ISO 20462-1:2005
(Main)Photography — Psychophysical experimental methods for estimating image quality — Part 1: Overview of psychophysical elements
Photography — Psychophysical experimental methods for estimating image quality — Part 1: Overview of psychophysical elements
ISO 20462-1:2005 is part of a three-part standard pertaining to the subjective evaluation of pictorial still image quality. ISO 20462-1:2005 defines the units by which image quality is quantified (just noticeable differences, or JNDs); describes the influence of stimulus properties, observer characteristics, and task instructions on results obtained from rating experiments; and provides a flow chart for choosing the preferred psychophysical method for determining image quality from among those defined in subsequent parts of ISO 20462.
Photographie — Méthodes psychophysiques expérimentales pour estimer la qualité d'image — Partie 1: Aperçu général des éléments psychophysiques
Fotografija - Psihofizične eksperimentalne metode za ocenjevanje slikovne kakovosti - 1. del: Pregled psihofizičnih dejavnikov
Ta del ISO 20462 je del večdelnega standarda, ki se nanaša na subjektivno vrednotenje slikovne kakovosti mirujočih slik. Ta del ISO 20462 a) opredeljuje enote, s katerimi se ovrednoti kakovost slike (komaj zaznavne razlike oz. JND); b) opisuje vpliv lastnosti dražljajev, značilnosti opazovalca in navodil za nalogo na rezultate, dobljene iz ocenjevalnih eksperimentov; c) podaja shematski prikaz za izbor prednostne psihofizične metode za določanje kakovosti slike izmed metod, navedenih v naslednjih delih ISO 20462.
General Information
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.VOLNRYQHPhotographie - Méthodes psychophysiques expérimentales pour estimer la qualité d'image - Partie 1: Aperçu général des éléments psychophysiquesPhotography - Psychophysical experimental methods for estimating image quality - Part 1: Overview of psychophysical elements37.040.01Fotografija na splošnoPhotography in generalICS:Ta slovenski standard je istoveten z:ISO 20462-1:2005SIST ISO 20462-1:2011en01-julij-2011SIST ISO 20462-1:2011SLOVENSKI
STANDARD
Reference numberISO 20462-1:2005(E)© ISO 2005
INTERNATIONAL STANDARD ISO20462-1First edition2005-11-01Photography — Psychophysical experimental methods for estimating image quality — Part 1: Overview of psychophysical elements Photographie — Méthodes psychophysiques expérimentales pour estimer la qualité d'image — Partie 1: Aperçu général des éléments psychophysiques
©
ISO 2005 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 • CH-1211 Geneva 20 Tel.
+ 41 22 749 01 11 Fax
+ 41 22 749 09 47 E-mail
copyright@iso.org Web
www.iso.org Published in Switzerland
ii
iiiContents Page Foreword.iv Introduction.v 1 Scope.1 2 Normative references.1 3 Terms and definitions.1 4 Specification of the experimental conditions and results.5 4.1 Observer characteristics.5 4.2 Stimulus properties.6 4.3 Instructions to the observer.6 4.4 Viewing conditions.7 4.5 Experimental duration.7 4.6 Results.8 4.7 Summary of reported quantities.8 Annex A (informative)
Selection of an appropriate psychophysical method.9 Annex B (informative)
Stimulus differences, paired comparison proportions, and JNDs.11 Annex C (informative)
Example of a report of a psychophysical experiment.13 Annex D (informative)
Comparison of selected psychometric methods.15 Bibliography.17
vIntroduction There are many circumstances under which it is desirable to quantify image quality in a standardized fashion that facilitates interpretation of results within a given experiment and/or comparison of results between different experiments. Such information can be of value in assessing the performance of different capture or display devices, image processing algorithms, etc. under various conditions. There are a number of psychometric methods described in the literature, such as paired comparison, rank ordering, categorical sort, and magnitude estimation, which might be considered as candidates for experimentally measuring image quality. Several textbooks[1] [3] [4] [5] [9] [12] have reviewed these and other methods and have discussed associated data reduction techniques, which usually are based upon the approach of Thurstone[11] or analogous reasoning. However, the choice of the best method for a particular application may be difficult to make, and interpretation of the rating scales produced by the numerical analyses is frequently ambiguous. Furthermore, none of the commonly used techniques provides an efficient mechanism for calibration of the results against a standardised numerical scale or associated physical references, which is desirable when results of different experiments are to be compared or integrated. The value of new calibrated psychometric methods in developing comprehensive models of imaging system quality has been demonstrated in a recent work[6] that contains more detailed discussions of many of the informative topics superficially considered herein. The three parts of ISO 20462 address the need for documented means of determining image quality in a calibrated fashion. Part 1 provides an overview of practical psychophysics; specific experimental methods and associated data reduction techniques are described in Part 2 (triplet comparison method[8] [10]) and Part 3 (quality ruler method[6]). Informative Annex A aids in identifying the better choice between the two alternative methods of Parts 2 to 3, which are complementary and together are sufficient to span a wide range of applications. It is the intent of these methods to produce results that are not merely directional in nature, but are expressed in terms of relative or fixed scales that are calibrated in just noticeable differences (JNDs), so that the significance of experimentally measured stimulus differences is readily ascertained. SIST ISO 20462-1:2011
INTERNATIONAL STANDARD ISO 20462-1:2005(E) © ISO 2005 – All rights reserved
1Photography — Psychophysical experimental methods for estimating image quality — Part 1: Overview of psychophysical elements 1 Scope This part of ISO 20462 is part of a multiple-part standard pertaining to the subjective evaluation of pictorial still image quality. This part of ISO 20462 a) defines the units by which image quality is quantified (just noticeable differences, or JNDs); b) describes the influence of stimulus properties, observer characteristics, and task instructions on results obtained from rating experiments; c) provides a flow chart for choosing the preferred psychophysical method for determining image quality from among those defined in subsequent parts of ISO 20462. 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 3664, Viewing conditions — Graphic technology and photography 3 Terms and definitions For the purpose of this document, the following terms and definitions apply: 3.1 artefactual attribute attribute of image quality that, when evident in an image, nearly always leads to a loss of overall image quality EXAMPLE Examples of artefactual attributes include noise and aliasing. NOTE The commonly used terms defect and impairment are similar in meaning. 3.2 attribute aspect, dimension, or component of overall image quality cf. artefactual attribute (3.1) and preferential attribute (3.12) SIST ISO 20462-1:2011
JND stimulus difference that leads to a 75:25 proportion of responses in a paired comparison task cf. attribute JND (3.3) and qua
...
INTERNATIONAL ISO
STANDARD 20462-1
First edition
2005-11-01
Photography — Psychophysical
experimental methods for estimating
image quality —
Part 1:
Overview of psychophysical elements
Photographie — Méthodes psychophysiques expérimentales pour
estimer la qualité d'image —
Partie 1: Aperçu général des éléments psychophysiques
Reference number
©
ISO 2005
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© ISO 2005
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2005 – All rights reserved
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 Specification of the experimental conditions and results. 5
4.1 Observer characteristics. 5
4.2 Stimulus properties . 6
4.3 Instructions to the observer . 6
4.4 Viewing conditions . 7
4.5 Experimental duration. 7
4.6 Results. 8
4.7 Summary of reported quantities . 8
Annex A (informative) Selection of an appropriate psychophysical method . 9
Annex B (informative) Stimulus differences, paired comparison proportions, and JNDs . 11
Annex C (informative) Example of a report of a psychophysical experiment. 13
Annex D (informative) Comparison of selected psychometric methods. 15
Bibliography . 17
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 20462-1 was prepared by Technical Committee ISO/TC 42, Photography.
ISO 20462 consists of the following parts, under the general title Photography — Psychophysical experimental
methods for estimating image quality:
⎯ Part 1: Overview of psychophysical elements
⎯ Part 2: Triplet comparison method
⎯ Part 3: Quality ruler method
iv © ISO 2005 – All rights reserved
Introduction
There are many circumstances under which it is desirable to quantify image quality in a standardized fashion
that facilitates interpretation of results within a given experiment and/or comparison of results between
different experiments. Such information can be of value in assessing the performance of different capture or
display devices, image processing algorithms, etc. under various conditions. There are a number of
psychometric methods described in the literature, such as paired comparison, rank ordering, categorical sort,
and magnitude estimation, which might be considered as candidates for experimentally measuring image
[1] [3] [4] [5] [9] [12]
quality. Several textbooks have reviewed these and other methods and have discussed
[11]
associated data reduction techniques, which usually are based upon the approach of Thurstone or
analogous reasoning. However, the choice of the best method for a particular application may be difficult to
make, and interpretation of the rating scales produced by the numerical analyses is frequently ambiguous.
Furthermore, none of the commonly used techniques provides an efficient mechanism for calibration of the
results against a standardised numerical scale or associated physical references, which is desirable when
results of different experiments are to be compared or integrated. The value of new calibrated psychometric
methods in developing comprehensive models of imaging system quality has been demonstrated in a recent
[6]
work that contains more detailed discussions of many of the informative topics superficially considered
herein.
The three parts of ISO 20462 address the need for documented means of determining image quality in a
calibrated fashion. Part 1 provides an overview of practical psychophysics; specific experimental methods and
[8] [10]
associated data reduction techniques are described in Part 2 (triplet comparison method ) and Part 3
[6]
(quality ruler method ). Informative Annex A aids in identifying the better choice between the two alternative
methods of Parts 2 to 3, which are complementary and together are sufficient to span a wide range of
applications. It is the intent of these methods to produce results that are not merely directional in nature, but
are expressed in terms of relative or fixed scales that are calibrated in just noticeable differences (JNDs), so
that the significance of experimentally measured stimulus differences is readily ascertained.
INTERNATIONAL STANDARD ISO 20462-1:2005(E)
Photography — Psychophysical experimental methods
for estimating image quality —
Part 1:
Overview of psychophysical elements
1 Scope
This part of ISO 20462 is part of a multiple-part standard pertaining to the subjective evaluation of pictorial still
image quality. This part of ISO 20462
a) defines the units by which image quality is quantified (just noticeable differences, or JNDs);
b) describes the influence of stimulus properties, observer characteristics, and task instructions on results
obtained from rating experiments;
c) provides a flow chart for choosing the preferred psychophysical method for determining image quality
from among those defined in subsequent parts of ISO 20462.
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 3664, Viewing conditions — Graphic technology and photography
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply:
3.1
artefactual attribute
attribute of image quality that, when evident in an image, nearly always leads to a loss of overall image quality
EXAMPLE Examples of artefactual attributes include noise and aliasing.
NOTE The commonly used terms defect and impairment are similar in meaning.
3.2
attribute
aspect, dimension, or component of overall image quality
cf. artefactual attribute (3.1) and preferential attribute (3.12)
EXAMPLE Examples of image quality attributes include image structure properties such as sharpness and noise;
colour and tone reproduction properties such as contrast, colour balance, and relative colourfulness; and digital artefacts
such as aliasing, contouring, and compression defects.
3.3
attribute just noticeable difference
attribute JND
measure of the detectability of appearance variations, corresponding to a stimulus difference that leads to a
75:25 proportion of responses in a paired comparison task in which univariate stimuli pairs are assessed in
terms of a single attribute identified in the instructions
cf. quality JND (3.14)
NOTE 1 As an example, a paired comparison identifying the sharper of two stimuli that differ only in their generating
system modulation transfer function (MTF), would yield results in terms of sharpness attribute JNDs. If the MTF curves
differed monotonically and did not cross, the outcome of the paired comparison would depend primarily upon the
observers’ ability to detect changes in the appearance of the stimuli as a function of MTF variations, with little or no value
judgement required of the observers. The relationship between paired comparison proportions and stimulus differences is
discussed in greater detail in Annex B.
NOTE 2 If observers are instead asked to choose which of a pair of stimuli is higher in overall image quality, and if the
stimuli in aggregate are multivariate, such that the observer should make value judgements of the importance of a number
of attributes, rather than focussing on one aspect of image appearance, it is observed experimentally that larger objective
stimulus differences (for example, MTF changes) are required to obtain a 75:25 proportion of responses, which in this
case corresponds to a quality JND.
NOTE 3 A JND is a statistical quantity, derived from a number of observations. An observer assessing a single pair of
images differing by one attribute JND is unlikely to be confident that he or she has detected the sample difference. A
stimulus difference of approximately three JNDs is usually needed for an observer of average sensitivity to feel reasonably
certain of his or her assessment.
3.4
categorical sort method
psychophysical method involving the classification of a stimulus into one of several ordered categories, at
least some of which are identified by adjectives or phrases that describe different levels of image quality or
attributes thereof
NOTE The application of adjectival descriptors is strongly affected by the range of stimuli presented, so that it is
difficult to compare the results of one categorical sort experiment to another. Range effects and the coarse quantization of
categorical sort experiments also hinder conversion of the responses to JND units. Given these limitations, it is not
possible to unambiguously map adjectival descriptors to JND units, but it is worth noting that in some experiments where a
broad range of stimuli have been presented, the categories excellent, very good, good, fair, poor, and not worth keeping
have been found to provide very roughly comparable intervals that average about six quality JNDs in width.
3.5
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 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.
3.6
instructions
set of directions given to the observer for performing the psychophysical evaluation task
3.7
just noticeable difference
JND
stimulus difference that leads to a 75:25 proportion of responses in a paired comparison task
cf. attribute JND (3.3) and quality JND (3.14)
2 © ISO 2005 – All rights reserved
3.8
magnitude estimation method
psychophysical method involving the
...
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