Signal Processing: Image Communication 4 (1992) 263 264 263 Elsevier

Preface

All-digital high definition television" Dream or reality?

Had one asked this question a few years ago, the answer might have been quite different from the one today.

Rapid advances in video compression techniques and their implementation in VLSI have moved what seemed a cute but impractical idea towards a realistic solution to the problem of a new generation of television technology.

The professional arena has moved steadily towards fully digital solutions because of their obvious advantages in processing and storage of video. For consumer products, it was clear that digital solutions would gradually enter the picture, but initial costs would be too high unless high volumes (like those promised by an international standard) could be guaranteed. Also and until recently, the difficult problem of television broadcast did not seem amenable to a cost-effective high quality digital solution. However, over the last two years, several proponents for the new US HDTV standard proposed all-digital solutions for the terrestrial broadcast problem, and testing of such systems is currently under way. The standardiza- tion efforts for digital video by MPEG have also a definite influence in this context, since it will make digital video compression hardware affordable in the near future.

In Europe the situation is slightly confused due to the intended start of HD-MAC transmission via DBS in 1995 and the move towards a full digital solution in the US. However, two facts should be recalled. First, the HD-MAC system itself is fully digital as far as the receiver architecture is concerned and its complexity is much lower than the one of any hybrid coding scheme considered for this purpose. Only the transmission format is analog and suffers from the well known drawbacks. Second, the terrestrial broadcast infrastructures in the US and in Europe are very different and the taboo channels which are assigned for HDTV in the US are not available in Europe. Nevertheless it is commonly agreed that in a long term all HDTV-services will be digitized although the appearance of digital broadcast in Europe before the year 2005 is very unlikely.

On this background, several national and international (e.g. VADIS, RACE-DTTB) research activities concerning digital broadcast have been initiated and digital broadcast via satellite in the 20 GHz range will be demonstrated during the 1992 WARC conference in Spain.

In Japan, experimental satellite broadcasting of HDTV utilizing the MUSE system already started in 1989. Since November 1991, eight hours of daily broadcasting have been carried out. Digital HDTV broadcasting is considered as the second step after a new frequency band will be allocated at the WARC- 92. Meanwhile, various digital HDTV studio equipments are in operation for broadcast and production applications. Also, several types of HDTV coders have been developed and tested in field trials on actual satellite and optical fiber links. Aiming at the integration of television and workstations, the study of super high-definition images has started in several universities and laboratories. Full digital solutions are necessary for such super high-definition images.

Elsevier Science Publishers B.V.

264 Preface

Despite the current excitement, a number of technical questions remain to be solved, and the purpose of this special issue is to address some of them. Let us consider a few examples. Digital broadcasting is a relatively new idea, where both theoretical and practical questions have still to be solved. Because of the poor quality of the terrestrial channel, robustness to channel errors seems to be a key issue since high compression schemes are known to be very sensitive to errors. The integration of HDTV on workstations, which is one of the major benefits of going digital, raises questions since broadcasters and computer manufacturers have divergent opinions on what HDTV is or should be . . . . For compatibility and for transmission purposes, it is desirable to achieve a so-called 'digital hierarchy', but it remains to be seen what will be the best method to achieve it.

The 13 papers in this special issue are very timely in tackling some of the current issues in all-digital HDTV. The balanced representation from the three continents involved in the quest for the next generation television standard shows that, despite the competition and at least on a technical level, there is a fruitful exchange of ideas, and we hope this will ultimately lead to the best possible international standard for the future television system.

R. Sch/ifer M. Tanimoto

M. Vetterli Guest Editors

Signal Processing: Image Communication