1、STD-ITU-T RECMN J.140-ENGL 1998 4862591 0649625 T20 INTERNATIONAL TELECOMMUNICATION UN ION ITU-T TELECOMMUN CATION STANDARDIZATION SECTOR OF ITU JA40 (03/98) SERIES J: TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Measurement of the quality of service Subjective picture qu
2、ality assessment for digital cable television systems ITU-T Recommendation J.140 (Previously CCITT Recommendation) JTU-T J-SERIES RECOMMENDATIONS TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS General Recommendations General specifications for analogue sound-programme trans
3、mission U J. 1-J.9 J. 10-J. 19 Performance characteristics of analogue sound-programme circuits Equipment and lines used for analogue sound-programme circuits Digital encoders for analogue sound-programme signals Digital transmission of sound-programme signals J.20-J.29 J.30-J.39 J.40-5.49 J.50-J.59
4、 3.60-5.69 J.70-J.79 Circuits for analogue television transmission links Analogue television transmission over metallic lines and interconnection with radio-relay Digital transmission of television signals Ancillary digital services for television transmission Operational requirements and methods fo
5、r television transmission Interactive systems for digital television distribution Transport of MPEG-2 signals on packetised networks J.80-J.89 J.90-J.99 J.100-J.109 J. 1 10-J. 129 J.130-J. 139 5.140-5.149 Digital television distribution through local subscriber networks J.150-J.159 Forfirther detail
6、s, please refer to ITU-T List of Recommendations. ITU-T RECOMMENDATION 5.140 SUBJECTIVE PICTURE QUALITY ASSESSMENT FOR DIGITAL CABLE TELEVISION SYSTEMS Summary This Recommendation specifies a subjective picture quality assessment method for digital cable television applications. Source ITU-T Recomme
7、ndation 5.140 was prepared by IT-T Study Group 9 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 18th of March 1998. Recommendation 5.140 (03/98) 1 - STD.ITU-T RECMN J.340-ENGL 3998 m 4662593 Ob49628 73T FOREWORD IT (International Telecommunication Union) is the United
8、Nations Specialized Agency in the field of telecommuni- cations. The IT Telecommunication Standardization Sector (ITU-T) is a permanent organ of the IT. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing te
9、lecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members
10、of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration” is used
11、for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The
12、IT takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had not received notice of intellec
13、tual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O IT 1998 All rights reserved. No part of this publ
14、ication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. 11 Recommendation 5.140 (03198) STD-ITU-T RECMN J.140-ENGL 1998 = 4862591 0649629 676 CONTENTS 1 Scope 2 References 3 Terms a
15、nd definitions . 4 Abbreviations . 5 General . 6 Test material . Annex A - Assessment method Single Stimulus Continuous Quality Evaluation (SSCQE) method A.2 Viewing parameters A . 1 Recommendation 5.140 (03/98) Page 1 1 1 2 2 . 111 STD-ITU-T RECMN J-340-ENGL 3998 4862593 0649630 398 Recommendation
16、5.140 SUBJECTIVE PICTURE QUALITY ASSESSMENT FOR DIGITAL CABLE TELEVISION SYSTEMS (Geneva, 1998) 1 Scope This Recommendation describes a subjective method for assessment of picture quality for digital cable television systems. It concerns all of the television chain from the signal source to users re
17、ceiver. This chain may contain satellite links, terrestrial links and/or cable links. The assessment is made using consumer grade receivers assuming a home viewing environment. 2 References The following ITU-T Recommendations, and other references contain provisions which, through reference in this
18、text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent ed
19、ition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. ITU-R Recommendation BT. 1 129-1 (1 995), Subjective assessment of standard definition digital television (SDTV) systems. ITU-R Recommendation BT.500-7 (1995),
20、Methodology for the subjective assessment of the qualis. of television pictures. ITU-R Recommendation BT. 121 0- 1 (1 997), Test materials to be used in subjective assessment. ITU-T Recommendation 5.84 (1999, Distribution of digital multi-programme signals for television, sound and data services thr
21、ough SMATV networks. ITU-T Recommendation 5.83 (1 995), Digital multi-programme systems for television, sound and data services for cable distribution. ITU-T Recommendation P.91 O (1 996), Subjective video qualis. assessment methods for multimedia applications. ITU-T Recommendation P.920 (1996), Int
22、eractive test methods for audiovisual communications. ITU-T Recommendation P.80 (1993), Methods for subjective determination of transmission quality. ITU-R Recommendation BT.8 14- 1 (1993), Specifications und alignment procedures for setting of brightness and contrast of displays. ITU-R Recommendati
23、on BT.8 15-1 (1 993), Specification of u signal for measurement of contrast ratio und displays. Terms and definitions This Recommendation defines the following term: 3.1 setting of brightness and contrast of the display. For details, see Recommendation ITU-R BT.814-1. PLUGE: Test signal consists of
24、a peak white level patch and several dark level patches/stripes used for the Recommendation 5.140 (03/98) 1 4 Abbreviations Capacity, critical applications (e.g. contribution) Performance of “adaptive“ systems This Recommendation uses the following abbreviations: Range, including very critical mater
25、ial for the application tested Material very critical for “adaptive“ scheme used PS Programme Segment PVD Preferred Viewing Distance QP Quality Parameter SDTV Standard Definition Television SSCQE Single Stimulus Continuous Quality Evaluation TP Test Presentation TS Test Session Identi weaknesses and
26、 possible improvements Identi factors on which systems are seen to vary 5 General Critical, aitribute-specific material Wide range of very rich material Subjective assessment methods are used to establish the performance of television systems using measurements that more directly anticipate the reac
27、tions of those who might view the systems tested. In this regard, it is understood that it may not be possible to fully characterize system performance by objective means; consequently, it is necessary to supplement objective measurements with subjective measurements. Conversion among different stan
28、dards In subjective method, test pictures, after passing through the measured line, are assessed by a group of assessors in specific viewing conditions and results of these tests are treated statistically. Critical for differences (e.g. field rate) In IT-R Recommendation BT.500-7, two classes of sub
29、jective assessment are given, and a few methods are representative of each class. Introduction of digital coding produces impairments to picture quality which are scene-dependent and time-varying. Methods of laboratory testing do not replicate home viewing condition of cable television. For the eval
30、uation of these types of picture quality, new methods are developed and tested. One of them is given in Annex A. Other methods are still under study and need validation. 6 Test material A number of approaches may be taken in establishing the kinds of test material required in television assessments.
31、 In practice, however, particular kinds of test materials should be used to address particular assessment problems. A survey of typical assessment problems and of test materials used to address these problems is given in Table 1. Table 1/5.140 - Selection of test material Assessment problem Material
32、 used I Overall performance with average material 1 General, “critical but not undulyo“ 1 2 Recommendation 5.140 (03198) - Some parameters may give rise to a similar order of impairments for most pictures or sequences. In such cases, results obtained with a very small number of pictures or sequences
33、 (e.g. two) may still provide a meaningful evaluation. However, digital systems frequently have an impact which depends heavily on the scene or sequence content. In such cases, there will be, for the totality of programme hours, a statistical distribution of impairment probability and picture or seq
34、uence content. Without knowing the form of distribution, which is usually the case, the selection of test material and interpretation of results must be done very carefully. In general, it is essential to include critical sequences, because it is possible to take this into account when interpreting
35、results, but it is not possible to extrapolate from non-critical material. In cases where scene or sequence content affects results, the material should be chosen to be “critical but not unduly so“ for the system under test. The phrase “not unduly so“ implies that the pictures could still conceivabl
36、y form part of normal programme hours. At least four items should, in such cases, be used: for example, half of which are definitely critical, and half of which are moderately critical. It is recommended that at least six picture sequences be used in the assessment, plus an additional one to be used
37、 for training purposes prior to the start of the trial. The sequences should range between moderately critical and definitely critical in the context of the bit-rate reduction application being considered. In subjective assessment, still pictures and moving sequences may be selected from those liste
38、d in ITU-R Recommendation BT.1210-1, Annex 1. In this respect, it should be noted that digitally-stored pictures and sequences, being the most reproducible source signals, are the preferred sources for assessment. Annex A Assessment method The methodologies applied are based on the SSCQE method deve
39、loped by the ITU-R and given in ITU-RRecommendation BT.500-7, and therefore it is desirable to refer to the latest actual method when ITU-R Recommendation BT.500-7 is modified. A.1 Single Stimulus Continuous Quality Evaluation (SSCQE) method In this method, observers are asked to assess instantaneou
40、s picture quality continuously during a test session with subjects viewing the material once without a source reference. A.1 .I Continuous assessment of overall quality A.l.l.l Recording device and set-up An electronic recording handset connected to a computer should be used for recording the contin
41、uous quality assessment from the subjects. This device should have the following characteristics: - slider mechanism without any sprung position; linear range of travel of 10 cm; - - fixed or desk-mounted position; - samples recorded twice a second. Recommendation 5.140 (03/98) 3 - - - - A.1.1.2 Sub
42、jects should be presented with test sessions of the following format: - General form of the test protocol Programme Segment (PS): a PS corresponds to one programme type (e.g. sport, news, drama) processed according to one of the Quality Parameters (QP) under evaluation (e.g. bit rate); each PS shoul
43、d be at least 5 minutes long. Test Session (TS): a TS is a series of one or more different combinations PSIQP without separation and arranged in a pseudo-random order. Each TS contains at least once all the PS and QP but not necessarily all the PS/QP combinations; each TS should be between 30 and 60
44、 minutes duration. Test Presentation (TP): a TP represents the full performance of a test. A TP can be divided in Test Sessions to cope with maximum duration requirements and in order to assess the quality over all the PS/QP pairs. If the number of PS/QP pairs is limited, a TP can be made of a repet
45、ition of the same Test Session to perform the test on a long enough period of time. For service quality evaluation, audio may be introduced. In this case, selection of the accompanying audio material should be considered at that same level of importance as the selection of video material, prior to t
46、he test performance. The simplest test format would use a single Programme Segment and a single Quality Parameter. A.1.1.3 Grading scales Subjects should be made aware in the test instructions that the range of travel of the handset slider mechanism corresponds to the continuous quality scale, as de
47、scribed in subclause 5.4 of ITU-R Recommendation BT.500-7. - - A.1.1.4 Observers At least fifteen subjects, non-experts, should be employed. At least 15 observers should be used. They should be non-expert, in the sense that they are not directly concerned with television picture quality as part of t
48、heir normal work, and are not experienced assessors. Prior to a session, the observers should be screened for (corrected-to-) normal visual acuity on the Snellen or Landot chart, and for normal colour vision using specially selected charts (Ishihara, for instance). The number of assessors needed dep
49、ends upon the sensitivity and reliability of the test procedure adopted and upon the anticipated size of the effect sought. A.1.1.5 Instructions to the observers In the case of services quality evaluation (with accompanying audio), observers should be instructed to consider the overall quality rather the video quality only. A.1.1.6 Test session Time duration and conditions of the test session should be those currently specified in subclause 2.7 of ITU-R Recommendation BT 500-7. A.1.1.7 Data presentation, results processing and presentat
