1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU J.143 (OW O0 O) SERIES J: TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Measurement of the quality of service User requirements for objective perceptual video quality measurements i
2、n digital cable television ITU-T Recommendation J. 143 (Formerly CC ITT Recommendation) ITU-T J-SERIES RECOMMENDATIONS TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS General Recommendations General specifications for analogue sound-programme transmission Performance charact
3、eristics of analogue sound-programme circuits Equipment and lines used for analogue sound-programme circuits Digital encoders for analogue sound-programme signais Digital transmission of sound-programme signals Circuits for analogue television transmission Analogue television transmission over metal
4、lic lines and interconnection with radio-relay links Digital transmission of television signals Ancillary digital services for television transmission Operational requirements and methods for television transmission Interactive systems for digital television distribution Transport of MPEG-2 signals
5、on packetised networks Measurement of the quality of service Digital television distribution through local subscriber networks J. 1-J.9 J. 10-J. 19 J.20-J.29 5.30-5.39 J.40-J.49 J.50-J.59 J.60-J.69 5.70-5.79 J.80-J.89 J.90-J.99 J. 100-J. 109 J.110-J.129 J.130-J.139 J.14O-J.149 J. 150-J.159 lfi For f
6、urther details, please refer to the list of ITU-TRecommendations. ITU-T Recommendation 5.143 User requirements for objective perceptual video quality measurements in digital cable television Summary This Recommendation describes user requirements for objective perceptual video quality measurements i
7、n digital cable television and similar applications. Source ITU-T Recommendation J. 143 was prepared by ITU-T Study Group 9 (1 997-2000) and approved under the WTSC Resolution 1 procedure on 18 May 2000. FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agenc
8、y in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide b
9、asis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topic s. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSC
10、Resolution 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 for conciseness to indicate both a telecommunication administra
11、tion and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicabilit
12、y 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, ITU had not received notice of intellectual property, protected by patents, which may be required to implement th
13、is 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 ITU 2001 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electr
14、onic or mechanical, including photocopying and microfilm, without permission in writing fi-om ITU. CONTENTS 1 2 2.1 2.2 3 4 4.1 4.2 4.3 4.4 4.5 5 Scope References Normative References Informative References . Terms. definitions and acronyms . User requirements . Accuracy of perceptual video quality
15、measurements . Availability of the inputheference video signal . In-service operation Potential applications and related considerations . Standardization and proprietary solutions Objective measurement of perceptual video quality Page 1 1 1 1 1 2 2 2 2 2 3 3 . . Appendix I Measurement methodology 4
16、I 1 Methodology using the full video reference 4 1.2 Methodology using reduced reference information 5 1.3 Methodology using no reference signal 5 . . . . Introduction Digital television produces new Quality of Services considerations, with complex relationships between objective parameter measureme
17、nts and subjective picture quality. Objective measurements with good correlation to subjective quality assessment are desirable in order to attain optimal quality of service in the operation of cable television systems. ITU-T Recommendation 5.143 User requirements for objective perceptual video qual
18、ity measurements in digital cable television 1 Scope This Recommendation describes users requirements for objective measurements of perceptual video quality in digital video systems used in cable television and in similar applications. Such objective perceptual video quality measurements may be requ
19、ired for several applications, as described below. - To measure the end-to-end performance of digital cable television systems from the signal source to the users receiver. In this application the transmission chain includes the cable distribution system and may also include the satellite links, ter
20、restrial links andor broadband network links that provide source signals to the cable head-end. To measure the performance of a section of the total chain, which is sufficiently limited to be equipped with auxiliary measurement devices at appropriate points along the section under test. To measure t
21、he performance of single pieces of equipment (e.g. codecs) or of local chains of equipment in a laboratory or at the cable head-end premises. - - 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of t
22、his 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 recent edition of the Recommendations and othe
23、r references listed below. A list of the currently JTU-T Recommendations is regularly published. Normative References ITU-R BT.500-10 (2000), Methodology for the subjective assessment of the quality of television pictures. Informative References ITU-T J. 140 (1 998), Subjective picture quality asses
24、sment for digital cable television systems. ITU-T P.91 O (1 999), Subjective video quality assessment methods for multimedia applications. Terms, definitions and acronyms See ITU-T J.l. This Recommendation does not use any unusual terms or abbreviations. 4 User requirements 4.1 This requirement rela
25、tes to the need for accurate measurements of perceptual video quality on programme material that is delivered by cable television, in spite of the great variety of its content and of its impairments. The proposed perceptual measurement device should ideally provide an accurate measurement of percept
26、ual video quality in normal broadcast/cablecast operation, irrespective of the programme content, of the digital encoding used for programme material, of the composition and performance of the transmission chain and of the compression ratio used. Measurements should closely match the average scores
27、that would be obtained from formal subjective assessment tests, performed by an independent laboratory or organisation in accordance with ITU-R BT.500. This should be true for a large set of still and moving test pictures, under various degrees of different distortions. Accuracy of perceptual video
28、quality measurements 4.2 Measurements of perceptual video quality may be needed both within a laboratory or a cable television head-end, and over larger parts of the cable television chain, or even over the whole chain. Measurements within a laboratory, or within a cable head-end (e.g. from the head
29、-end input signal to its output to the cable distribution network) obviously would benefit fi-om the availability of the input video signal at the measurement point. In other cases, when a larger part of the delivery chain needs to be measured (e.g. from the head-end input to the users receiver) the
30、 input video signal would not normally be available. In those cases, perceptual video quality measurements may be performed with the assistance of reference data that travels with the programme signal and represents perceptual video quality measured at an upstream point, or in the total absence of a
31、ny reference signal or data (See Appendix I). Availability of the inputheference video signal 4.3 In-service operation There are applications where it is required that the perceptual measuring device should be capable of operating on-line in a cable television system; in this case the insertion of t
32、he measurement device in the chain should not adversely affect the performance of the chain. 4.4 There are at least two distinct applications in which a cable television operator may wish to perform objective measurements of perceptual video quality. - One application is to perform objective laborat
33、ory tests of perceptual video quality on new equipment, e.g. equipment that is considered for possible purchase. In this case, it would generally be possible to use a full reference, and emphasis would likely be placed on perceptual measurement accuracy. It would generally be recognised and accepted
34、 that the greater the required measurement accuracy, the more complex the perceptual model might be, and the longer the computation time required for each measurement. Another application is to install perceptual measuring devices along the programme chain, in order to monitor its performance on-lin
35、e. In this case emphasis would likely be placed on measurement reliability and on measurement time, since the measurement devices would need to operate around the clock with little maintenance, and they would be expected to provide indications on quasi-real time. It would also generally be accepted
36、that the measurement devices should operate without a full reference, i.e. with assistance data or Potential applications and related considerations - even without it. Care should be taken in sub-sampling due to the transient nature of impairments in digital video systems, especially in the presence
37、 of transmission errors. There is certainly a requirement to perform objective measurements of perceptual video quality on line and in real time in a cable television network. At this moment however the speed of computation of perceptual video quality might still be too high when a sufficiently comp
38、lex perceptual quality model is used, and a compromise should likely be found between the measurement accuracy and its speed. This may be provided by measurement of specific picture impairments (such as MPEG Blockiness) that can be related to perceptual video quality. There will also likely be a nee
39、d to perform objective measurements of perceptual video quality for a selected group of programs contained within one or more multiplexes. In this case the perceptual picture quality of the individual programme streams in the group can be expected to vary from moment to moment as a function not only
40、 of the individual stream content but also of the content of the other streams in the group and of statistical multiplexing. The way in which the perceptual video quality readings for the various individual streams should be combined in order to obtain a reading applicable to the group is currently
41、under study. Standardization and proprietary solutions The development of complex and accurate perceptual quality models and the verification of their accuracy requires an important research effort, and it is natural that, while some researchers and manufacturers will be willing to share the details
42、 of their method, other manufacturers will be reluctant to do so, or to accept to license them to other manufacturers on an equitable and non- discriminatory basis, as is required by the ITU Patent Policy. It should be stressed that it will not be possible for the ITU to recommend the use of the tec
43、hnology developed by those manufacturers who are not willing to abide by the ITU Patent Policy, and who insist that the details of their method should continue to remain their own property. This situation would be regrettable, as it would harm the interests of broadcasters and cablecasters, emore, t
44、here is a risk that, if the details of a method are proprietary, its manufacturer may ce those enhancements that may become possible from time to time, with the result that ent from some manufacturer may no longer conform with the equipment of the same brand del that has been tested and certified by
45、 independent international bodies, and it may provide t degree of accuracy (better or worse). In this circumstance it might become impossible to compare results of perceptual quality tests performed by different laboratories or operators, since the results might have been obtained using different ge
46、nerations of a proprietary perceptual model. those of the whole market. 5 Objective measurement of perceptual video quality It is?recommended that cable television operators and laboratories should perform objective tests of perceptual video quality using the method that best meets their needs (comp
47、lete reference, partial reference or no reference) bearing in mind the information provided in this Recommendation. It is also recommended that, when performances and applications are comparable, users of perceptual quality measurement devices should take into account the caveats recalled in 4.5, in
48、 the choice of the equipment appropriate to their needs. Additional Recommendations on perceptual video quality measurements will be issued as soon as sufficient evidence is available on the characteristics and performance of the different measurement methods currently offered on the market or under
49、 study. APPENDIX I Measurement methodology This appendix is intended to provide a more comprehensive description of the three main measurement methodologies for the objective measurement of perceptual video quality. They offer different approaches that provide differing levels of measurement accuracy, and require different information regarding the inputheference video. 1.1 One way to evaluate the performance of systems is to make a comparison between the input or reference video at the input of the system, and the processed signal at the output of the system. (Figures 1.1 and 1.2). The c
