ITU-T J.341 PDF

This Recommendation¹ provides a perceptual video quality measurement method for use in high definition television (HDTV) non-interactive applications when the full reference (FR) 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 measurements 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 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 degradations. 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 model's accuracy for that particular context.

This Recommendation is deemed 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)

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, it was felt that 720p HRCs would more appropriately address this format.

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 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.

4) Lab testing of video systems.

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. If 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 model's accuracy for that particular context.

When frame freezing was present, the test conditions typically had 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 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. Here, a subjective evaluation is required.

Note that the model in this Recommendation was not evaluated on talking-head content typical of video-conferencing scenarios.

1 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.