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Question 19

​​​Objective and subjective methods for evaluating perceptual audiovisual quality in multimedia and television services

(Continuation of Question 12/9 - Objective and subjective methods for evaluating perceptual audiovisual quality in multimedia services within the terms of Study Group 9 & Continuation of Question 2/9 - Measurement and control of the end-to-end quality of service (QoS) for advanced television technologies, from image acquisition to rendering, in contribution, primary distribution and secondary distribution networks)

In digital transmission systems, the perceptual quality of the audiovisual signal is influenced by a number of interacting factors, such as source coding and compression, bit rate (fixed or variable), delay, bandwidth, synchronization between the media, transmission impairments, and many others. New services that use IP, wireless, mobile, NGN, etc. are providing ubiquitous access for multimedia services. Audiovisual multimedia cover multichannel audio, television, and 3D video applications including interactive ones, in addition to other applications such as videoconferencing, personal computer desktop conferencing, interactive educational and training services, groupware, interactive gaming, and videotelephony. This Question focuses on perceptual impacts of compression, transmission, and decompression on audiovisual quality of these multimedia services and applications.

The effect of the source and display is particularly important and necessary for the case of 3DTV and high-dynamic range (HDR) displays, as both these technologies are not mature and still introduce quality problems. Display technologies are evolving from 2D to 3D, high-definition to ultra-high definition, low dynamic range to wide-gamut and high-dynamic range displays. In particular, HDR images are currently typically displayed on low-dynamic range (LDR) displays because of the limited availability of HDR displays. In order to visualize HDR images on LDR displays, tone mapping is necessary and this creates information loss that can deteriorate the quality and details of the HDR image. Recently, HDR displays have appeared on the market but they use internal processing that can affect the video quality. 3DTVs exhibit crosstalk to various degrees and can impact negatively the viewing experience. For these new technologies, the quality impact of the display and transmission (or camera, production and transmission) cannot always be separated. Although bandwidths available in cable transmission are well suited for ultra-high definition television (UHDTV), maintaining adequate video quality still represents a challenge. ITU‑R has recommended methods for the subjective assessment of picture quality (e.g. BT.500-13, BT.1788, BT.2021). There is a need to confirm that those subjective assessment methods and set-up requirements (including selection of the display, settings/calibration of the display, viewing distance, angle, luminance levels etc.) are equally applicable to the case of next-generation visual media, such as television transmission on digital or mixed analogue-digital chains, 3D, HDR and UHDTV images.

Concerning the measurement of the overall quality of experience (QoE), it includes not only a single impairment of each mono-media but also inter-media relation and response time of user operation. There is a need to identify the group of parameters that can provide objective measurement of the overall QoE and continuous in-service monitoring and control of it along the transmission chain.

In order to develop the two-way measurement techniques required for conversational applications, a basis in one-way audio and video quality evaluation must first be defined and validated. Considering the spread of broadband connections to business and the home, the bandwidths will support both low resolution, e.g. quarter video graphics array (QVGA), and standard, high and ultra-high definition imagery. As an example, audio multimedia applications currently range from audio for narrow-band applications, e.g. video telephony, to the enhanced audio contained in 7.1 surround sound systems for interactive gaming. In the future, HDR, 3D programmes and 3D games are expected to become more widely available. Objective and subjective methods for assessing the perceptual quality of these media services are needed, particularly those relating to transmission. These studies include the maintenance of and enhancements to existing Recommendations, and the development of new Recommendations as needed.

Much of the work on this Question (and its predecessors) was and will be done in cooperation with the video quality experts group (VQEG).

Study items to be considered include, but are not limited to: Tasks
Tasks include, but are not limited to: An up-to-date status of work under this Question is contained in the SG12 work programme 


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