1、 International Telecommunication Union ITU-T J.341TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2011) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Measurement of the quality of service Objective perceptual multimedia video quality measur
2、ement of HDTV for digital cable television in the presence of a full reference Recommendation ITU-T J.341 Rec. ITU-T J.341 (01/2011) i Recommendation ITU-T J.341 Objective perceptual multimedia video quality measurement of HDTV for digital cable television in the presence of a full reference Summary
3、 Recommendation ITU-T J.341 provides an objective perceptual video quality measurement method for HDTV when a full reference signal is available. The following list shows example applications that can use this Recommendation: 1) Potentially real-time, in-service quality monitoring at the source. 2)
4、Remote destination quality monitoring when a copy of the source is available at the point of measurement. 3) Quality measurement for monitoring of a storage or transmission system that utilizes video compression and decompression techniques, either a single pass or a concatenation of such techniques
5、. 4) Lab testing of video systems. This Recommendation includes an electronic attachment containing several short high definition (HD) video sequences, their corresponding predicted mean opinion scores (MOS), and the predicted MOS for five HD databases available via VQEG. History Edition Recommendat
6、ion Approval Study Group 1.0 ITU-T J.341 2011-01-13 9 ii Rec. ITU-T J.341 (01/2011) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Stand
7、ardization 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 basis. The World Telecommunication Standardization Assembly (WTSA), wh
8、ich meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations 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
9、ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendat
10、ion is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability 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 “
11、must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance 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
12、 may involve the use of a claimed Intellectual Property Right. ITU 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
13、this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to 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 datab
14、ase at http:/www.itu.int/ITU-T/ipr/. ITU 2011 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T J.341 (01/2011) iii Table of Contents Page 1 Scope 1 1.1 Application . 2 1.2 Limitations 2 2 References.
15、2 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 3 4 Abbreviations and acronyms 3 5 Conventions 3 6 Description of the full reference methodology . 4 7 Findings of the Video Quality Experts Group (VQEG) . 5 Annex A Model description 6 A.1 Preprocessing 7 A.2
16、 Time alignment . 8 A.3 Spatial frame alignment 9 A.4 Computation of local similarity and local difference features . 10 A.5 Analysis of the distribution of local features 10 A.6 Computation of the blockiness feature . 12 A.7 Computation of the jerkiness feature (temporal quality) 13 A.8 Aggregation
17、 to MOS 15 A.9 Handling of heavily spatially misaligned video sequences 20 A.10 Reference source code implementation 21 Annex B Conformance testing 22 Bibliography. 23 Electronic attachment: HD video sequences and predicted MOSs. Rec. ITU-T J.341 (01/2011) 1 Recommendation ITU-T J.341 Objective perc
18、eptual multimedia video quality measurement of HDTV for digital cable television in the presence of a full reference 1 Scope This Recommendation1provides a perceptual video quality measurement method for use in high definition television (HDTV) non-interactive applications when the full reference (F
19、R) measurement method can be used. The model was developed to estimate subjective quality scores obtained using b-ITU-T P.910. The full reference measurement method can be used when the unimpaired reference video signal is readily available at the measurement point, as may be the case of measurement
20、s on individual equipment or a chain in the laboratory or in a closed environment such as a cable television head end. The estimation method includes both calibration and objective video quality estimations. The validation test material contained both b-ITU-T H.264 and MPEG-2 coding degradations and
21、 various transmission error conditions (e.g., bit errors, dropped packets). The model proposed in this Recommendation may be used to monitor the quality of deployed networks to ensure their operational readiness. The visual effects of the degradations may include spatial as well as temporal degradat
22、ions. The model in this Recommendation can also be used for lab testing of video systems. When used to compare different video systems, it is advisable to use a quantitative method (such as that in b-ITU-T J.149) to determine the models accuracy for that particular context. This Recommendation is de
23、emed appropriate for telecommunication services delivered at between 1 Mbit/s and 30 Mbit/s. The following resolutions and frame rates were considered in the validation test: 1080i 60 Hz (29.97 fps) 1080p (25 fps) 1080i 50 Hz (25 fps) 1080p (29.97 fps) The following conditions were allowed in the va
24、lidation test for each resolution: Test factors Video resolution: 1920x1080 interlaced and progressive Video frame rates 29.97 and 25 frames per second Video bitrates: 1 to 30 Mbit/s Temporal frame freezing (pausing with skipping) of maximum 2 seconds Transmission errors with packet loss Conversion
25、of the SRC from 1080 to 720p, compression, transmission, decompression, and then conversion back to 1080. Coding technologies ITU-T H.264/AVC (MPEG-4 Part 10) MPEG-2 _ 1This Recommendation includes an electronic attachment containing several short high definition (HD) video sequences, their correspo
26、nding predicted mean opinion scores (MOS), and the predicted MOS for five HD databases available via VQEG. 2 Rec. ITU-T J.341 (01/2011) Note that 720p was considered in the validation test plan as part of the test condition (HRC). Because currently 720p is commonly up-scaled as part of the display,
27、it was felt that 720p HRCs would more appropriately address this format. 1.1 Application The applications for the estimation model described in this Recommendation include, but are not limited to: 1) Potentially real-time, in-service quality monitoring at the source. 2) Remote destination quality mo
28、nitoring when a copy of the source is available at the point of measurement. 3) Quality measurement for monitoring of a storage or transmission system that utilizes video compression and decompression techniques, either a single pass or a concatenation of such techniques. 4) Lab testing of video sys
29、tems. 1.2 Limitations The video quality estimation model described in this Recommendation cannot be used to replace subjective testing. Correlation values between two carefully designed and executed subjective tests (i.e., in two different laboratories) normally fall within the range 0.95 to 0.98. I
30、f this Recommendation is utilized to make video system comparisons (e.g., comparing two codecs), it is advisable to use a quantitative method (such as that in b-ITU-T J.149) to determine the models accuracy for that particular context. When frame freezing was present, the test conditions typically h
31、ad frame freezing durations less than two seconds. The model in this Recommendation was not validated for measuring video quality in a re-buffering condition (i.e., video that has a steadily increasing delay or freezing without skipping). The model was not tested on other frame rates than those used
32、 in TV systems (i.e., 29.97 frames per second and 25 frames per second, in interlaced or progressive mode). It should be noted that in case of new coding and transmission technologies producing artifacts which were not included in this evaluation, the objective model may produce erroneous results. H
33、ere, a subjective evaluation is required. Note that the model in this Recommendation was not evaluated on talking-head content typical of video-conferencing scenarios. 2 References This Recommendation does not incorporate any normative provisions from external references. 3 Definitions 3.1 Terms def
34、ined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 subjective assessment (picture) b-ITU-T J.144: The determination of the quality or impairment of programme-like pictures presented to a panel of human assessors in viewing sessions. 3.1.2 objective perceptual measur
35、ement (picture) b-ITU-T J.144: The measurement of the performance of a programme chain by the use of programme-like pictures and objective (instrumental) measurement methods to obtain an indication that approximates the rating that would be obtained from a subjective assessment test. Rec. ITU-T J.34
36、1 (01/2011) 3 3.1.3 proponent b-ITU-T J.144: An organization or company that proposes a video quality model for validation testing and possible inclusion in an ITU Recommendation. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 frame rate: The number o
37、f unique frames (i.e., total frames repeated frames) per second. 3.2.2 simulated transmission errors: Errors imposed upon the digital video bit stream in a highly controlled environment. Examples include simulated packet loss rates and simulated bit errors. Parameters used to control simulated trans
38、mission errors are well defined. 3.2.3 transmission errors: Any errors imposed on the video transmission. Example types of errors include simulated transmission errors and live network conditions. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: ACR Abs
39、olute Category Rating ACR-HR Absolute Category Rating with Hidden Reference AVI Audio Video Interleave DMOS Difference Mean Opinion Score FR Full Reference FRTV Full Reference Television HRC Hypothetical Reference Circuit ILG VQEGs Independent Laboratory Group MOS Mean Opinion Score MOSp Mean Opinio
40、n Score, predicted NR No (or zero) Reference PSNR Peak Signal-to-Noise Ratio PVS Processed Video Sequence RMSE Root Mean Square Error RR Reduced Reference SFR Source Frame Rate SRC Source Reference Channel or Circuit VQEG Video Quality Experts Group 5 Conventions This Recommendation uses the followi
41、ng convention: YUV Color Space and file format 4 Rec. ITU-T J.341 (01/2011) 6 Description of the full reference methodology The double-ended measurement method with full reference, for objective measurement of perceptual video quality, evaluates the performance of systems by making a comparison betw
42、een the undistorted input, or reference, video signal at the input of the system, and the degraded signal at the output of the system (Figure 6-1). Figure 6-1 shows an example of application of the full reference method to test a codec in the laboratory. Figure 6-1 Application of the full reference
43、perceptual quality measurement method to test a codec in the laboratory The comparison between input and output signals may require a temporal alignment or a spatial alignment process, the latter to compensate for any vertical or horizontal picture shifts or cropping. It also may require correction
44、for any offsets or gain differences in both the luminance and the chrominance channels. The objective picture quality rating is then calculated, typically by applying a perceptual model of human vision. Alignment and gain adjustment is known as registration. This process is required because most ful
45、l reference methods compare reference and processed pictures on what is effectively a pixel-by-pixel basis. The video quality metrics described in Annexes A and B include registration methods. As the video quality metrics are typically based on approximations to human visual responses, rather than o
46、n the measurement of specific coding artefacts, they are in principle equally valid for analogue systems and for digital systems. They are also in principle valid for chains where analogue and digital systems are mixed, or where digital compression systems are concatenated. Figure 6-2 shows an examp
47、le of the application of the full reference method to test a transmission chain. Figure 6-2 Application of the full reference perceptual quality measurement method to test a transmission chain Rec. ITU-T J.341 (01/2011) 5 In this case, a reference decoder is fed from various points in the transmissi
48、on chain, e.g., the decoder can be located at a point in the network, as in Figure 6-2, or directly at the output of the encoder, as in Figure 6-1. If the digital transmission chain is transparent, the measurement of objective picture quality rating at the source is equal to the measurement at any s
49、ubsequent point in the chain. It is generally accepted that the full reference method provides the best accuracy for perceptual picture quality measurements. The method has been proven to have the potential for high correlation with subjective assessments made in conformity with the ACR-HR methods specified in b-ITU-T P.910. 7 Findings of the Video Quality Experts Group (VQEG) Studies of perceptual video quality measurements are conducted in an informal group, called the Video Quality Experts Group (VQEG), which reports
