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VQuad-HD

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VQuad-HD (Objective perceptual multimedia video quality measurement of HDTV) is a video quality testing technology for high definition video signals. VQuad-HD™ was selected as the new ITU-T video quality standard - known as J.341[1] - for high definition television video signals. The new VQuad-HD™ algorithm was developed by Swissqual in 2008-2010. It was the best performing model in the HDTV competition to find the new standard that was organized by the independent and non-commercial Video Quality Expert Group (VQEG). However, it was not compared with leading video quality models outside of the tested competing proponents

J.341 Recommendation 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 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.

It is generally accepted that full reference (FR) methods provide the most accurate perceptual picture quality measurements. However, a reference video signal is required, otherwise a no-reference model is required. 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 ITU-T P.910.

Unfortunately, following standardization, the VQuad-HD model has found little commercial use. Commercial picture quality systems used by the Television industry are currently dominated by methods that use the Structural Similarity (SSIM) model, the MOVIE Index, and the Tektronix PQA line of systems.

Applications scope

There are four major areas where this standard can have impact:

  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.
Alt text
VQuad-HD flowchart

Overview of the model

The model predicts the video quality as it is perceived by subjects (viewers). The prediction model uses psycho-visual and cognitive inspired modelling to emulate subjective perception. It compares the high quality reference video and the associated degraded video sequence under test. The estimation process is based on the following steps:

  1. Preprocessing of the video sequences in particular, noise removal and sub-sampling
  2. Temporal and spatial alignment between reference and processed video sequence
  3. Analysis of the local similarity and difference feature
  4. Computation of the global spatial degradation
  5. Evaluation of the global temporal degradation by evaluating motion intensity
  6. The quality score MOS is estimated based on a non-linear aggregation of the above features

Video formats/codecs

The objective model is tested on a wide variety of different frame-rates as used in TV applications (29.97fps and 25fps), in Interlaced video and Progressive scan mode at the resolution 1080 x 1920. Content of 720 x 1280 was included in testing by up-sampling it to 1080 x 1920, as this is the typical case for most consumer applications. Content with 24fps was included in testing but re-played at 25fps.

Videos encoded by H.264/MPEG-4 AVC [2] using either high or main profile, or MPEG-2 [3] are supported. This objective model is deemed appropriate for telecommunication services delivered at between 1 Mbit/s and 30 Mbit/s.

Transmission impairments

The types of errors handled by model include packet errors (both IP and MPEG transport stream) such as Packet loss,[4] Packet delay variation, Jitter, overflow and underflow, bit errors, and over-the-air transmission errors.

Standardisation and validation

VQuad-HD™ was the best performing model in the HDTV competition that was organized by the independent and non-commercial Video Quality Expert Group (VQEG).[5] VQEG then proposed VQuad-HD model to ITU-T to form the new video quality standard - known as J.341, which happened in January 2011.

See also

References

  1. ^ "ITU-T J.341, Objective perceptual multimedia video quality measurement of HDTV for digital cable television in the presence of a full reference". Retrieved 2011-01-20.
  2. ^ "The H.264/AVC Advanced Video Coding Standard: Overview and Introduction to the Fidelity Range Extensions" (PDF). Retrieved 2011-07-30.
  3. ^ "MPEG-2 Transport Stream". AfterDawn.com. Retrieved 2010-06-08.
  4. ^ "Packet loss or latency at intermediate hops" (HTTP). Retrieved 2007-02-25.
  5. ^ "Report on the Validation of Video Quality Models for High Definition Video Content" (ZIP). Retrieved 2010-07-01.
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