1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 20462-3:2012Photography Psychophysicalexperimental methods forestimating image qualityPart 3: Quality ruler methodBS ISO 20462-3:2012 BRITISH STANDARDNational forewordThis
2、 British Standard is the UK implementation of ISO 20462-3:2012.It supersedes BS ISO 20462-3:2005 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee CPW/42, Photography.A list of organizations represented on this committee can beobtained on request to its s
3、ecretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2012. Published by BSI StandardsLimited 2012ISBN 978 0 580 69819 4ICS 37.040.01Compliance with a British Standard canno
4、t confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 30 June 2012.Amendments issued since publicationDate T e x t a f f e c t e dBS ISO 20462-3:2012 ISO 2012Photography Psychophysical experimental methods for
5、 estimating image quality Part 3: Quality ruler methodPhotographie Mthodes psychophysiques exprimentales pour estimer la qualit dimage Partie 3: Mthode de la rgle de qualitINTERNATIONAL STANDARDISO20462-3Second edition2012-05-15Reference numberISO 20462-3:2012(E)BS ISO 20462-3:2012ISO 20462-3:2012(E
6、)ii ISO 2012 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2012All 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 f
7、rom either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 20462-3:2012ISO 20462-3:2012(E) ISO 2012 All ri
8、ghts reserved iiiContents PageForeword ivIntroduction v1 Scope 12 Normative references . 13 Terms and definitions . 14 Quality ruler experiments 54.1 General properties of quality rulers . 54.2 Experimental conditions and reported results 54.3 Attributes varied in quality rulers . 55 Hardcopy qualit
9、y ruler implementation . 65.1 Physical apparatus . 65.2 Reference stimuli . 76 Softcopy quality ruler implementation 86.1 Physical apparatus . 86.2 Reference stimuli . 86.3 Controlling software . 87 Generation of quality ruler stimuli 97.1 General requirements . 97.2 Modulation transfer functions (M
10、TFs) .107.3 Scene-dependent ruler calibration . 118 Standard quality scale (SQS) determinations .128.1 Properties of the SQS .128.2 Experimental requirements for measuring primary SQS1.128.3 Experimental requirements for measuring secondary SQS212Annex A (informative) Sample instructions for a hardc
11、opy quality ruler experiment 13Annex B (informative) Sample instructions for softcopy ruler experiments using binary sort paired comparison 15Annex C (informative) Sample code of a binary search routine for the softcopy quality ruler .17Annex D (informative) Calibration of the standard quality scale
12、 (SQS) and its reference stimuli 19Annex E (informative) Example of results from quality ruler experiments .21Annex F (informative) Sample instructions for a softcopy ruler experiment using slider bar matching 25Bibliography .26BS ISO 20462-3:2012ISO 20462-3:2012(E)ForewordISO (the International Org
13、anization 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 establi
14、shed 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 standardizatio
15、n.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. Pu
16、blication 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
17、 rights.ISO 20462-3 was prepared by Technical Committee ISO/TC 42, Photography.This second edition cancels and replaces the first edition (ISO 20462-3:2005), which has been technically revised.ISO 20462 consists of the following parts, under the general title Photography Psychophysical experimental
18、methods for estimating image quality: Part 1: Overview of psychophysical elements Part 2: Triplet comparison method Part 3: Quality ruler methodiv ISO 2012 All rights reservedBS ISO 20462-3:2012ISO 20462-3:2012(E)IntroductionThere are many circumstances under which it is desirable to quantify image
19、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.
20、under various conditions. However, the choice of the best psychometric 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 rating techniques provides a
21、n efficient mechanism for calibration of the results against a standardized numerical scale or associated physical references, which is desirable when results of different experiments are to be compared or integrated.ISO 20462-1, ISO 20462-2 and this part of ISO 20462 address the need for documented
22、 means of determining image quality in a calibrated fashion. ISO 20462-1 provides an overview of practical psychophysics and aids in identifying the better choice between the two alternative approaches described in ISO 20462-2 (triplet comparison method234) and this part of ISO 20462 (quality ruler
23、method5). These two techniques are complementary and together are sufficient to span a wide range of practical applications. ISO 20462-2 and this part of ISO 20462 document both specific experimental methods and associated data reduction techniques. It is the intent of these methods to produce resul
24、ts that are not merely directional in nature, but are expressed in terms of relative or fixed scales that are calibrated in terms of just noticeable differences (JNDs), so that the significance of experimentally measured stimulus differences is readily ascertained.The quality ruler method described
25、in this part of ISO 20462 is particularly suitable for measuring quality differences exceeding one JND. The ratings given by an observer can be converted to JND values in real time, rather than having to wait until the entire experimental data set has been collected and analysed. Furthermore, with s
26、uitable reference stimuli, the quality ruler method permits the results to be reported using the standard quality scale (SQS), a fixed numerical scale that:a) is anchored against physical standards;b) has one unit corresponding to one JND; andc) has a zero point corresponding to an image having litt
27、le identifiable information content.Reflection prints calibrated against the absolute SQS, which are referred to as standard reference stimuli (SRS), will be available at the Standards Resources link at www.imaging.org. Digital Reference Stimuli (DRS) will also be provided at the Standards Resources
28、 link at www.imaging.org. These images, when displayed on a high-quality monitor and viewed correctly, will have approximately known absolute SQS values, and accurately known relative SQS values (JNDs). Included with the images will be software for running softcopy quality ruler experiments. This pa
29、rt of ISO 20462 also describes how users can conveniently generate their own quality ruler images with correct relative calibrations and, if desired, calibrate them absolutely against the SRS.The International Organization for Standardization (ISO) draws attention to the fact that it is claimed that
30、 compliance with this document may involve the use of US Patent Numbers 6,639,999 and 6,658,139 concerning the quality ruler given in Clauses 4 to 6.ISO takes no position concerning the evidence, validity and scope of this patent right.The holder of this patent right has ensured ISO that he is willi
31、ng to negotiate licences under reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this respect, the statement of the holder of this patent right is registered with ISO. Patent inquiries may be addressed to:General Council and Senior Vice PresidentEastman
32、Kodak Company345 State StreetRochester, NY 14650USA ISO 2012 All rights reserved vBS ISO 20462-3:2012ISO 20462-3:2012(E)Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights other than those identified above. ISO shall not be held respon
33、sible for identifying any or all such patent rights.vi ISO 2012 All rights reservedBS ISO 20462-3:2012INTERNATIONAL STANDARD ISO 20462-3:2012(E)Photography Psychophysical experimental methods for estimating image quality Part 3: Quality ruler method1 ScopeThis part of ISO 20462 specifies:a) the natu
34、re of a quality ruler;b) hardcopy and softcopy implementations of quality rulers;c) how quality rulers may be generated or obtained; andd) the standard quality scale (SQS), a fixed numerical scale that may be measured using quality rulers.2 Normative referencesThe following referenced documents are
35、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, Graphic technology and photography Viewing conditions3 Terms and definitionsFor
36、 the purposes of this document, the following terms and definitions apply.3.1artefactual attributeattribute of image quality that, when evident in an image, nearly always leads to a loss of overall image qualityEXAMPLES Noise, aliasing.NOTE The commonly used terms “defect” and “impairment” are simil
37、ar in meaning.3.2attributeaspect, dimension, or component of overall image qualitycf. artefactual attribute (3.1) and preferential attribute (3.11)EXAMPLES Image structure properties such as sharpness and noise; colour and tone reproduction properties such as contrast, colour balance, and relative c
38、olourfulness; digital artefacts such as aliasing, contouring, and compression defects.3.3digital reference stimuliDRSset of digital images used in the softcopy ruler, which vary in sharpness and are calibrated against the standard quality scale (SQS) when suitably displayed and viewedNOTE The DRS wi
39、ll be available at the Standards Resources link at www.imaging.org. ISO 2012 All rights reserved 1BS ISO 20462-3:2012ISO 20462-3:2012(E)3.4image qualityimpression of the overall merit or excellence of an image, as perceived by an observer neither associated with the act of photography nor closely in
40、volved with the subject matter depictedNOTE 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 desig
41、ners.3.5instructionsset of directions given to the observer for performing the psychophysical evaluation task3.6just noticeable differenceJNDstimulus difference that leads to a 75:25 proportion of responses in a paired comparison taskcf. quality JND (3.13)3.7magnitude estimation methodpsychophysical
42、 method involving the assignment of a numerical value to each test stimulus that is proportional to image quality; typically, a reference stimulus with an assigned numerical value is present to anchor the rating scaleNOTE The numerical scale resulting from a magnitude estimation experiment is usuall
43、y assumed to constitute a ratio scale which, ideally, is a scale in which a constant percentage change in value corresponds with one JND. In practice, modest deviations from this behaviour occur, complicating the transformation of the rating scale into units of JNDs without inclusion of unidentified
44、 reference stimuli (having known quality) among the test stimuli.3.8multivariateseries of test or reference stimuli varying in multiple attributes of image quality3.9observerindividual performing the subjective evaluation task in a psychophysical method3.10paired comparison methodpsychophysical meth
45、od involving the choice of which of two simultaneously presented stimuli exhibits greater or lesser image quality or an attribute thereof, in accordance with a set of instructions given to the observerNOTE 1 Two limitations of the paired comparison method are as follows.a) If all possible stimulus c
46、omparisons are done, as is usually the case, a large number of assessments are required for even modest numbers of experimental stimulus levels if n levels are to be studied, n (n 1)/2 paired comparisons are needed.b) If a stimulus difference exceeds approximately 1,5 JNDs, the magnitude of the stim
47、ulus difference cannot be directly estimated reliably because the response saturates as the proportions approach unanimity.NOTE 2 However, if a series of stimuli having no large gaps are assessed, the differences between more widely separated stimuli may be deduced indirectly by summing smaller, rel
48、iably determined (unsaturated) stimulus differences. The standard methods for transformation of paired comparison data to an interval scale (a scale linearly related to JNDs) perform statistically optimized procedures for inferring the stimulus differences, but they may yield unreliable results when
49、 saturated responses are included in the analysis.3.11preferential attributeattribute of image quality that is invariably evident in an image, and for which the preferred degree is a matter of opinion, depending upon both the observer and the image contentEXAMPLES Colour and tone reproduction properties such as contrast and relative colourfulness.2 ISO 2012 All rights reservedBS ISO 20462-3:2012ISO 20462-3:2012(E)NOTE 1 Because the perceived quality associated with a preferential attribute is dependent upon both the observ
