AC055 TAPESTRIESList of participants
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The methods employed in TAPESTRIES are largely those of the psychologist, based around a number of carefully designed experiments. The results need to be skilfully interpreted in the light of statistical analyses. For example, Single Stimulus Continuous Quality Evaluation has been introduced into Rec. ITU-R BT.500. It is only after novel ideas have been experimented with and refined, that new methods for the assessment of application-specific multimedia will emerge.
Based on the analysis of psychological criteria related to specific applications of new entertainment media and display technologies, a framework will be developed for determining acceptability criteria. Methodologies will be developed for the subjective evaluation of a number of multimedia services against these criteria. This includes measures of 'presence' in immersive 3-D and virtual reality applications. Another important application area currently under study is that of distance learning. A new method has been formulated which involves subjects recording the correlation between audio and video using the SSCQE method. It is hoped by this means to develop a continuous measurement related to the ease of understanding of multimedia material in distance learning.
Visual modelling activities aimed at developing a perceptual distortion meter for MPEG-2 video include not only traditional theoretical studies based on the state-of -the-art, but also exploration of innovative and potentially more pragmatic approaches.
Summary of Trial
TAPESTRIES includes a subjective evaluation service to other ACTS projects and European broadcasters to determine the subjective quality and failure characteristics of a range of audio-visual services. During 1996, TAPESTRIES participated in a test carried out by CINENET to compare two systems for displaying high quality images: cinema projection and HDTV projection. The task asked of TAPESTRIES was the subjective test design, preparation and management, and the processing of the results.
TAPESTRIES also prepared, realised and processed the results of a QUOVADIS subjective test aimed at the analysis of the behaviour of the image quality of digital TV (DVB) under transmission error conditions on three different types of network: terrestrial, satellite and cable. In both cases, the tests were carried out using the SSCQE method.
Several further collaborations are planned with other ACTS projects during 1997.
Various application-specific uses of audio-visual communication are emerging within the broadcast and telecommunications industries. The key focus is now on ensuring that the service possibilities are developed to the same level as the transmission possibilities already have been, so that the environment will be set for growth in the commercial use of IBC networks. Asking the question "what level of quality will the viewer find acceptable for this application?" is of direct relevance to emerging multimedia applications. It is likely that the answers will vary between applications, and could well influence the economics and design of coding schemes. A correct understanding of the appropriate level of quality required, or "suitability for the purpose", is a key factor in determining appropriate usage of Integrated Broadband Communications networks. In the future, entertainment services are likely to be presented directly to the individual user in a manner which gives a more involving experience than looking at a simple picture display screen. A significant application area currently under study is that of distance education.
The virtual reality-type head-mounted display, the telepresence viewer or high definition multimedia screen, are all examples of ways in which entertainment and information will be imparted to the viewer. All these experiential immersive media will have psychological consequences for those who use them, both at work and at play.
These are matters of folklore today and urgently need to be understood and quantified. What causes the headaches experienced by the operator of a stereoscopic remote handling system? What health and safety guidelines are required for professional use of telepresence equipment? How do people behave when they are re-adjusting to the real world after prolonged immersion in a virtual environment? Just as regulators of television today are concerned about the disturbing effects upon viewers of subliminal suggestion or flashing images, what guidelines will they need for the future services?
One of the important requirements for images to be adequate for their purpose is perceived realism; that is, the degree to which a viewer accepts the image as a representation of a real world. This perceived realism will be related to image quality. The main dependent variables to be investigated are perceived realism and its relation to image quality, stereoscopic perception and its temporal course of development.
Meanwhile, the potential for multimedia applications brings an opportunity for the delivery of images which are adequate for their purpose, but are not necessarily of full-screen entertainment quality. This includes, for example, MPEG-4 proposals.
In summary, the key issues are:
Dr David Harrison Standards & Technology Independent Television Commission Kings Worthy Court Winchester SO23 7QA United Kingdom Tel: +44 19 6284 8646 Fax: +44 19 6288 6109 Email: (email removed)
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