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Content archived on 2024-04-19

Transcoding of Images for Terminals


New applications in the domain of television, conversational video services, and interactive information services will be realised through a set top box for the TV, and video telephony and other interactive services based on the PC or workstation. Many terminals will need to display video material from different sources at the same time. Such images may be in different formats, even incompatible to the display formats of the terminal (different aspect ratios, scan modes or field/frame rates). For video on PC and interactive TV, functionalities like resizing, clipping, slow motion are self-evident.

Image-format transcoding can overcome incompatibilities. This project will develop algorithms for high quality format conversions. Several hardware demonstrators will be constructed bridging the gap between TV and computers, and demonstrating transcoding functions in real time between different TV formats (Composite formats, CCIR 601, EDP, HDI, and HDP).
The main aim of the research was to investigate the need for video image transcoding resulting from the ever increasing number of image processing applications which have given rise to several new image formats with different aspect ratios (16:9 and 4:3), scan modes (interlaced and progressive) and field and frame rates (50Hz, 60Hz and greater then 60Hz for workstations). For multimedia applications there is also the need for displaying simultaneously one or more images or image sequences. Image format transcoding can eliminate these incompatibilities. In this research algorithms for high quality format conversions have been studied and the construction hardware demonstrators to bridge the gap between the television (TV) and the computer world on the one hand and to demonstrate the transcoding functions in real time between different TV formats, on the other have been investigated. Motion compensated schemes for high quality format conversions based on pixeel wise motion estimation have been elaluated.

In the area of composite decoding digital demodulation techniques and an adaptive digital comb filter have been developed. It has been demonstrated that these techniques lead to significant improvements in luminance chrominance separation resulting in elimination of cross colour and cross luminance artefacts.
The definition of key components for the cost effective hardware realization of image format transcoders has been completed.
Technical Approach

At a time when display resolution is increasing it is important to preserve image quality as much as possible during any transcoding process. Ideally, the quality of the transcoded image should be as good as is allowed by whichever of the original or the output display transmission format is the more limiting.

Candidate algorithms to achieve this quality target are studied by computer simulation, and later assessed on hardware demonstrators. Special-purpose integrated circuits are developed, to show that the selected algorithms could eventually be performed cost-effectively. The specific cases chosen for detailed study and implementation as hardware demonstrators will be limited to those for which a clear need can be foreseen and yet are not currently available at a sufficient standard of quality.

Key Issues

- Interfaces for motion video between the formats used by different video sources and displays.
- Simultaneous display of motion video from different sources on computer terminals (e.g. for multimedia workstations).
- Implementation of window functions for interlaced HDTV monitors.
- Special-purpose VLSI test chips for key transcoding functions.

Expected Impact

TRANSIT enables TV customers to obtain a cost-effective facility to display video originating from different image sources with different formats. For video on computers, transcoding between different image formats and the computer display format is a prerequisite for future multimedia terminals. The foreseen transcoding functions enable the user to simultaneously display motion video from different sources on the computer screen. For professional applications TRANSIT provides high quality interfaces between the various standards.


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Participants (10)