ISO 19264-1:2021
(Main)Photography — Archiving systems — Imaging systems quality analysis — Part 1: Reflective originals
Photography — Archiving systems — Imaging systems quality analysis — Part 1: Reflective originals
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.
Photographie — Systèmes d'archivage — Analyse de la qualité des systèmes d'image — Partie 1: Documents réfléchissants
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INTERNATIONAL ISO
STANDARD 19264-1
First edition
2021-06
Photography — Archiving systems —
Imaging systems quality analysis —
Part 1:
Reflective originals
Photographie — Systèmes d'archivage — Analyse de la qualité des
systèmes d'image —
Partie 1: Documents réfléchissants
Reference number
ISO 19264-1:2021(E)
©
ISO 2021
---------------------- Page: 1 ----------------------
ISO 19264-1:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 19264-1:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 System setup and calibration . 6
4.1 General . 6
4.2 System configuration . 6
4.3 Camera/scanner settings . 6
4.4 Exposure . 6
4.5 White balancing . 6
4.6 ICC Profiling . 7
4.7 Focusing . 7
4.8 Colour encoding . 7
4.9 Reproduction scale . 8
5 Imaging system quality analysis procedure . 8
6 Imaging systems quality characteristics and metrics . 8
6.1 General . 8
6.2 Tones and noise . 9
6.3 Colour .11
6.4 Details .13
6.5 Geometry .14
7 Reporting results .15
7.1 General .15
7.2 Example report for tone reproduction results .16
7.3 Gain modulation .17
7.4 Dynamic range.19
7.5 Noise .19
7.6 Banding .20
7.7 Defect pixels .22
7.8 White balance.22
7.9 Colour reproduction .23
7.10 Colour mis-registration .24
7.11 Sampling rate.24
7.12 Resolution .24
7.13 MTF 50/MTF 10 .24
7.14 Sharpening .24
7.15 Acutance .24
7.16 Lightness non-uniformity .24
7.17 Chrominance non-uniformity .24
7.18 Distortion .24
7.19 Reproduction scale .24
Annex A (normative) Test chart requirements .25
Annex B (informative) Guidelines for imaging performance aims and tolerances .27
Annex C (informative) Example of multi-pattern chart: Universal Test Target (UTT) .29
Bibliography .49
© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 19264-1:2021(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
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 (see 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 (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 of the voluntary nature of standards, 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 www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 42, Photography.
This first edition of ISO 19264-1 cancels and replaces the first edition of ISO/TS 19264-1, which has
been technically revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 19264-1:2021(E)
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 [29] and [32] 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
[42]
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.
© ISO 2021 – All rights reserved v
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INTERNATIONAL STANDARD ISO 19264-1:2021(E)
Photography — Archiving systems — Imaging systems
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
ISO/CIE 11664-4, Colorimetry — Part 4: CIE 1976 L*a*b* colour space
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 https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
© ISO 2021 – All rights reserved 1
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ISO 19264-1:2021(E)
3.1
acutance
numerical value that correlates to some extent with subjective image sharpness
[SOURCE: ISO 19262:2015, 3.1]
3.2
banding
unwanted stripes or bands that occur in a digital image
Note 1 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.]
3.3
checkerboard
regular squared dark and bright structure on a surface like the one used on a chess board
[SOURCE: ISO 19262:2015, 3.18]
3.4
colour misregistration
colour-to-colour spatial dislocation of otherwise spatially coincident colour features of an imaged object
[SOURCE: ISO 19262:2015, 3.42]
3.5
digitization
act of generating a digital (quantized) representation of a continuous signal
[SOURCE: ISO 20998-1:2006, 2.7, modified — The Note 1 to entry has been deleted.]
3.6
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 asymmetry of a camera lens or position shift processing in a camera imaging process.
[SOURCE: ISO 19262:2015, 3.82]
3.7
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]
2 © ISO 2021 – All rights reserved
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ISO 19264-1:2021(E)
3.7.1
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]
3.8
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.]
3.9
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]
3.10
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]
3.11
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.
3.12
limiting resolution
value of that portion of a specified resolution (3.21) 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
3.13
modulation
difference between the minimum and maximum signal levels divided by the sum of these levels
[SOURCE: ISO/IEC 29112:2012, 3.17]
3.14
noise
unwanted variations in the response of an imaging system
[SOURCE: ISO 15739:2013, 3.9]
© ISO 2021 – All rights reserved 3
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ISO 19264-1:2021(E)
3.15
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]
3.16
original-referred
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.]
3.17
output-referred
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.
4 © ISO 2021 – All rights reserved
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ISO 19264-1:2021(E)
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]
3.18
profiling
creation of (ICC) colour profiles for imaging devices in order to enhance the accuracy in colour
reproduction
[SOURCE: ISO 19262:2015, 3.197]
3.19
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]
3.20
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]
3.21
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, spatial 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.]
3.22
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]
3.23
scene referred
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 referre
...
INTERNATIONAL ISO
STANDARD 19264-1
First edition
Photography — Archiving systems —
Imaging systems quality analysis —
Part 1:
Reflective originals
Photographie — Systèmes d'archivage — Analyse de la qualité des
systèmes d'image —
Partie 1: Documents réfléchissants
Member bodies are requested to consult relevant national interests in ISO/TC
46/SC 11,ISO/TC 171 before casting their ballot to the e-Balloting application.
PROOF/ÉPREUVE
Reference number
ISO 19264-1:2021(E)
©
ISO 2021
---------------------- Page: 1 ----------------------
ISO 19264-1:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 19264-1:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 System setup and calibration . 6
4.1 General . 6
4.2 System configuration . 6
4.3 Camera/scanner settings . 6
4.4 Exposure . 6
4.5 White balancing . 6
4.6 ICC Profiling . 7
4.7 Focusing . 7
4.8 Colour encoding . 7
4.9 Reproduction scale . 8
5 Imaging system quality analysis procedure . 8
6 Imaging systems quality characteristics and metrics . 8
6.1 General . 8
6.2 Tones and noise . 9
6.3 Colour .11
6.4 Details .13
6.5 Geometry .14
7 Reporting results .16
7.1 General .16
7.2 Example report for tone reproduction results .16
7.3 Gain modulation .17
7.4 Dynamic range.19
7.5 Noise .19
7.6 Banding .20
7.7 Defect pixels .22
7.8 White balance.22
7.9 Colour reproduction .23
7.10 Colour mis-registration .24
7.11 Sampling rate.24
7.12 Resolution .24
7.13 MTF 50/MTF 10 .24
7.14 Sharpening .24
7.15 Acutance .24
7.16 Lightness non-uniformity .24
7.17 Chrominance non-uniformity .24
7.18 Distortion .24
7.19 Reproduction scale .24
Annex A (normative) Test chart requirements .25
Annex B (informative) Guidelines for imaging performance aims and tolerances .27
Annex C (informative) Example of multi-pattern chart: Universal Test Target (UTT) .29
Bibliography .49
© ISO 2021 – All rights reserved PROOF/ÉPREUVE iii
---------------------- Page: 3 ----------------------
ISO 19264-1:2021(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
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 (see 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 (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 of the voluntary nature of standards, 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 www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 42, Photography.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 19264-1:2021(E)
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 [29] and [32] 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
[42]
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.
© ISO 2021 – All rights reserved PROOF/ÉPREUVE v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 19264-1:2021(E)
Photography — Archiving systems — Imaging systems
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
ISO/CIE 11664-4, Colorimetry — Part 4: CIE 1976 L*a*b* colour space
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 https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
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ISO 19264-1:2021(E)
3.1
acutance
numerical value that correlates to some extent with subjective image sharpness
[SOURCE: ISO 19262:2015, 3.1]
3.2
banding
unwanted stripes or bands that occur in a digital image
Note 1 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.]
3.3
checkerboard
regular squared dark and bright structure on a surface like the one used on a chess board
[SOURCE: ISO 19262:2015, 3.18]
3.4
colour misregistration
colour-to-colour spatial dislocation of otherwise spatially coincident colour features of an imaged object
[SOURCE: ISO 19262:2015, 3.42]
3.5
digitization
act of generating a digital (quantized) representation of a continuous signal
[SOURCE: ISO 20998-1:2006, 2.7, modified — The Note 1 to entry has been deleted.]
3.6
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 asymmetry of a camera lens or position shift processing in a camera imaging process.
[SOURCE: ISO 19262:2015, 3.82]
3.7
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]
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ISO 19264-1:2021(E)
3.7.1
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]
3.8
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.]
3.9
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]
3.10
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]
3.11
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.
3.12
limiting resolution
value of that portion of a specified resolution (3.21) 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
3.13
modulation
difference between the minimum and maximum signal levels divided by the sum of these levels
[SOURCE: ISO/IEC 29112:2012, 3.17]
3.14
noise
unwanted variations in the response of an imaging system
[SOURCE: ISO 15739:2013, 3.9]
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ISO 19264-1:2021(E)
3.15
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]
3.16
original-referred
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.]
3.17
output-referred
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.
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ISO 19264-1:2021(E)
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]
3.18
profiling
creation of (ICC) colour profiles for imaging devices in order to enhance the accuracy in colour
reproduction
[SOURCE: ISO 19262:2015, 3.197]
3.19
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]
3.20
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]
3.21
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, spatial 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.]
3.22
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]
3.23
scene referred
image state image state associated with image data that represents estimates of the colour-space
coordinates of the elements of a scene
...
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