurate in terms of how
well they reproduce the original record’s tones, colours, details, etc. These and other characteristics of
a digital image can be assessed by imaging systems quality analysis. In general, the achievable accuracy
of digital reproductions depends on the nature of the original record and the digitization, especially the
performance of the imaging system and the applied system settings.
In some organizations, e.g. within the archiving and cultural heritage field, where considerable
resources are put into digitization projects, it is key to ensure that the required imaging systems
quality is met and that it is consistent. To this end, imaging systems quality analysis can assist those
developing or acquiring imaging systems with the assessment and verification of system performance,
such as the specified resolution and dynamic range of a scanner, and the comparative performance of
different imaging systems. Imaging systems quality analysis is also used for setting up and calibrating
imaging systems as well as for enhancing their performance. Finally, imaging systems quality analysis
is used for assessing accuracy and controlling imaging consistency over time. Note, that while the
need to ensure imaging systems quality is generic, the required level of imaging systems quality and
accuracy is use-case specific. For example, when digitizing watercolours it is usually essential to reach
a high degree of accuracy in the capture of the colour information, while this is not normally equally
critical when digitizing newspapers. Also, some image processing programs, such as Optical Character
Recognition (OCR), are more accurate if the contrast is enhanced during imaging.
In practice, imaging systems quality is analysed by digitizing a physical reference target (test chart)
with known (measured) values and comparing these reference values to the corresponding captured
values represented in the digital image file (see Figure 1).
The use of a test chart ensures that the imaging systems quality characteristics can be determined
objectively. However, to be usable the quality of the target needs to exceed the performance of the
imaging system. For example, to determine the resolution of an imaging system, the target needs to
have a technical pattern with more details than the system is capable of resolving. Imaging systems
quality analysis reports how accurately the imaging system reproduces the reference target. Therefore,
if the original record differs significantly from the target, e.g. with respect to tone, tonal range, colours,
details, and light reflectance/absorbance, this may, in spite of a well performing system, compromise
the accuracy of the reproduced image. See also References [25] and [26]. Ideally, the targets should
resemble the nature of the original material. However, given the many different types of original records
this is often not practical or technically impossible. Even though systems may perform differently
on the different types of originals this document provides tools to verify if a system is accurately
calibrated and in general performs well on a selected type of original. This is sufficient in most cases
because systems are usually designed to handle various types of originals (being close to the Luther
condition) Performance on specific types of originals however can only be verified if the tools are made
of that material. It is also important to note that an accurate reproduction usually requires subsequent
processing to render a visually pleasing image.
There are ISO standards for objectively measuring different performance characteristics of imaging
systems, e.g. resolution, noise, dynamic range, tone and colour reproduction (see Clause 2). This
document combines all of the standards that relate to the imaging systems quality analysis for cultural
heritage and defines a tool set to apply them to these devices and workflows. These tools are based
on the use of a test chart with multiple technical patterns coupled with software that allows the user
to analyse several imaging systems quality characteristics simultaneously and receive comprehensive
results. However, these tools are not based on a standardized image quality analysis method, which
has caused confusion among users. With the publication of this specification imaging systems quality
analysis tools can refer to an ISO document.
To support this document a standard with a glossary including all relevant terms and definitions
has been developed (ISO 19262). Further this document is accompanied by a Technical Report (ISO/
TR 19263-1) that provides practical guidance on how to use this document.
TECHNICAL SPECIFICATION ISO/TS 19264-1:2017(E)
Photography — Archiving systems — Image quality
analysis —
Part 1:
Reflective originals
1 Scope
This document describes a method for analysing imaging systems quality in the area of cultural heritage
imaging. The method described analyses multiple imaging systems quality characteristics from a single
image of a specified test target. The specification states which characteristics are measured, how they
are measured, and how the results of the analysis need to be presented.
This specification applies to scanners and digital cameras used for digitization of cultural heritage
material.
NOTE This document addresses imaging of reflective originals, a future part two will address imaging of
transparent originals.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 12233, Photography — Electronic still picture imaging — Resolution and spatial frequency responses
ISO 14524, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs)
ISO 15739, Photography — Electronic still-picture imaging — Noise measurements
ISO 16067-1, Photography — Spatial resolution measurements of electronic scanners for photographic
images — Part 1: Scanners for reflective media
ISO 17957, Photography — Digital cameras — Shading measurements
ISO 21550, Photography — Electronic scanners for photographic images — Dynamic range measurements
CIE 15, Colorimetry
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
acutance
numerical value that correlates to some extent with subjective image sharpness
[SOURCE: ISO 19262:2015, 3.1]
3.2
Adobe RGB 1998
three-component colour image encoding defined in Adobe RGB (1998) colour image encoding
Note 1 to entry: Adobe RGB 1998 Colour Image Encoding can be found under the following URL https: //www
.adobe .com/digitalimag/pdfs/AdobeRGB1998 .pdf
[SOURCE: ISO 12640-4:2011, 3.1, modified — addition of the Note 1 to entry.]
3.3
banding
imaging
unwanted stripes or bands that occur in a digital image
Note 1 to entry: Note1 to entry: Bands are usually caused by fixed pattern noise of sensors in scanners,
interference problems between electronic parts of a camera, or by too-coarse quantization.
[SOURCE: ISO 19262:2015, 3.9, modified — addition of “or by too-coarse quantization” in the Note 1
to entry.]
3.4
checkerboard
regular squared dark and bright structure on a surface like the one used on a chess board
[SOURCE: ISO 19262:2015, 3.18]
3.5
chroma, C*
chromatic
chromaticness, colourfulness, of an area judged as a proportion of the brightness of a similarly
illuminated area that appears white or highly transmitting
[SOURCE: ISO/IEC 8613-2:1995, 3.18]
3.6
CIELAB colour space
three-dimensional, approximately uniform colour space, produced by plotting, in rectangular
coordinates L*, a*, b*
Note 1 to entry: This colour space has been designed to be device independent.
[SOURCE: CIE Publication 15 and ISO/IEC 5631-1:2015, 3.6, modified — Note 1 to entry has been
modified.]
3.7
colour
sensation resulting from the visual perception of radiation of a given spectral composition
[SOURCE: ISO 4618:2014, 2.58, modified — definition slightly changed and Note 1 and Note 2 to entry
have been deleted.]
3.8
colour difference
distinction between two colours observed or measured under standard conditions
[SOURCE: ISO 12637-2:2008, 2.21]
2 © ISO 2017 – All rights reserved

3.9
colour encoding
generic term for a quantized digital encoding of a colour space, encompassing both colour space
encodings and colour image encodings
[SOURCE: ISO/TS 22028-3:2012, 3.6]
3.10
colour misregistration
colour-to-colour spatial dislocation of otherwise spatially coincident colour features of an imaged object
[SOURCE: ISO 19262:2015, 3.42]
3.11
contrast
difference between the grey levels of two specified parts of the image
[SOURCE: ISO 21227-1:2003, 3.5.3]
3.12
pixel defect
pixel or subpixel that operates in a way other than the one in which it is driven
[SOURCE: ISO 9241-302:2008, 3.4.30]
3.13
ΔE
see colour difference
[SOURCE: ISO 19262:2015, 3.63]
3.14
digital image
digital file consisting of picture elements (pixels) with one or more digital code values per pixel that
represent a colour or tonal value
[SOURCE: ISO 19262:2015, 3.73, modified — deletion of the Note 1 to entry.]
3.15
digital imaging
process of creating digital images
Note 1 to entry: The term can also be used more generally to include digital image processing.
[SOURCE: ISO 19262:2015, 3.74]
3.16
digital imaging system
system that records and/or produces images using digital data
[SOURCE: ISO 12231:2012, 3.38]
3.17
digital still camera
DSC
device which incorporates an image sensor and produces a digital signal representing a still picture
Note 1 to entry: 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.
[SOURCE: ISO 12231:2012, 3.40]
3.18
digitization
act of generating a digital (quantized) representation of a continuous signal
[SOURCE: ISO 20998-1:2006, 2.7, modified — Tne Note 1 to entry has been deleted.]
3.19
distortion
geometric distortion
displacement from the ideal shape of a subject (lying on a plane parallel to the image plane) in the
recorded image
Note 1 to entry: It basically derives from variation of lateral magnification in the image field of a camera lens
and results in straight lines being rendered as curves. There are other factors to induce geometric distortion, for
example rotational asymmetricity of a camera lens or position shift processing in a camera imaging process.
[SOURCE: ISO 19262:2015, 3.82]
3.20
dynamic range
difference, over a given luminance range, between maximum and minimum signal levels, expressed in
decibels, contrast ratios or f-stops
Note 1 to entry: The minimum signal level needs to be greater than a specified usable signal level.
Note 2 to entry: This definition is derived from IEC 702–04–23 but was altered to match the imaging and
archiving application.
[SOURCE: ISO 19262:2015, 3.87]
3.20.1
ISO DSC dynamic range
ratio of the maximum luminance level that appears unclipped to the minimum luminance level that can
be reproduced with an incremental signal-to-temporal-noise ratio of at least 1, as determined according
to ISO 15739
[SOURCE: ISO 12231:2012, 3.86]
3.20.2
ISO scanner dynamic range
difference of the maximum density where the incremental gain is higher than 0,5, as determined
according to ISO 21550 to the minimum density that appears unclipped
[SOURCE: ISO 21550:2004, 3.13]
3.21
exposure
H
total quantity of light allowed to fall upon a photosensitive emulsion or an imaging sensor
Note 1 to entry: The exposure is measured in lux per second.
[SOURCE: ISO 10934-1:2002, 2.50, modified — A symbol, the field of application and a note to entry
have been added.]
3.22
fast scan direction
scan direction corresponding to the direction of the alignment of the addressable photoelements in a
linear array image sensor
[SOURCE: ISO 16067-1:2003, 3.7]
4 © ISO 2017 – All rights reserved

3.23
gain modulation
variation of the gain over the signal level
Note 1 to entry: One example for a gain modulation is the application of a gamma to an image.
[SOURCE: ISO 19262:2015, 3.109]
3.24
gray scale
grey scale pattern
test chart consisting of test pattern based on spectrally neutral or effectively spectrally neutral, and
consists of a large number of different reflectance or transmittance values in a prescribed spatial
arrangement
Note 1 to entry: Grey scale patterns are typically used to measure opto-electronic conversion functions.
3.25
horizontal resolution
resolution value measured in the longer image dimension, corresponding to the horizontal direction for
a “landscape” image orientation, typically using a vertically oriented test-chart feature
[SOURCE: ISO 12231:2012, 3.65]
3.26
ICC profile
International Colour Consortium’s file format, used to store transforms from one colour encoding
to another, e.g. from device colour coordinates to profile connection space, as part of a colour
management system
[SOURCE: ISO 22028-1:2016, 3.24]
3.27
image quality
impression of the overall merit or excellence of an image, as perceived by an observer neither associated
with the act of photography, nor closely involved with the subject matter depicted
Note 1 to entry: The purpose of defining image quality in terms of third-party (uninvolved) observers is to
eliminate sources of variability that arise from more idiosyncratic aspects of image perception and pertain to
attributes outside the control of imaging system designers.
[SOURCE: ISO 20462-1:2005, 3.5]
3.28
limiting resolution
value of that portion of a specified resolution test pattern, measured in line widths per picture
height, which corresponds to an average modulation value equal to some specified percentage of the
modulation value at a specified reference frequency
Note 1 to entry: The limiting resolution could be the test pattern value, in line widths per picture height (w /h ),
l p
corresponding to a camera output modulation level of 10 % of the camera output modulation level at a reference
frequency of 10 w /h .
l p
3.29
maximum modulation
maximum value of the spatial frequency response
Note 1 to entry: Maximum modulation is an indicator for applied sharpening.
3.30
modulation
difference between the minimum and maximum signal levels divided by the sum of these levels
[SOURCE: ISO/IEC 29112:2012, 3.17]
3.31
noise
unwanted variations in the response of an imaging system
[SOURCE: ISO 15739:2013, 3.9]
3.32
opto-electronic conversion function
OECF
relationship between the log of the input levels and the corresponding digital output levels for an opto-
electronic digital image capture system
Note 1 to entry: 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.
[SOURCE: ISO 17321-1:2012, 3.3]
3.33
original-referred image state
scene-referred
image state associated with image data that represents the colour-space coordinates of the elements of
a two dimensional hardcopy or softcopy image, typically produced by scanning artwork, photographic
transparencies or prints, or photomechanical or other reproductions
Note 1 to entry: When the phrase “original-referred” is used as a qualifier to an object, it implies that the object
is in an original-referred image state. For example, original-referred image data are image data in an original-
referred image state.
Note 2 to entry: Original-referred image data are related to the colour-space coordinates of the original, typically
measured according to ISO 13655, and do not include any additional veiling glare or other flare.
Note 3 to entry: The characteristics of original-referred image data that most generally distinguish them from
scene-referred image data are that they refer to a two-dimensional surface, and the illumination incident on the
two-dimensional surface is assumed to be uniform (or the image data corrected for any non-uniformity in the
illumination).
Note 4 to entry: There are classes of originals that produce original-referred image data with different
characteristics. Examples include various types of artwork, photographic prints, photographic transparencies,
emissive displays, etc. When selecting a colour re-rendering algorithm, it is usually necessary to know the class of
the original in order to determine the appropriate colour re-rendering to be applied. For example, a colourimetric
intent is generally applied to artwork, while different perceptual algorithms are applied to produce photographic
prints from transparencies, or newsprint reproductions from photographic prints. In some cases the assumed
viewing conditions are also different between the original classes, such as between photographic prints and
transparencies, and will usually be considered in well-designed systems.
Note 5 to entry: In a few cases, it can be desirable to introduce slight colourimetric errors in the production of
original-referred image data, for example to make the gamut of the original more closely fit the colour space, or
because of the way the image data were captured (such as a Status A densitometry-based scanner).
[SOURCE: ISO 22028-1:2016, 3.32, modified — A term has been slightly modified and second one added.]
6 © ISO 2017 – All rights reserved

3.34
output-referred image state
image state associated with image data that represents the colour-space coordinates of the elements of
an image that has undergone colour-rendering appropriate for a specified real or virtual output device
and viewing conditions
Note 1 to entry: When the phrase “output-referred” is used as a qualifier to an object, it implies that the object is
in an output-referred image state. For example, output-referred image data are image data in an output-referred
image state.
Note 2 to entry: Output-referred image data are referred to the specified output device and viewing conditions. A
single scene can be colour-rendered to a variety of output-referred representations depending on the anticipated
output-viewing conditions, media limitations, and/or artistic intents.
Note 3 to entry: Output-referred image data can become the starting point for a subsequent reproduction process.
For example, sRGB output-referred image data are frequently considered to be the starting point for the colour
re-rendering performed by a printer designed to receive sRGB image data.
[SOURCE: ISO/TS 22028-3:2012, 3.16]
3.35
profiling
creation of (ICC) colour profiles for imaging devices in order to enhance the accuracy in colour
reproduction
[SOURCE: ISO 19262:2015, 3.197]
3.36
quality assurance
all those planned and systematic activities necessary to provide confidence that a product satisfies
given acceptance criteria
[SOURCE: ISO 22716:2007, 2.27]
3.37
quality control
part of quality management focused on fulfilling quality requirements
[SOURCE: ISO 9000:2015, 3.3.7]
3.38
reference target
arrangement of test patterns designed to test particular aspects of an imaging system
Note 1 to entry: See examples in ISO 12233:2017, ISO 16067-1 and ISO 16067-2.
[SOURCE: ISO 19262:2015, 3.207]
3.39
reproduction scale
ratio of the size of an object in a digital image and the size of the original object
[SOURCE: ISO 19262:2015, 3.215]
3.40
reprographic illumination geometry
typical arrangement of the illumination in two dimensional reprographic photography where the lights
are positioned on two sides of the original in a 45° angle to the plane of original and to the camera,
which is positioned perpendicular to the plane of the original
[SOURCE: ISO 19262:2015, 3.216]
3.41
resolution
theoretical resolution
limiting resolution
measure of the ability of a camera system, or a component of a camera system, to depict picture detail
Note 1 to entry: Resolution measurement metrics include resolving power, limiting resolution, special frequency
response (SFR), MTF and OTF.
[SOURCE: ISO 12233:2017, 3.22, modified — Two new terms and a Note 1 to entry have been added.]
3.42
RGB
additive process colour model where the channels are called Red, Green and Blue
[SOURCE: ISO 15930-7:2010, 3.25]
3.43
sampling efficiency
ratio of the measured limiting resolution and the Nyquist frequency
Note 1 to entry: Both values need to have the same unit.
[SOURCE: ISO 19262:2015, 3.220]
3.44
sampling rate
number of samples per unit of time, angle, revolutions or other mechanical, independent variable for
uniformly sampled data
[SOURCE: ISO 18431-1:2005, 3.13]
3.45
scanner
electronic device that converts a fixed image, such as a film or film transparency, into an electronic signal
[SOURCE: ISO 21550:2004, 3.19]
3.46
scene referred image state
image state image state associated with image data that represents estimates of the colour-space
coordinates of the elements of a scene
Note 1 to entry: When the phrase “scene-referred” is used as a qualifier to an object, it implies that the object is in a
scene referred image state. For example, scene-referred image data are image data in a scene-referred image state.
Note 2 to entry: Scene-referred image data can be determined from raw DSC image data before colour-rendering
is performed. Generally, DSCs do not write scene-referred image data in image files, but some do so in a special
mode intended for this purpose. Typically, DSCs write standard output-referred image data where colour-
rendering has already been performed.
Note 3 to entry: Scene-referred image data typically represents relative scene colourimetry estimates.
Absolute scene colourimetry estimates can be calculated using a scaling factor. The scaling factor can be
derived from additional information such as the image OECF, F-number or ApertureValue, and ExposureTime or
ShutterSpeedValue tags.
Note 4 to entry: Scene-referred image data can contain inaccuracies due to the dynamic range limitations of the
capture device, noise from various sources, quantization, optical blurring and flare that are not corrected for,
and colour analysis errors due to capture device metamerism. In some cases, these sources of inaccuracy can be
significant.
8 © ISO 2017 – All rights reserved

Note 5 to entry: The transformation from raw DSC image data to scene-referred image data depends on the relative
adopted whites selected for the scene and the colour space used to encode the image data. If the chosen scene
adopted white is inappropriate, additional errors will be introduced into the scene-referred image data. These
errors can be correctable if the transformation used to produce the scene-referred image data are known, and the
colour encoding used for the incorrect scene-referred image data has adequate precision and dynamic range.
Note 6 to entry: The scene can correspond to an actual view of the natural world, or be a computer-generated
virtual scene simulating such a view. It can also correspond to a modified scene determined by applying
modifications to an original scene to produce some different desired scene. Any such scene modifications need
to leave the image in a scene referred image state, and need to be done in the context of an expected colour-
rendering transform.
[SOURCE: ISO/TS 22028-3:2012, 3.18]
3.47
shading
variation of signal components within the image field
[SOURCE: ISO 19262:2015, 3.231]
3.48
sharpening
amplification of the SFR by means of image processing to achieve sharper appearing images
Note 1 to entry: Also, a class of image processing operations that enhances the contrast of selective spatial
frequencies, usually visually important ones.
[SOURCE: ISO 19262:2015, 3.232]
3.49
signal-to-noise ratio
SNR
ratio of the incremental output signal to the root mean square (rms) noise level, at a particular signal level
[SOURCE: ISO 19262:2015, 3.235]
3.50
slow scan direction
direction in which the scanner moves the photo elements (perpendicular to the lines of active photo
elements in a linear array image sensor)
[SOURCE: ISO 16067-1:2003, 3.16]
3.51
spatial frequency response
SFR
measured amplitude response of an imaging system as a function of relative input spatial frequency
Note 1 to entry: The SFR is normally represented by a curve of the output response to an input signal of unit
amplitude, over a range of spatial frequencies.
Note 2 to entry: The SFR is normalized to yield a value of unity at a spatial frequency of 0.
Note 3 to entry: In equations, the symbol RSFR rather than the abbreviation SFR is used for clarity.
[SOURCE: ISO 12231:2012, 3.168]
3.52
test chart
arrangement of test patterns designed to test particular aspects of an imaging system
[SOURCE: ISO 12233:2017, 3.26]
3.53
test pattern
specified arrangement of spectral reflectance or transmittance characteristics used in measuring an
imaging systems quality attribute
[SOURCE: ISO 12233:2017, 3.27]
3.54
tone
degree of lightness or darkness in any given area of an image
[SOURCE: ISO 12637-2:2008, 2.132]
3.55
vertical resolution
resolution value measured in the shorter image dimension, corresponding to the vertical direction for a
“landscape” image orientation, typically using a horizontally oriented test chart feature
[SOURCE: ISO 12233:2017, 3.28]
3.56
white balance
adjustment of electronic still picture colour channel gains or image processing so that radiation with
relative spectral power distribution equal to that of the scene illumination source is rendered as a
visual neutral
[SOURCE: ISO 14524:2009, 3.16]
4 System setup and calibration
4.1 General
The image capture system needs to be carefully set up to ensure consistent, repeatable, and high quality
results. Prior to checking or confirming the quality of the system, it always needs to be accurately
calibrated and adjusted. For a more detailed description on how to set up and calibrate an imaging
system prior to imaging systems quality analysis see ISO/TR 19263.
4.2 System configuration
The camera needs to be mounted on a solid stand that does not move during exposure. Any ambient
light that does not originate from the desired illumination shall be avoided.
4.3 Camera/scanner settings
The lowest sensitivity and lowest image compression rate, i.e. the highest image quality, should be
selected.
4.4 Exposure
The exposure shall be adjusted so a diffuse white flat surface (a test chart may be used for this) is
captured and recorded using encoding values that have an L* value equal to the actual L* value of the
diffuse white flat surface. In the case of a three-dimensional original the placement and orientation
of the diffuse white flat surface are left to the photographer, but should result in a reasonable image
appearance (when displayed accurately) compared to viewing the original. The user needs to make
sure that the dark areas are also not clipped. If clipping in the black areas is encountered, the user
needs to ensure that the system is able to capture the dynamic range of the original referring to the
measurement described in ISO 21550.
10 © ISO 2017 – All rights reserved

4.5 White balancing
The white balance shall be measured on a grey card or a white card (without optical brighteners)
to ensure correct and consistent results. This grey reference is required to be spectrally neutral in
reflection and the surrounding shall not have a dominating colour. These settings shall be stored and
used for production afterwards. This process shall be repeated on a regular basis to compensate for the
spectral change of the light source over its lifetime. Depending on the type of light source the interval in
which this needs to be done varies.
White balance performed on different tonal levels can vary. Highlights are generally more sensitive to
errors. To check the variances of a system, it is best to use a grey scale and try different tonal levels.
4.6 ICC Profiling
If the originals are captured using a colour imaging system, an ICC profile should be created to
characterize the system. For the purpose of ICC profiling, an ideal colour test chart reflects the type of
originals to be digitized in terms of matching material and colourants.
If the software does not support ICC colour management, it is critical to determine if the system sensor,
or any internal calibration, reaches accurate colour reproduction in the desired encoding before you
decide to purchase or use the system.
4.7 Focusing
The system shall correctly be focused on the original. It depends on the tools the system has available
how a good focus level can be achieved. Auto focus systems are often not reliable and may have problems
focusing on certain originals without the introduction of focus aids.
4.8 Colour encoding
The desired colour encoding should be selected based on the intended application requirements and
workflow preferences. In ISO 22028-1:2016, Annex B lists the characteristics and source standards for
a number of standard colour encodings and Annex C provides criteria for selection of colour encodings.
In general, original- and scene-referred encodings are most appropriate for digital archiving systems.
Examples of original-referred images are provided in ISO 12640-3, and examples of scene-referred
images are provided in ISO 12640-5. However, at the time of the drafting of this document, very few
scanners and digital cameras or raw processing applications supported either original- or scene-
referred encodings, making it necessary to adapt output-referred encodings to this use.
When adapting output-referred encodings for the purpose of digital archiving, several changes to normal
practice should be made in the processing, encoding, interpretation and display of the image data:
a) When processing the image data for encoding, any colour rendering should be turned off to the
extent possible, so that the image colourimetry encoded accurately represents the colourimetry
of the original object, with chromatic adaptation to the encoding white point. Particular attention
should be paid to processing controls that apply nonlinear tone reproduction, or black or white
clipping.
b) If it is not possible to turn off the colour rendering in the processing, profiling should be used to
undo it to the extent possible, and the result
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