1、 International Telecommunication Union ITU-T J.245TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (08/2008) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Measurement of the quality of service Subjective assessment method of picture quality asse
2、ssed in the home Recommendation ITU-T J.245 Rec. ITU-T J.245 (08/2008) i Recommendation ITU-T J.245 Subjective assessment method of picture quality assessed in the home Summary Recommendation ITU-T J.245 specifies a subjective test method of picture quality assessed in the home. Picture quality is o
3、bserved at user-end in home environment on computer monitor or TV set, so only single stimulus method with subjects viewing the material once without the source reference is useful in this case. Details of single stimulus continuous quality evaluation (SSCQE) method especially adapted to observation
4、 picture quality in the home on computer or TV set screen are given in this Recommendation. Source Recommendation ITU-T J.245 was approved on 13 August 2008 by ITU-T Study Group 9 (2005-2008) under Recommendation ITU-T A.8 procedure. ii Rec. ITU-T J.245 (08/2008) FOREWORD The International Telecommu
5、nication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff
6、 questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommend
7、ations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendat
8、ion, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g., interoperability
9、 or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that complian
10、ce with the Recommendation is required of any party. 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
11、 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, ITU had not received notice of intellectual property, protected by patents, which may be required to
12、 implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2009 All rights reserved. No part of this publication may be reproduced, by
13、any means whatsoever, without the prior written permission of ITU. Rec. ITU-T J.245 (08/2008) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations 2 5 Quality of Service ranking and measurement methods for digital video services in the home . 2 5.1 Background. 2 5.2 Recommenda
14、tion 3 Annex A 7 A.1 Scope 7 A.2 Introduction 7 A.3 Calculation of mean scores. 7 A.4 Calculation of confidence interval 7 Rec. ITU-T J.245 (08/2008) 1 Recommendation ITU-T J.245 Subjective assessment method of picture quality assessed in the home 1 Scope This Recommendation specifies a subjective t
15、est method of picture quality assessed in the home. Picture quality is observed at user-end in home environment on computer monitor, or TV set (after set-top-box if needed) so only single stimulus method with subjects viewing the material once without the source reference is useful in this case. Det
16、ails of SSCQE method especially adapted to observation quality in the home on computer screen or TV set are given in this Recommendation. Laboratory subjective video quality testing seeks to separate video quality from all other variables (e.g., by using the professional quality monitor, the impact
17、of monitor is removed from subjective scores). By contrast scores from this methodology will have several variables which cannot be separated from the subjective scores (e.g., impact of consumer quality monitor, potentially distracting wall decorations in home viewing environment). This subjective m
18、ethodology is intended to more precisely analyse the viewing experience of a subject in its own home, and asks different questions than the laboratory tests. This Recommendation is intended, in particular, for network designers and operators. It gives them guidelines for network design taking into a
19、ccount technical parameters as well as the number of sustainable streams and packet rate available for video services as well as the methodology of subjective picture quality evaluation. It may be also very helpful to service providers to quantify users complaints about picture quality. The method d
20、escribed in this Recommendation is not intended to replace a subjective experiment conducted in a controlled test environment (e.g., subjective laboratory) nor regulate consumer equipments. NOTE 1 The method in this Recommendation is experimental and has not yet been validated and adequate results h
21、ave not been reviewed. Therefore, we caution the users to be careful in their use of this method. It should be also noted that the test result is not appropriate to be compared among different home test environments. NOTE 2 The structure and content of this Recommendation have been organized for eas
22、e of use by those familiar with the original source material; as such, the usual style of ITU-T Recommendations has not been applied. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommen
23、dation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other reference
24、s listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T J.241 Recommendation ITU-T J.241 (2005), Quality of service ranking an
25、d measurement methods for digital video services delivered over broadband IP networks. ITU-T Y.1540 Recommendation ITU-T Y.1540 (2002), Internet protocol data communication service IP packet transfer and availability performance parameters. 2 Rec. ITU-T J.245 (08/2008) ITU-T Y.1541 Recommendation IT
26、U-T Y.1541 (2006), Network performance objectives for IP-based services. ITU-R BT.500-11 Recommendation ITU-R BT.500-11 (2002), Methodology for the subjective assessment of the quality of television pictures. ITU-R BT.1129-2 Recommendation ITU-R BT.1129-2 (1998), Subjective assessment of standard de
27、finition digital television (SDTV) systems. ITU-R BT.1210-3 Recommendation ITU-R BT.1210-3 (2004), Test materials to be used in subjective assessment. ITU-R BT.1720 Recommendation ITU-R BT.1720 (2005), Internet protocol data communication service IP packet transfer and availability performance param
28、eters. 3 Definitions This Recommendation does not define any new terms. 4 Abbreviations This Recommendation uses the following abbreviations: IP Internet Protocol PS Program Segment QP Quality Parameter SSCQE Single Stimulus Continuous Quality Evaluation TP Test Presentation TS Test Session 5 Qualit
29、y of Service ranking and measurement methods for digital video services in the home 5.1 Background Digital transport streams based on MPEG-2 encoding have become the prevailing technology for augmenting the experience of digital television services, since it allows combining the distribution of high
30、 quality digital television services with the opportunity for end users to enjoy real-time interaction with multimedia service platforms. This Recommendation is dealing with subjective assessment of picture quality delivered to the home by air, cable, satellite as well as over IP networks. Special a
31、ttention is given on the latest one because it is a new service and assessing in the home is one possible method for service evaluation. The broadband fixed communication networks start to be extensively deployed in several countries thus clear opportunities emerge for extending this offer through t
32、ransport based on IP protocols. The native shared-access and bidirectional capabilities of an IP network, in fact, offer an ideal environment for providing customers with full end-user interactivity and support for advanced services; this offers advantages over traditional video streaming services.
33、IP-based broadband communication networks thus provide another high-performance, bidirectional transport environment to transparently convey digital video content. There are two possibilities of video content observation at the user-end. Observations can be carried out: on stationary or mobile compu
34、ter monitor or, (in the case of using the home set-top-box, if needed) on the TV set screen. The picture quality delivered over IP networks depends on many factors, such as: source quality, Rec. ITU-T J.245 (08/2008) 3 network parameters and network end-to-end bandwidth occupancy, a signal processin
35、g and performance of a display device. The source quality depends on: method of coding, picture definition and signal bit rate, which are closely connected together. For preserving a good picture quality when picture definition is higher, the bit rates also have to be higher, for example: Picture de
36、finition Bit rate Frame/ps 192x144 (24 to 52) kbit/s 12.5 192x144 141 kbit/s 12.5 384x288 273 kbit/s 12.5 384x288 (331 to 755) kbit/s 25 704x576 1119 kbit/s 25 The noise introduced in IP packet networks is described by the following parameters: packet loss ratio, latency, jitter (latency variation).
37、 When the good quality video content is introduced into the network according to the maximum end-to-end bandwidth and the packet rate available for video services, the network parameters required for preserving a good quality of the image should have values outlined and motivated in ITU-R BT.1720. T
38、he recommended objective measurement methods of the above parameters are also given in this Recommendation. Each IP transport network should have defined maximum bandwidth per stream or packet rate for a given packet size, maximum packet rate per stream and maximum number of sustainable streams. The
39、 determination of the service quality, based on end-to-end measurements should provide the information on picture quality offered to the user. It depends to a high degree on network occupancy. If, in a network with a defined packet rate per stream, the number of sustainable streams by other services
40、 is too high, the service quality will be poor or not available. This Recommendation deals with subjective picture quality assessment at the user end in home on standby or mobile computer monitor as well as on TV set screen. Conventional methods of laboratory testing do not replicate these condition
41、s. It was considered useful, therefore, for the subjective quality of video delivered over IP networks to be measured continuously with subject viewing the material once without a source reference as in single stimulus method (SSCQE) but with some modifications resulted from specific service. This m
42、ethod is expected to be as good as the laboratory method, but has different goals. SSCQE was chosen as the basis of this Recommendation (e.g., rather than the absolute category rating (ACR) methodology), because SSCQE is a continuous quality method and can be used for longer test sequences. That is,
43、 in SSCQE as with home television viewing, video is presented continuously, without breaks between content. 5.2 Recommendations 5.2.1 Viewing conditions Measurements will be made at different networks user-ends in home environment. Viewing conditions should be chosen to be similar to, but not more c
44、ritical than, typical conditions in home environment given in ITU-R BT.1129-2. 4 Rec. ITU-T J.245 (08/2008) Condition Item Values a Ratio of viewing distance to picture height 6 (Note)b Peak luminance 200 cd/m c Environmental Illuminance on the screen (Incident light from the environment falling on
45、the screen should be measured perpendicularly on the screen) 200 Lux NOTE Other viewing environment variables are intentionally uncontrolled (e.g., wall colour). Reflections on the viewing screen should be avoided and the monitor should be set with the proper aspect ratio. 5.2.2 Observers In princip
46、le, 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 their normal work, and are not experienced assessors (see Note). Prior to a session, the observers should be screened for (corrected-to-) normal vi
47、sual acuity and for normal colour vision using specially selected charts. When estimations are made on computer screen, the number of simultaneous assessors may be 1 to 3 people at the same time, depending on the room and screen size. All observers should watch in the same conditions because reprodu
48、ced colour and brighness may change according to the viewing position. Computer screen resolution and brightness should be the same in all test presentation and should be given in test protocol. Identical test sessions should be performed with all observers. That is, this identical session should be
49、 performed in the same place using the same test computer and on the same test material stored in computer memory. NOTE Preliminary findings suggest that non-expert observers may yield more critical results with exposure to higher quality transmission and display technologies. 5.2.3 Instruction for the observers Assessors should be carefully introduced to the method of assessment, the types of impairment or quality factors likely to occur, the grading scale, timing, etc. Training sequences demonstrating the range and the type of the impairments to be as
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