1、 International Telecommunication Union ITU-T J.342TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (04/2011) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Measurement of the quality of service Objective multimedia video quality measurement of HD
2、TV for digital cable television in the presence of a reduced reference signal Recommendation ITU-T J.342 Rec. ITU-T J.342 (04/2011) i Recommendation ITU-T J.342 Objective multimedia video quality measurement of HDTV for digital cable television in the presence of a reduced reference signal Summary R
3、ecommendation ITU-T J.342 provides an objective video quality measurement method for high definition television (HDTV) when a reduced reference signal is available. The following list shows example applications that can use this Recommendation: 1) Interlaced video television streams over cable netwo
4、rks including those transmitted over the Internet using Internet Protocol. 2) Video quality monitoring at the receiver when side-channels are available. 3) Video quality monitoring at measurement nodes located between point of transmission and point of reception. History Edition Recommendation Appro
5、val Study Group 1.0 ITU-T J.342 2011-04-29 9 ii Rec. ITU-T J.342 (04/2011) 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 Standardizatio
6、n 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), which meets
7、 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 ITU-Ts pu
8、rview, 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 Recommendation is vo
9、luntary. 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 “must“ and
10、 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 may invo
11、lve 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 this Reco
12、mmendation, 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 database at ht
13、tp:/www.itu.int/ITU-T/ipr/. ITU 2012 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.342 (04/2011) iii Table of Contents Page 1 Scope 1 1.1 Applications 2 1.2 Limitations 2 2 References. 2 3 Defini
14、tions 3 3.1 Terms defined elsewhere 3 3.2 Terms defined in this Recommendation . 3 4 Abbreviations and acronyms 3 5 Conventions 4 6 Description of the reduced reference measurement methods . 4 6.1 Introduction 4 6.2 EPSNR reduced-reference model . 5 Appendix I Findings of the Video Quality Experts G
15、roup (VQEG) 17 Bibliography. 19 Rec. ITU-T J.342 (04/2011) 1 Recommendation ITU-T J.342 Objective multimedia video quality measurement of HDTV for digital cable television in the presence of a reduced reference signal 1 Scope This Recommendation provides a video quality measurement method for use in
16、 high definition television (HDTV) non-interactive applications when the reduced reference (RR) measurement method can be used. The model was compared to subjective quality scores obtained using b-ITU-T P.910. Analyses showed that the accuracy of this model was equivalent to that of peak signal-to-n
17、oise ratio (PSNR). For the RR model to operate correctly, the unimpaired source video should be available for the model to extract parameters. These extracted parameters as well as the degraded video sequence are the inputs to the RR model. The estimation method performs both calibration (i.e., gain
18、/offset and spatial/temporal registration) and objective video quality estimation. The validation test material contained both ITU-T H.264 and MPEG-2 coding degradations and various transmission error conditions (e.g., bit errors, dropped packets). The model proposed in this Recommendation may be us
19、ed 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 degradations. The model in this Recommendation can also be used for lab testing of video systems. When used to compare different video
20、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 deemed appropriate for telecommunication services delivered between 1 Mbit/s and 30 Mbit/s. The following resolutions and frame r
21、ates 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 validation test for each resolution: Test factors Video resolution: 1920 1080 interlaced and progressive Video frame rates 29.97
22、 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 of the SRC from 1080 to 720p, compression, transmission, decompression, and then conversion back to 1080 Coding technologies I
23、TU-T H.264/AVC (MPEG-4 Part 10) MPEG-2 2 Rec. ITU-T J.342 (04/2011) Note that 720p was considered in the validation test plan as part of the test condition of the hypothetical reference circuit (HRC). Because currently 720p is commonly upscaled as part of the display, it was felt that 720p HRCs woul
24、d more appropriately address this format. 1.1 Applications The applications for the estimation models described in this Recommendation include but are not limited to: 1) Interlaced video television streams over cable networks including those transmitted over the Internet using Internet Protocol. 2)
25、Video quality monitoring at the receiver when side-channels are available. 3) Video quality monitoring at measurement nodes located between point of transmission and point of reception. The model described in this Recommendation provides a statistically similar performance to PSNR; yet it can be use
26、d for video quality assessment when the reference signal is not available at the point of measurement. 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 subj
27、ective tests (i.e., in two different laboratories) normally fall within the range 0.95 to 0.98. This Recommendation cannot be used to make video system comparisons (e.g., comparing two codecs, comparing two different implementations of the same compression algorithm). The performance of the video qu
28、ality estimation model described in this Recommendation is not statistically better than PSNR. When frame freezing was present, the test conditions typically had frame freezing durations for less than 2 seconds. The model in this Recommendation was not validated for measuring video quality in a re-b
29、uffering 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 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
30、 of new coding and transmission technologies producing artifacts which were not included in this evaluation, the objective model may produce erroneous results. Here, a subjective evaluation is required. Note that the model in this Recommendation was not evaluated on talking-head content typical of v
31、ideo-conferencing scenarios. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other refe
32、rences 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 references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference
33、 to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T J.144 Recommendation ITU-T J.144 (2004), Objective perceptual video quality measurement techniques for digital cable television in the presence of a full reference. Rec. ITU-T
34、 J.342 (04/2011) 3 ITU-T J.244 Recommendation ITU-T J.244 (2008), Full reference and reduced reference calibration methods for video transmission systems with constant misalignment of spatial and temporal domains with constant gain and offset. 3 Definitions 3.1 Terms defined elsewhere This Recommend
35、ation uses the following terms defined elsewhere: 3.1.1 objective perceptual measurement (picture) 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
36、 rating that would be obtained from a subjective assessment test. 3.1.2 proponent ITU-T J.144: An organization or company that proposes a video quality model for validation testing and possible inclusion in an ITU Recommendation. 3.1.3 subjective assessment (picture) ITU-T J.144: The determination o
37、f the quality or impairment of programme-like pictures presented to a panel of human assessors in viewing sessions. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 frame rate: The number of unique frames (i.e., total frames repeated frames) per second.
38、 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 transmission errors are well defined. 3.2.3 transmission errors: Any
39、error 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 Absolute Category Rating (see b-ITU-T P.910) ACR-HR Absolute Categor
40、y Rating with Hidden Reference (see b-ITU-T P.910) 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 Opinion Score, predicted NR No
41、(or zero) Reference PSNR Peak Signal-to-Noise Ratio PVS Processed Video Sequence 4 Rec. ITU-T J.342 (04/2011) RMSE Root Mean Square Error RR Reduced Reference SFR Source Frame Rate SRC Source Reference Channel (or Circuit) VQEG Video Quality Experts Group YUV Colour Space and file format 5 Conventio
42、ns None. 6 Description of the reduced reference measurement methods 6.1 Introduction Although PSNR has been widely used as an objective video quality measure, it is also reported that it does not well represent perceptual video quality. By analysing how humans perceive video quality, it is observed
43、that the human visual system is sensitive to degradation around the edges. In other words, when the edge pixels of a video are blurred, evaluators tend to give low scores to the video even though the PSNR is high. Based on this observation, the reduced reference models which mainly measure edge degr
44、adations have been developed. Figure 6-1 illustrates how a reduced-reference model works. Features which will be used to measure video quality at a monitoring point are extracted from the source video sequence and transmitted. Table 6-1 shows the side-channel bandwidths for the features, which have
45、been tested in the VQEG HDTV test. transmitterreceiversourcevideosequencechannelreceivedvideosequenceRRmodelfeatureextractionforvideo qualitymeasurementchannelFigure 6-1 Block diagram of reduced-reference model Table 6-1 Side-channel bandwidths Video format Tested bandwidths 1080i 60 Hz (29.97 fps)
46、1080p (29.97 fps) 56 kbit/s, 128 kbit/s, 256 kbit/s 1080p (25 fps) 1080i 50 Hz (25 fps) 56 kbit/s, 128 kbit/s, 256 kbit/s Rec. ITU-T J.342 (04/2011) 5 6.2 EPSNR reduced-reference model 6.2.1 Edge PSNR (EPSNR) RR models mainly measure on-edge degradations. In the models, an edge detection algorithm i
47、s first applied to the source video sequence to locate the edge pixels. Then, the degradation of those edge pixels is measured by computing the mean squared error. From this mean squared error, the edge PSNR is computed. Any edge detection algorithm can be used, though there may be minor differences
48、 in the results. For example, any gradient operator to locate edge pixels can be used from the number of gradient operators that have been proposed. In many edge detection algorithms, the horizontal gradient image ghorizontal(m,n) and the vertical gradient image gvertical(m,n) are first computed usi
49、ng gradient operators. Then, the magnitude gradient image g(m,n) may be computed as follows: nullnullnull,nullnull null |nullnullnullnullnullnullnullnullnullnullnullnullnull,nullnull|null |nullnullnullnullnullnullnullnullnullnullnull,nullnull| Finally, a thresholding operation is applied to the magnitude gradient image to find edge pixels. In other words, pixels whose magnitude gradients exceed a threshold value are considered as edge pixels. Figures 6-2 to 6-6 illustrate the procedure. Figure 6-2 shows a source image. Figure 6-3 shows a horiz
