HDTV World Review Volume I Issue II: Standards Debates, European HDTV, and Industry Perspectives (Spring 1990)

Welcome to the HDTV World Review

The HDTV Review is only the second publication in the world, after the HDTV Newsletter, to be solely devoted to advanced television technologies and issues. It is a second tier of information for all those interested in HDTV, presenting the major positions of leaders in various areas. As Executive Editors, we are devoted to bringing our readers a compendium from the many millions of words spoken and written about ATV, and to keeping you informed about the issues. The Review is intended to further research, to assist the understanding of a changing landscape and to support decision making. We see the Review, like all our work, as a tool to help advanced television have a positive impact on business, industry, theater and the home.

The Review contains the reflections of key leaders—consultants, officials, executives, scientists, engineers, authors and others—which give you the structure and substance of the issues in an accessible format. It will help you to keep up-to-date with industry developments, and to decide how to plot an intelligent course through the communications labyrinth. We hope the Review will be a powerful library reference that is examined frequently to follow this new technology.

The Review is also intended to introduce HDTV to new faces. Whatever the final outcome of the movement toward advanced television, thousands—indeed millions—of people around the globe will be involved. Manufacturers and viewers in large numbers will play their parts in bringing about a new, powerful audiovisual communication with all the immediacy of television and film. As always, we solicit your comments and suggestions to help us better serve your needs.



Dale E. Cripps and Sam Bush
Executive Editors
From the Editor

In this, our second issue of the HDTV World Review, we continue our presentation of the major building blocks of advanced television. A valuable collection of articles has been gathered from people with vital interests and responsibilities in HDTV development. Herewith, a summary:

HDTV: How Many Lines?, by Gordon M. Drury
Gordon M. Drury’s remarks at the 1989 British Kinetoscope and Television Society (BKSTS) Convention offer an informed discussion of the practical realities of display, resolution and scanning structure, and a very sound background/tutorial for our readers. He moves right into an excellent presentation of the standard debates and the conversion issues, and closes with a look at common image and common data approaches to a world standard. This should be considered required reading.

The Role of Technology in the Future of Television, by William F. Schreiber
This vital and comprehensive review of HDTV conditions today is from MIT's advanced television research director. In many ways it is a parting shot, as this spring Schreiber retires from MIT after a distinguished teaching career of many years. His has been one of the leading voices in early ATV arguments. Schreiber presents a contrarian's view: simply improving picture and sound quality will not be enough to compel the public to buy, and additional services and benefits are required to make HDTV a hit. He is well-known for his advocacy of “open architecture” receivers, which by virtue of their on-board processors and smart circuitry could deliver any format to a standardized display. Here he looks at system design emphasizing transcoding requirements, practical transmission and spectrum conservation.

High Definition Television and the European Community, by Eamon Lalor
With the coming of the 1992 economic unification, the European Economic Community is taking ever stronger and more effective stands toward high-technology issues and industrial opportunities for its member countries. A broad range of communications technologies are in joint research and development by governments and private industry. HDTV is very much included through the Eureka 95 Project, headed by electronics giants Philips, Thomson and Nokia. In fact, in a short two years and with an investment of $200 million, the coordinated effort has brought to prototype hardware a complete 1250 line/50 field European system—the only true competition to the Japanese 1125/60—which was proudly demonstrated at the Berlin Funkausstellung in September, 1989. Lalor is the EEC’s senior spokesman on communications. His remarks here, from the HDTV Newsletter’s First International Conference (London, September, 1989) clearly delineate the very powerful and coordinated plan that has been developed for EEC members, both to benefit their industries and to block the Japanese. Lalor addresses why the directive came into place, and where it is going today.

The Ten Biggest HDTV Myths, by William G. Connolly
Distinguished engineer William Connolly (now president of Sony Advanced Systems) presents his HDTV myths, through which are reflected a Japanese manufacturer’s outlook. Key among these is the separation of HDTV production from transmission issues (in contrast to the European approach), with hopes of creating a market for today’s available production equipment—namely, 1125/60. In Connolly’s view, for the next 20 years HDTV will remain strictly a program and display medium, while computer power will stay in computers. He notes that Japan by no means dominates TV manufacturing in the U.S., and that the Eureka system is compatible with the European terrestrial systems. He bravely attacks the assertion that there needs to be a unique U.S. standard to protect American industry. He also argues that 1125/60 production has been successfully converted to both NTSC and PAL; that 1125/60 as a standard is not in fact strictly Japanese, but has had considerable input from other engineers, through the SMPTE in particular; and that viewers can clearly see the difference between HDTV and standard TV, contrary to some testing conclusions.

HDTV Studio Standards: Understanding the Debates, by Richard L. Nickelson
Nickelson is senior counsellor of the CCIR, the communications standards-setting forum of the International Telecommunciations Union (ITU). We are privileged to present this report on their work with international HDTV studio standards. Given the sensitive and economically important outcome of standards-setting and the CCIR's central role in it through its plenary meetings and extensive working parties, this article is an essential study of its processes. Specifically, Nickelson addresses study group 11's goal to develop a unique, worldwide HDTV production standard, taking into account existing emission and transmission systems and a variety of other factors. The enormity of the challenge is made clear here, along with the results of the extraordinary meeting and directions for future research. The paper was first presented at the HDTV Newsletter’s International Conference in 1989.

The Current State of High Definition Television, by Charles A. Poynton
Given the relationship that HDTV may or may not have to the emerging capabilities of the high-resolution computer workstation, one vitally interested party is the computer industry. Poynton, a Sun Microsystems engineer, has been stumping courageously in both camps for awareness and action through this period of HDTV parameter development, encouraging the most useful overlap of TV and computer technology. He suggests that we look closely at the potential interface details so that great opportunities will not be lost. Poynton believes that the computer users of this world should have access to the display screens and recording ease of the HDTV digital video world, a world of efficient speed density and playback which is foreign to computer users today. He also covers the square pixels argument, by which the difficulty of the four percent rectangular picture areas of video might be coordinated with computer descriptive language, so images and data can be exchanged without distortion. The square pixel matter has been central to the latest round of discussions—on the common image solution to an international production standard—by the standards advisory board, the Advanced Television Systems Committee (ATSC).

HDTV: An Historical Perspective, by Corey P. Carbonara
The second section of Carbonara's historical study further puts HDTV into the context of television's overall development. The period from 1940 to the present is divided into three stages, bringing us to today's conditions and unique new opportunities.

We are pleased to offer such diverse viewpoints. Our authors are highly regarded in their respective fields, and we hope their ideas will help you sort out the complex questions of HDTV. In upcoming issues, the HDTV World Review will carry articles on new HDTV applications and technologies. We invite your comments and submissions. We aim to provide the best possible HDTV coverage by bringing you in contact with the views of leading thinkers in this fast-changing field.

Editor

HDTV is a term which has become commonplace in broadcasting circles in recent years. It is a term which can, and does, mean all things to all people. Furthermore, television is concerned not only with the science of imagery but also with its art; in other words, the application of technology has to serve the program makers who create the images, as well as to provide the facilities to deliver them to the viewer. In view of the different aspects of a broadcast television service, each with its own peculiarities, there is opportunity for misunderstanding and confusion; the purpose of this paper is to review some of the technical issues with a view to dispelling some of this confusion.

It is worth recalling that, over 50 years ago, the monochrome 405-line system (CCIR System A), which has only recently been discontinued in the United Kingdom, was referred to as a "high definition" system. The CCIR System E, used in France and based on 819 lines, would, by this standard, have to be classified as an "even higher definition" system! Clearly, therefore, HDTV is a relative term and it is first necessary to be more precise if any discussion of it is to be meaningful.

What is HDTV?

Any system claiming to be high definition must be in some sense—but the question is, what sense?—better than what is already available. In the 1930s, the Schoenberg electronic 405-line system was comparable only to the "low resolution" 30-line Baird electro-mechanical one and, perhaps, the cinema. The Schoenberg system was described as high definition to distinguish it as being "better."

The experience of viewing television is a multi-faceted one but, for the HDTV debate, perhaps the most important features are that, in relation to the present systems, there should be:

1. Wider aspect ratio (16:9 rather than 4:3).
2. Larger and brighter displays.
3. Better resolution:


-Spatial.
-Temporal?
-Removal of scan artifacts.

A target would perhaps be to emulate 35mm film as the "cinema experience." The resolution issue is clearly a double issue because, to a large extent (although not entirely), the spatial and temporal aspects can be separated for clarity. The improvement of temporal resolution has been questioned in the list above only to highlight the fact that this is a parameter which causes most of the difficulties in achieving consensus on standards and may not be amenable to change.

The resolution argument requires that HDTV provide resolution which is better than 625 lines in 50 Hz regions and 525 lines in "60" Hz regions. It is relevant to place the 60 in quotation marks because the actual field rate for NTSC is 60 x 1000/1001, or 59.94 Hz; this is a material difference and has a bearing on compatibility issues.

It is also relevant largely to ignore the color coding issue since it is not material to the resolution discussion; whether the system to convey the multiplex of luminance and chrominance is NTSC, PAL, PAL-M, SECAM or MAC does not matter provided the respective resolutions of luminance and chrominance are balanced. It is clear, however, that there is a preference for basing a high definition system on separate component coding, as in CCIR Recommendation 601, rather than composite coding, in order to ease production processes and to avoid unnecessary quality losses due to cross-effects, etc.

Aspect Ratio

The viewing experience available with larger screens, with due note taken of the natural preferences of viewers for particular screen shapes, has led to the adoption of a greater aspect ratio than that currently used in television.

The film industry has used a number of aspect ratios for some considerable time (see for example British Standard BS 5550), and has taken note of the 4:3 ratio used in television when producing material specifically for that medium. Broadcasters have developed techniques for telecine machines to enable the showing of film in wider aspect ratios than 4:3; these include the well known "Letterbox" and "Pan/Scan." There is a clear consensus among broadcasters that an aspect ratio near 16:9 will be adequate; however, the problem of multiple aspect ratios for showing film will largely remain, and the existing 4:3 receiver will be used by the viewer for a long time yet.

There is hope that, as with new delivery schemes such as the MAC family, the ability to provide assistance information to an "intelligent" receiver will enable the viewer to be offered some greater choice of viewing format while retaining compatibility with existing or cheaper "unintelligent" receivers. The delivery of HDTV signals by means of HD-MAC takes this feature into account.

Displays

There has been for a number of years the hope that technology will be developed to provide for affordable displays capable of showing brighter and larger images than those currently used. The direct view cathode ray tube (DVCRT) has been, and seems likely to remain, the major technology for high volume consumer applications.

There are in existence techniques based on the projection of separate red, green and blue images from separate CRTs onto screens, but these are expensive and bulky and are not common in domestic use. Their quality and ease of use is not such as to cause a significant move away from DVCRT technology. Large DVCRTs (that is, more than 30-inch diagonals) are bulky, very heavy and need high EHT potential.

Brightness and resolution are mutually conflicting. Whereas the electron optics need to cover a large area of light-emitting surface with the scanning electron beam to produce bright light output, the achievement of high resolution images needs fine scanning beams which implies small area emission and reduced light output from the consequently small phosphor dots. DVCRTs seem likely to dominate the next decade of television and will therefore have a large impact on HDTV and its commercial development. Screen sizes in the home are unlikely to exceed those in current use; the main features affecting the development of displays are size and weight, rather than resolution, and larger images may only be possible at first on displays with relatively poor definition. It should be noted that our experience of HDTV so far is based on CRT displays and tubed cameras. New technologies such as liquid crystal display (LCD) and electro-luminescence show promise of escaping the problems of the DVCRT; but they do, of course, have their own characteristics which will lead to other defects or limits to performance.

There is, for example, the question of gamma for those new displays and whether, bearing in mind that DVCRTs will remain in use long after the introduction of new devices, gamma correction should remain in the camera rather than be moved to the device itself to allow freer receiver development. If the correction does move, it means that the video chain will need a greater dynamic range than presently since it will lose the advantage of 'companding' that gamma correction gave as a bonus. This means, in turn, that digital coding of television signals may need significantly more bits per sample (perhaps more than 50%) thus leading to significantly more bit rate in studios, especially videotape recorders (VTRs) and distribution links.

Resolution

The main improvement sought in HDTV is an increased spatial resolution— that is, more picture detail—and so the remainder of this article will be concerned with this feature. But first, temporal resolution will be discussed briefly.

Temporal Resolution (Motion Rendition)

Until now, no serious attempt has been made to improve the temporal resolution (that is, motion rendition) of television systems by increasing the picture frequency. The expectation that in the future new display devices will become available, and that they will be larger and offer more brightness, will call into question the use of low picture frequencies which lead to large area flicker at high brightness. This is likely if the new devices exhibit similar traits to DVCRTs.

The question of flicker at high brightness is not insoluble; the cinema industry has employed shuttering techniques successfully to control the flicker potentially arising in film where the picture frequency is only 24 Hz. Electronic shuttering in the form of 'up-conversion' has already been shown to be feasible in the receiver where the pictures are displayed at a closely related higher frequency than that transmitted.

This illustrates the distinction between flicker effects caused by artifacts of the equipment—in this case, the display device and its refresh rate (and to some extent, of course, the camera); and the flicker effects, better described as motion rendition failures, observed particularly with film judder or the well-known 'wagon wheel' effect. These latter defects are purely to do with temporal sampling and indicate that there really is a temporal deficiency in current systems of scanning. These defects are conveniently mitigated to some extent by camera integration and lag, especially at low light levels, but this situation is not likely to prevail indefinitely if charge coupled device (CCD) cameras come into more common use or if camera integration and lag are otherwise improved.

The radical improvement of these motion rendition effects in television, as well as film, can only be obtained by a significant increase in picture frequency; even 60 Hz television is not capable of sufficient improvement over 50 Hz in this respect. The advantage of 60 Hz over 50 Hz is confined to the display large area flicker artifact which, as already stated, is soluble by display processing in a receiver and so is not a major issue. The compatibility issue is the significant one and will dominate discussions on standards.

Spatial Resolution

It is noteworthy that, in both the historical schemes referred to in the introduction, the primary feature sought related very clearly to spatial resolution; more lines meant "better" pictures in that there should be more "definition." Definition and resolution are both terms which describe the degree to which pictures are perceived to be sharp and to provide the eye with fine detail. The clear consequence of this additional detail is, however, that more bandwidth is needed to convey the signal faithfully.

It seems self evident that more resolution can give more information but also that it can give the potential of more realistic and subjectively pleasing pictures. This is particularly the case if the pictures are to be viewed on larger, wider and brighter displays. The question is: How much resolution is needed? And, hence: How many lines?

It should be understood at this stage that the quality of sharpness in an image is a function of:
1. The original scene and the degree to which it contains high "spatial" frequencies, i.e., the source limit;
2. How much of this sharpness can be managed within the equipment available to process it, i.e., the practical limit; and
3. The fundamental limits set by the scanning system used as the basis of the system as a whole, including the degree to which the scan lines themselves are visible or cause visible artifacts such as interlace flicker.

The HDTV debate, while it seems to concentrate on the number of lines and field rate and so does not appear to consider the equipment or the scenes, is concerned with establishing that the fundamental limits to improved quality images are defined such that real advances can be made now and in the future.

It can be argued that, for all practical purposes, the current limits are not set by the fundamental parameters of the existing scanning standards but in the equipment, the scenes and the viewer's expectations and funds, and that there is ample room for further exploiting existing systems. This view has much merit, but so much of the infrastructure of broadcasting, particularly spectrum planning, has made long-standing assumptions about the spectral features of the images that their radical improvement would pose a serious challenge to this infrastructure and so it periodically requires some change. The simple example of the PAL system cross-color serves to show what happens when a system designed for the performance of cameras in the early 1960s is challenged by the resolving power of modern imaging devices.

There is no conflict in the view that HDTV systems should be pursued while existing scanning standards are still useful and are capable of further development. Choice for both the viewer and the producer of programs is maintained by ensuring that compatibility between new scanning standards and the still-developing established ones has the highest priority in the search for a new system. In other words, for broadcasters, evolution is preferable to revolution.

Image Scanning

It is naturally and widely assumed that HDTV will retain raster scanning and that the resolution target is double that available from current scanning standards. There will be a need to make due allowance for camera and display fly-back and so there will be an active picture area for each actual scan, whether it is interlaced or progressive (sequential), where the number of lines defining the resolution of the image provided by the optical system at the camera is less than the total number of lines in the complete scan period.

The use of interlaced or progressively scanned images is important to clarify. As early as the 1930s the work of Mertz and Gray as well as Kell and others indicated the limitations of raster scans and the technologies of the time (e.g., scan spot size) in resolving image detail. It was established, and can be demonstrated clearly today, that there was a worthwhile perceptible gain in the sharpness of an image scanned progressively compared to the same image scanned in an interlaced fashion, other things being equal. Modern repetitions of the early experiments have confirmed the effect; it is of value to retain the progressive scan option with a view to exploiting its benefits.

The relative needs of spatial and temporal resolution, balanced against limited delivery bandwidth, have traditionally been addressed by predominant use of interlace; the method is a balance between poor motion rendition (judder) with low picture rates (locked to the power distribution frequency in those early days) and better spatial definition obtainable with all lines in the same scan period. Interlace "flicker" is an artifact of this process caused by fine detail in the scene reacting with the reduced spatial resolution of each field of an interlaced pair and the spatial offset of one line between adjacent lines on successive scans. Progressive scan avoids this defect but demands doubled bandwidth for the same number of lines and picture rate. It is clear why the early systems chose interlace, but these limitations no longer present the same constraints and today's technology can solve most of the relevant problems. This is achieved by permitting the high bandwidth progressive scan to be used at the sources and displays where it can be managed, and to use digital signal processing techniques to "down-sample" the signal in a controlled manner to meet the constraints of the limited bandwidths available in the delivery and distribution media. Receiver processing can be used to restore the image quality and to overcome the defects of the display, as described above.

The key to this possibility is the realization that the raster scan samples the image in the vertical direction and is subject to the constraints of Nyquist's criterion. Whereas, however, the normal technique is to filter the signal prior to sampling to ensure that no frequencies above the Nyquist limit are present, there are no formal filters in the optical system of the camera or telecine. There is complete reliance on the natural limits of the lens' optical resolution to limit the detail of the scene reaching the imaging device. In practice this is not sufficient because the MTF of optical systems generally degrades gracefully and so is not rapid enough to avoid aliasing at the scanning stage and it is thus present in any subsequent signal. With tubed cameras (and to some extent with tubed telecines) there is at least the prospect of using the scanning aperture of the spot, together with the corresponding aperture correction, to adjust the effect by using light averaging over a large spot area whose shape can be used to some small extent to balance horizontal and vertical resolution.

With CCD arrays this is not so easy because the cell sizes are fixed and their aspect ratios must allow for all the practical factors involved such as maximizing elemental area for sensitivity, minimizing the same for resolving power, and permitting all the connections to the cells to be accommodated on the array. In addition, the number of cells in the array's columns and rows have to be chosen to oversample by a sufficient margin to avoid the worst effects of direct scan aliasing; this margin can be significant and increases effective sampling density considerably. Processing beyond the imaging device could be used to interpolate to a lower sampling density and thus filter the signal to the desired degree.

There is an assumption that HDTV will be specified in a digital format where the effective sampling in the temporal and vertical directions will be augmented by sampling in the horizontal direction. This does not mean that HDTV is exempt from any constraints or that its properties are more easily described in the digital domain. Equation 1 relates the (horizontal) sampling frequency, Fs, to the other primary parameters of any television scanning system using a raster scan:

1. Fs = S. L. Ff
Where S = samples per line, L = lines per picture, and Ff= pictures per second.

This equation can be refined to take account of the active and blanked periods in the lines and pictures:
2. Fs = (Sa + Sb). (La + Lb). Ff = Br/N
Where Sa = Samples per active line, Sb = blanked samples per line, La = active lines per picture, Lb = blanked lines per picture, Br = bit rate, and N = bits per sample.

It is the aspiration of the standards studies on HDTV to arrive at a single set of parameters which will be satisfactory for the future and will provide compatibility with existing systems.

Sampling Structures

Equation 2 above contains all the important parameters which need to be defined and can be used to explore the relationships between various candidates for standards. However, the equation does not reflect the sampling structures to be assumed; the equation will apply equally either to interlaced or progressively scanned pictures. The image is transformed into a sequence of samples and, to some extent, this disrupts image structure. The sequence does not have to be exactly related to the sequence of the natural scan. It is important to understand the role of sampling structure for it underlies the possible "family" aspect of the HDTV standard and its compatibility and future development.

The case of the interlaced and progressive scan comparison is an example of a more general case where the locations of potential sampling points on a rectilinear grid define the performance of a system. If the two scans are compared by illustrating the arrangement of lines in the vertical/temporal plane, it can be seen that consecutive scans use information about the image which is taken from two different locations in the grid. The arrangement of the repeating cell of five sample points arising out of this scheme is called "quincunx" (see figure).

If this same quincunx arrangement is applied in the horizontal/vertical plane, for the moment retaining progressive scan for the example, then it is possible to form a different interlaced sequence of samples which has the same sample rate as conventional interlace. Instead of completely suppressing alternate lines of the progressive scan to produce conventional interlace, the quincunx pattern suppresses alternate samples along each line of the same scan. For an odd number of lines in a total picture, conventional interlace repeats every two scans. The new quincunx pattern also repeats in two scans; the samples which were omitted in the first scan (black points) are taken in the second (white points), thus enabling the scheme to carry all the resolution that interlace can but with reduced interlace flicker due to the presence of samples from each line in each scan. Whereas conventional interlace has defects due to fine vertical detail the new scheme will have flicker only in the presence of fine diagonal detail, which may be less disturbing to the viewer and a rarer event in real images. Furthermore, the eye may tolerate a modicum of diagonal filtering to suppress such alias as does occur. The new quincunx arrangement is otherwise known as "spot wobble" and is familiar from the early days of television.

Other arrangements of the sample patterns in the grid can be made assuming either progressive or interlace scans as a starting point. The main value of examining these patterns is that they identify the way in which samples can be suppressed under controlled conditions such that the sample rate can be reduced, thus reducing the demand on transmission or storage bandwidth. Quality can be preserved if sample suppression of this kind is chosen carefully and is reversible so that it can be performed at the receiver to restore the full image resolution quallty. Such processes are the basis of the HD-MAC system. The close connection of the production scanning standard to those sample patterns which are amenable to reversible manipulation for the purposes of bandwidth saving (for recording or transmission) is vitally important for successful standards design and compatibility.

The Standards Forum

One of the candidates is the European 1250/50 system; another is the Japanese 1125/60 system. Both these systems are proposed as single world standards but the compatibility between them is small. Whereas the 1250/50 proposal is based initially on compatibility with the European 625/50 environment, a similar approach does not seem evident with the 1125/60 proposal, where compatibility with the 525/59.94 environment might have been expected.

For many years the standards conversion process has been used to convert program material between the two existing standards. One of the aims of a single standard for HDTV is to remove this need; if this cannot be achieved then at least the agreed standards should minimize the difficulties and maximize the compatibility with existing production and delivery arrangements. Among these is the growing use of CCIR Recommendation 601 as a basis for forward-looking systems, e.g., MAC; compatibility with it is a major aim since it is a dual standard having good relationships with both 525 and 625-1ine systems. The reasons for this are summarized in the following equations:

F(525) = 525.60/2. 1000/1001 = 15.734. . .KHz
F(625) = 625. 50/2 = 15.625 KHz
Ratio: F(525)/F(625) = 1. 006 993. . . = 144/143
That is: 144. F(625) = 143. F(525) = 2.25 MHz

The frequency 2.25 MHz is an important parameter in maintaining compatibility between any new proposal and Recommendation 601.

The maintenance of common sampling frequencies for the 50 and 59.94 Hz versions means that, for HDTV, a common sampling frequency which is also a multiple of 2.25 MHz is necessary. One analysis of Equation 2 suggests that only one set of parameters leads to common sampling frequencies and the set includes 1250/50 and 1050/59.94 for the number of lines at each of the two field frequencies. Furthermore, the sampling frequency for conversion to digital format is common at 72 MHz; Equation 2, linking the important parameters quoted above, yields the following:

50 Hz 59.94 Hz

Lt 1250 1050
Sa 1920 1920
Sb 384 368
La 1152 968*
Lb 98 82
Fs 72 MHz 72 MHz
Br 1152 MBit/s** 1152 MBit/s **

where Lt = total number of lines per picture.
* The 59.94 Hz specification in Recommendation 601 does not define a value for La but Recommendation 656 quotes 507 lines.
** Eight bits per sample is assumed.

The approach exemplified in the above table propagates the philosophy of Recommendation 601 and leads to a common gross data rate at about 1150 MBit/s which is a common basis for the design of videotape recorders and transmission equipment. The consequence is that the differences in balance between spatial and temporal resolution, originally defined when the 525 and 625 systems were agreed, are retained in the HDTV standard and leave the image quality unequal between the two parts of the dual standard.

There is another view which seeks to move away from the philosophy of Recommendation 601 sufficiently far to remove this distinction and to have an equal image quality in the sense that there is an equal number of samples per active image, with the samples arranged in an identical way in each case. This is known as the common image format: the corollary is that there should be equal horizontal and vertical resolutlon so that all picture elements are "square." The horizontal active picture width will consist of 1920 samples; for a 16:9 aspect ratio and "square" picture elements there should be 1080 active lines in the scan. Horizontal and vertical "Kell" factor will not be precisely the same in practice, so that a square picture element is not necessarily a major issue. The number of lines in the active scan does not have to be precisely 1080; in fact, due to the different 'Kell' factors, there should be relatively more sample points vertically (i.e., lines) to equalize resolution.

The consequence of the common image format is that the gross bit rate (see Equation 2) is directly related to picture frequency and so will differ greatly between the regions using 50 Hz and 59.94 Hz unless the use of the blanking parameters offers enough flexibility to recover the discrepancy. In order to do this and retain a multiple of 2.25 MHz for the sample frequency it may just be feasible to reduce the blanking periods in the 59.94 Hz signal and increase those in the 50 Hz signal so that the common image format proposal can allow a precise compensation for the field rate differences and thus lead to a common data rate. A tentative view is that this is just feasible but would only be useful for instances where the gross bit rate (i.e., inclusive of blanking) is important; in most processing applications and in recording and in bit rate reduction codes, blanking is discarded, leaving the common image format approach with the original bit rate discrepancy. Furthermore, compatibility with existing scan formats and blanking proportions is affected.

Causing the gross bit rate to be so disparate creates significant difficulties for the design and construction of videotape recorders and for transmission related equipment, where bandwidth is a crucial parameter. It could be possible in the case of the VTR to have an equivalent track layout to the image format so that track layout and image sample structure have a close correspondence. This would direct all differences of design towards linear tape speed, so that higher picture frequency would mean higher tape consumption. It would still require the circuits of the VTR to handle higher bit rates for higher picture rates and additional heads, accessing additional tape area when in high picture rate mode, may be needed on the scanner. Another approach is to use the same mapping of image-to-tape but to use an increased head-to-tape speed to deal with the increased bit rate.

The agreement on identical image parameters (see Equation 2) would restrict the problem areas to one parameter—picture frequency—and the differences between the requirements of 50 Hz and 59.94 Hz users would be dealt with, it is claimed, by means of relatively simple picture rate converters using motion compensation techniques.

The CCIR, at the final meetings of the current study period, hopes to choose a single world standard for HDTV; if this proves impossible it may consider an alternative approach based on one or both of the above two proposals, perhaps combined in some form of compromise. In view of the vast investment in communications and broadcasting infrastructure in each of the 50 Hz and 59.94 Hz regions, it seems unlikely that a common standard will be agreed on either of these frequencies: the advantage to the successful system would be too significant. A search through the array of possible number sets arising from Equation 2 in the region of 1000-1200 lines raises few hopes for compromise. The difficult case of the 1125/60 system will have to be included in the search in order to achieve full agreement on this compromise and may require an adjustment to be made by all parties.

It seems more likely that there will be a dual standard: the choice between the rival proposals is not easy, but the existence of the agreed Recommendation 601 must lend support to the common data rate proposal. On the other hand, the achievement of equal image quality for both 50 Hz and 60 Hz systems would be a useful advance. The isolation and emphasis of the picture rate as the only underlying fundamental difference between systems across the world, which is inherent in the common image format proposal, concentrates the standards conversion problem on a single parameter which happens to be the most difficult one to deal with. The common image format approach seems to polarize the world standards situation and the only resolution of the dilemma seems to be the practical, free-market opportunity which may lead to one picture rate becoming dominant over the other. There are clearly many obstacles to such a possibility.

Gordon M. Drury began his career in research and development, working on the high-speed digital transmission of broadband telecommunications signals, including television. In 1972 he joined British Telecom and became involved with satellite systems, with particular responsibility for the development of digital systems such as TDMA. In 1974 he joined IBA’s experiment and development department, to work on network transmission of digital TV. In 1977 he became project leader of the digital videotape recorder work. During this period, he also worked with EBU study groups, especially those connected with digital studio standards for television. In 1981, Mr. Drury began work on the study of the implementation of the 4.2.2 standard. One outcome of this was the MAC system for DBS, with which he had some close connection; he also had a specific role in evaluating analog components formats for transmission links and for video recording. He has published papers on transmission and recording in industry journals and at IBC. In 1986, he was appointed to the Satellite Engineering Department to assist the implementation of U.K. DBS based on DMAC. In 1988 he was chosen to head of the baseband group in the experiment and development department. This group is working on projects involving MAC systems evolution, HDTV, image processing, digital TV transmission and coding for still and moving images, data broadcasting, digital audio, specialist software and studies on terrestrial system development.

Summary

Simply improving picture and sound quality is unlikely to provide the public with sufficient incentive to buy HDTV receivers in large quantity. Even that improvement is likely to be difficult to achieve, particularly in terrestrial channels, unless means are found to overcome analog channel impairments. Actually, viewer behavior indicates that greater program choice is much more desirable than resolution enhancement. International and domestic controversy over standards, and over whether a new system should be compatible with the installed base of receivers, is primarily economic in nature. There is also widespread need to improve the efficiency with which TV utilizes spectrum so that important new services can be accommodated.

In view of this, it appears that technology has several potentially more fruitful roles in HDTV than merely increasing the resolution of studio pictures. One is developing transmission systems that can deliver the improved quality to the home under practical conditions. Another is facilitating transcoding among the various formats that will be used in different media and different countries and at different stages of an introduction scenario. Another is providing more viewable channels of a given quality with a smaller overall allocation of spectrum, thus making spectrum available for alternative uses.

An approach to system design that can support all these requirements is described in this article. It is based on adaptive subband coding and scrambling. The achievement of superior performance depends on the eventual abandonment of NTSC and similar formats, which are inherently wasteful of bandwidth and highly vulnerable to channel defects. Simulcasting is required during the transition period to a new system. It is believed that this is not only practical, but that it is more likely to end up with a satisfactory system than approaches based on receiver compatibility.

Here, brief descriptions will be given of the various techniques mentioned, together with some numerical examples illustrating the benefits that can be obtained by using this approach to TV system design.

Introduction

The character of current discussions in the CCIR and the United States about HDTV production and transmission standards shows that economic and political considerations dominate thinking on this subject. Since television, above all, is a business involving profit and loss both to companies and to countries, this is to be expected, and, perhaps, appropriate. However, the success of any new television system depends, ultimately, on the willingness of viewers to pay for receivers and for the service itself. If viewers have a choice, they will not accept a new service unless it offers obvious benefits. The evidence is, at least in the United States, that the benefit most desired is a larger number of attractive programs rather than the higher spatial resolution that might result from strictly technology improvements. This is true in spite of the fact that picture quality in typical American homes is extremely poor.

In Europe and Japan, direct broadcasting from satellites (DBS) is the delivery mechanism to be used initially for HDTV. In both regions, the number of broadcast channels now available to viewers is much smaller than in the U.S. Therefore, the primary attraction of the new service is likely to be the additional channels provided, rather than the higher definition due to the HDTV scheme or the freedom provided by DBS from terrestrial-transmission defects such as noise and ghosts. If viewers have the option of using their existing receivers in the new service, the rate of penetration of high-definition receivers is likely to be very low. A relevant prior example is the very slow acceptance of color receivers following the introduction of compatible color in the U.S. in 1953. This occurred in spite of the fact that the addition of color was a spectacular improvement clearly evident to the most uncritical viewer. Higher definition provides a much smaller quality increment than adding color.

There are much clearer roles for technology than simply increasing resolution. These include overcoming transmission impairments so that terrestrial channels can be used successfully for HDTV, improving the efficiency of channel utilization, and dealing with the transcoding problems that arise due to differing national standards and to the necessity of optimizing performance in different transmission media.

The basic cause of the vulnerability of NTSC, PAL, and SECAM to terrestrial channel impairments, as well as the cause of their inefficiency in the use of channel capacity, is the highly nonuniform spectrum of raster-scanned video signals. By the use of a combination of modern techniques including subband coding, adaptive modulation, and scrambling, the transmitted signal can be made to have the character of white noise. In that case, excellent picture quality can be obtained in a single six MHz channel in the presence of very high levels of additive random noise, interference, and multipath conditions. Encryption is inherent. The improved interference performance permits many more channels to be provided within a given overall channel allocation. This is particularly important in the United States where there is great pressure for releasing some channel capacity now allocated to television for other purposes, such as cellular telephone service.

The distribution of energy in the subbands depends on motion, and thus varies a great deal across the image and with time. Adaptive selection of subband components on a block-by-block basis within the image is therefore feasible. This is equivalent to adjustment of the spatiotemporal frequency response in accordance with local image characteristics. The procedure, which does not require the use of explicit motion compensation, produces a very large improvement in the sharpness of both still and moving objects, since channel capacity can be devoted to just those components having significant energy at each point in the image.

There also appears to be a technological solution to, or at least some amelioration of, the vexing problem of transcoding. Sequential transmission of subband components in blocks of nominal length 1/12 second allows transcoding between the transmission formats and both the display and production formats at all common frame rates using integral temporal interpolation/ decimation factors. Transcoding between various transmission formats that have been optimized for specific transmission media (terrestrial, cable, DBS, fiber, etc.) can be done easily using neither spatial nor temporal interpolation.

Political and Economic Considerations

Who wants HDTV? There is no grass-roots demand for higher resolution or wider screens. While viewers do occasionally complain about specific problems, the overwhelming desire of the mass audience, as revealed by its willingness to rent videocassettes and to subscribe to cable stations, is for more and better programs. On the other hand, few viewers are willing to buy proper antennas. HDTV is primarily pushed by the technology itself and by the desire for profits and market share. There is nothing sinister about this; the audience didn't know beforehand that it wanted VCRs or digital audio either.1 A more important question is how the benefits of HDTV, which will be primarily economic, can be maximized and provided to all concerned.

Many believe, as a matter of principle, that such questions ought to be left entirely to the market. However, a truly free market cannot exist for TV systems. Governments must decide questions of transmission standards and spectrum allocation. Decisions on these matters affect not only broadcasters, manufacturers, and viewers, but have very large effects on other industries and on international competitiveness. The recognition of these effects in the U.S. has raised the HDTV issue to one of transcendent national importance.

Economic significance of the consumer electronics industry. In the U.S., this industry is $40 billion annually at retail, and growing. It is almost entirely foreign-owned, although some value is added to receivers assembled in the U.S. in foreign-owned factories. The only significant American manufacturer of receivers is Zenith, whose assembly operations are largely located in Mexico. A report commissioned by the Department of Commerce predicts that HDTV may well account for $140 billion in the first 12 years, representing hundreds of thousands of jobs. The manner in which the domestic consumer electronics industry decayed, which involved massive illegal dumping by Japanese companies and which also destroyed the commercial electronic components industry, is having an important effect on American views about dealing with the advent of HDTV.

Consumer electronics is a fiercely competitive industry with rapid innovation and very short time to market. It thus drives the entire electronics industry technologically, including industrial and military electronics. Video technology is already important to computers, and some believe that the pervasiveness of digital signal processing in HDTV receivers will ultimately drive the design of computer digital hardware as well. HDTV is expected to use large numbers of semiconductor chips, including memory and microprocessors, and thus have an important effect on the semiconductor industry. These indirect effects may well be larger than the direct effects. In view of the overwhelming importance of electronics and computers to industry generally, it is probable that HDTV will have a pivotal role in determining the competitiveness of industry as a whole.

HDTV as a trade issue. No country can afford to be insensitive to its balance of trade. Trade imbalances must be compensated by loans, sales of assets, and gifts. Ultimately, the standard of living depends on the net flows of money, services, and goods across national boundaries. A high standard of living absolutely requires a vigorous domestic manufacturing sector; we cannot live well by services or agriculture alone. This being the case, and in view of the expected economic impact of HDTV, the prospect of its introduction entirely under foreign control is deeply troubling. These were the primary considerations behind the European decision to develop its own system through the Eureka program. Similar views underly current American discussions on this issue.

Standards Considerations

We have recently seen a contentious international debate over production and program-exchange standards. From the technological point of view, this debate has been conducted on a faulty basis, as production and exchange standards have very different requirements. More careful consideration shows that there are a number of different classes of standards to be worked out, and they have different requirements and different needs for international agreement.

There are four kinds of standards! In the figure, a conceptual diagram illustrates a complete TV system, from the scene in front of the camera to the final display in the home. Except for the labelling, the scheme shown is not markedly different from that now used. At present, NTSC2 is used throughout the system, although some variation in format is sometimes found in satellite transmission or in tape recording. In future systems, however, different signal formats (standards) will be used in different parts of the various complex paths traversed by video information from the original camera to the display in the home receiver. This will be done because it is now well known that it is advantageous and because the components are available to make it feasible.

1. Production standard. The primary requirement is suitability for postproduction, the program-assembly operation used to combine different elements from various sources (not necessarily in the same format) into a single entity, usually on videotape but sometimes on film. The spatial and temporal resolution must be high enough for the most demanding intended use, but not excessively high as this causes loss of camera sensitivity. A progressively scanned (no interlace) normal video signal, analog or digital, is best. Standardization of this format is simply a convenience for manufacturers and program producers and need not be the subject of government-to-government agreement.

2. International program-exchange standard. The primary requirements are adequate quality and easy transcoding into the transmission formats that are to be used in the various countries (50, 59.94, and 60 fps) and secondarily to 24-fps film. Bandwidth efficiency is desirable but not mandatory. This is the one standard that most requires agreement for the purpose of facilitating international trade in programs.

3. Transmission standard. This is technically the most difficult, as it requires maximum picture and sound quality for a given bandwidth, and good performance in the presence of normal channel impairments. The exchange and transmission formats need not be conventional raster-scanned, ready-to-display video signals. NTSC, for example, is a very inefficient format. Good interference performance is required for optimum spectrum allocation, and encryption is needed in some applications. Since the various channels—over-the-air, cable, satellite (DBS), VCR, and digital fiber—all have different physical characteristics, a single transmission standard is impossible if it is desired to optimize the performance in different channels. Easy defect-free transcoding between the various transmission formats and a range of receiver display formats is essential. Easy transcoding into today's standards (NTSC, PAL, SECAM) will be important at least for the next ten to 20 years. International agreement is helpful, but not essential.

4. Display standard. As high a line and frame rate as affordable should be used at the display so as to achieve the highest possible quality for whatever information is transmitted. Conventional raster-scanned video is appropriate. Easy transcoding in receivers between the transmission and display formats is essential. Because of the very large volumes involved, it is feasible to develop special very-large-scale integrated circuits (VLSI) for this purpose, both application-specific (ASIC) and programmable digital signal processing (DSP) chips. Of course, HDTV receivers all will have frame memories. Standardization of the display format is highly undesirable, as it unnecessarily limits the manufacturer in producing a full line of products for different applications at different prices.

Control of markets through standardization. Countries have often attempted to control their markets by standardization, backed by patent protection of the system adopted. This was the principal reason why Europe selected PAL in 1965, and why France adopted SECAM. Many believe it is also the main reason for the attempt to have the NHK 1125-line system adopted as an international standard for program production and interchange. In this context, the adoption of the European HDTV system developed under Eureka may be seen as a defense against Japanese domination of this next stage in the development of television all over the world.

In addition to patent protection, an important element in relative commercial advantage is the learning curve. Companies and countries that are first in a new technology, such as a new television system, normally can maintain their lead for some time, even with open competition, simply because of experience gained during research, development, and early production. In the case of electronic systems, setting up factories, tooling, and development of complex integrated circuits all take time and cost money. The first in the field therefore has a cost advantage which may be extremely difficult to overcome. Thus, even if the European system were no better than the Japanese system, its adoption would be to the advantage of European manufacturers.

Effect of standards on the growth of HDTV. The rapid proliferation of a new TV system requires timely investment by manufacturers, broadcasters, and viewers, all of whose action will be influenced by cost/benefit expectations. No one will invest in equipment expected to be soon made obsolete by changes in standards. This is the reason why many groups are demanding early agreement on a single standard. On the other hand, especially in view of the rapid technological progress being made by many groups and the lack of extensive operating experience with any HDTV system, an early decision may well be far from optimum. For example, it appears that transmission degradation, and not the numbers of scan lines or bandwidth, sets the practical limit to picture quality in the home in the case of terrestrial broadcasting. Should the actual quality of the chosen standard be disappointing, HDTV may well be a failure.

Some standards situations may be disastrous. One that should be avoided if at all possible is the development of a number of mutually incompatible de facto standards. This might happen if HDTV were first introduced in niche markets, such as DBS or cable narrowcasting. When it became apparent that receivers bought for one system could not be used for another, massive viewer disenchantment would be inevitable. If this happened in the U.S., legislative correction could be expected, a most unlikely route to a satisfactory standard. Even if a single de facto standard prevailed, since it would have been developed for one particular purpose, it might well inflict high cost and low quality on other applications. Such considerations point out the desirability of a national or international standard-setting procedure that would take account of all pertinent needs.

One transmission standard or many? At the present time, live TV signals are delivered to the home primarily by over-the-air (terrestrial) transmission and cable. DBS service has started, and optical fiber is expected to become a significant factor in the future. VCRs are also very popular for recorded material. NTSC, or a minor modification of NTSC, is used for all these channels,3 thus simplifying the exchange of signals.

The different channels have different channel capacity and other characteristics. It is possible to optimize transmission formats taking this into account, so that the highest quality can be obtained in each case. Depending on the difficulty of transcoding from one to the other, different formats may inhibit the easy interchange of signals that is essential to an effective distribution system. Forcing a single standard on all the media, however, will limit the quality of all to what can be obtained with the poorest, which is generally the terrestrial channel. This clearly accounts for the fact that the terrestrial broadcasters are calling for a single standard, while the voices of the other media propose that each be allowed to develop to its maximum capability, transcoding aside. This also points up the desirability of systems that permit optimization while also facilitating transcoding.

Compatibility with Existing Systems

Nothing excites controversy as much as the question of whether new systems should be compatible with today's receivers. As the installed base approached 500 million worldwide, compatibility seems to be obviously desirable. The question is not as simple as it seems, however. When one considers the introduction scenarios, the overall economic effect, the useful life of receivers and professional TV equipment, and the likely state of the entire telecommunications industry after the transition takes place, the case for compatibility becomes much less strong. Some guidance may be had from analyzing the compatible introduction of color in the U.S. in 1953 and the noncompatible introduction of color in France and the U.K. in 1965.4

In the first case, to protect the existing 10 million receivers, a system with serious defects was adopted; the new system, although ultimately successful, grew very slowly. Without the determination (and deep pockets) of David Sarnoff, it is not clear what the outcome would have been. What is clear is that if viewers, whose overwhelming concern is the program and not its technical quality, can watch new programs on old receivers, their incentive to buy new receivers is greatly diminished.

In the second case, a transition to an entirely new system that offered uniformity across most of Europe was successfully carried out. This also required money and determination, but it led to a much more desirable result.

Evolution or revolution? Outside the television field, compatibility appears to be the exception rather than the rule. AM/FM, analog/digital, horse carriages/automobiles, 8mm movies/ VCRs, are all examples where one technology replaced (or is replacing) another without complete compatibility. The real and perceived advantages of the new product or technology were sufficient so that the old was discarded in favor of the new. Not even the best constructed product lasts forever. In most cases, the two lived side by side for some time. One suspects that many households switched to the new at normal replacement time.

In Japan, HDTV is being introduced via DBS as a new service in addition to, and not as a replacement for, NTSC, which is to remain as the terrestrial service. New receivers will cope with both. Under these conditions, the technical format of HDTV need not bear any relationship to NTSC. In fact, the intention is to be as different as possible and to use different programming that is deliberately produced so as to take advantage of the capabilities of the new system. It is a revolution, but one that is not intended to replace the present system. Whether the independent NTSC terrestrial broadcasters will be content to become the "AM" of television, while NHK's DBS HDTV becomes the "FM," remains to be seen.

An evolutionary approach requires both that there be a clear technological sequence from the old to the new and that the audience be willing to make timely investments for the sake of necessarily smaller increments in picture quality. The latter will be encouraged in Europe by the newly available channels, but there will be no such incentive in the U.S. This certainly means that market penetration of HDTV receivers will be slow, and the required economies of scale correspondingly slow in coming. That situation will surely test the staying power of both broadcasters and manufacturers.

Technological limitations of compatible systems. Perhaps the most important obstacle to the compatible approach is technical. There is no question but that the requirement to be compatible with today's receivers must place an enormous restriction on the design of a new system. Barring some new invention, this will reduce both the bandwidth efficiency and the resistance to channel impairments that can be attained. For example, the NHK nine MHz compatible system has somewhat lower quality than the six MHz Narrow MUSE. MIT's proposed nine MHz compatible system has slightly lower quality that its six MHz noncompatible system.

The extremely poor interface performance of NTSC, which leads to high required CNR for satisfactory operation and also makes for highly inefficient channel usage (less than one third of channels can be used in any one location) is inherent in the NTSC signal design. Compatible systems surely will not be better in this respect; they may well be worse. We now know how to solve this problem, but it requires a totally new system. Compatible systems must have lower technological performance. Systems that are permanently compatible must have lower performance forever.

Some Important Technological Problems

While the experts often bemoan cross-color and cross-luminance and sometimes interlace defects, NTSC studio pictures are actually quite good. They are so much better than the pictures seen in typical American homes that today's audience would be delighted to get them. HDTV images, if degraded as NTSC now usually is, will have little market appeal. NTSC's extreme vulnerability to interference leads both to low quality and inefficient utilization of spectrum. The latter is particularly serious given the competition for spectrum from land-mobile radio. Finally, interlaced composite systems such as NTSC make for expensive and less-than-perfect transcoding, especially between disparate frame rates.

Transmission impairments. Reception in American homes is degraded by noise, ghosts due to multipath transmission, interference, and imperfect channel frequency response. The simple amplitude-modulation system of NTSC has no protection at all against such defects, which constitute the principal limitation to picture quality. They must be dealt with in order to deliver HDTV's higher-quality images under practical conditions.

Interference performance. Although this is a transmission problem, it is not only due to the use of amplitude modulation. Excessive amplitude of synch pulses is to blame, but the trouble is mainly due to the highly nonuniform spectrum of all raster-scanned video signals. The higher-frequency components are actually transmitted at very low power, and are therefore easily corrupted. At the same time, the low-frequency components and picture carrier are at very high power, and therefore interfere a great deal with other signals, whether in the same or adjacent channels. Thus, adjacent channels cannot be used in the same city, and stations on the same channel must be about 200 miles apart. As a result, even though nearly 70 channels are allocated to TV and cannot be used for anything else, only about 20 are actually available at any one location.

Spectrum efficiency. In the past, we have thought about this in terms of the quality that could be achieved within a certain channel capacity, i.e., the CNR and bandwidth for analog channels and the data and error rates for digital channels. Good performance requires a visually efficient image description (source coding) and an appropriate modulation method for the particular channel (channel coding). A broader view is provided by thinking about the number of channels and the quality provided at each receiving location as a function of the total spectrum allocated for television. The spectrum that could be made available by shifting to a bandwidth-efficient system would provide, for example, the opportunity to develop a highly desirable mobile telephone service. From this point of view, the interference performance, which regulates the minimum station separation in both space and frequency, is just as important as the picture quality that can be obtained in one channel. In both respects, NTSC falls far below the level of performance possible with modern methods.

Transcoding. Today's bewildering array of formats will not automatially disappear with the advent of HDTV; it is likely to get worse. The protectionist sentiments that motivated the present split are still present, and the need to adapt the format to the specific characteristics of the various media, now including digital channels, is strong. Given the enormous investment in today's equipment, and the consequent need to transcode HDTV formats into existing standards for many years to come, the cost and quality of transcoding must be carefully considered in any new system proposals. Note that the critical transcoding point is between the international HDTV exchange format and the transmission formats used in the various countries and various media. Since these transcoders will never be made in large quantities, we cannot rely on mass production to make them cheap. We must, instead, choose a system design that inherently provides inexpensive transcoding at this point in the distribution system.

Fundamental Weaknesses of Current Broadcasting Formats

Important lessons can be learned from examining why TV now uses such an enormous amount of spectrum and, at the same time, is so vulnerable to interference and other channel impairments. As in any other communications problem, source coding and channel coding are the tools at the hands of the system designer. Due to a combination of mostly historical circumstances, among which the need to have very simple receivers was probably the most important, we are now using a remarkably inefficient system. The opportunity to correct such a situation comes no more than once in 40 or 50 years. With the pending choice of an HDTV system, such an opportunity is now at hand. We can select an entirely new system that will give much better service to the viewer and, at the same time, use much less spectrum, or we can stay with what we have and suffer poor quality and spectrum scarcity for decades to come. One can only hope that those involved will be wise enough to make a good decision.

Redundancy. It is hardly novel to point out that traditional television systems use channel capacity to transmit a sequence of frames that hardly differ one to the next. The simple-minded proposal to transmit only frame-to-frame differences does not provide an answer. A useful approach is to think of the light distribution on the focal plane of the camera as the 'input,' and that on the display device as the 'output.' These 'video functions' are continuous in space and time. When converted into functions of a single variable by scanning, the redundancy of the video function is incorporated into the resultant video signal, but in a way that makes it very hard to remove. It is more advantageous to work directly with the video function itself.

Since the video function represents continuously moving objects, it must be highly correlated in at least one direction at each point in x, y, t space. One way to think about this is in terms of 'optical flow,' in which we trace the trajectory of moving image points through the space. This naturally leads to ideas such as motion-compensated interpolation, in which intermediate frames or image points can be created from those transmitted at a lower rate if the motion is known accurately. Another way is in terms of the three-dimensional spectrum, which shows a distribution of energy closely related to the direction of motion at each point in space. In both cases, we find that real images never have a uniform spectrum. They contain much less information than arbitrary functions. Substantial economies are therefore possible by using transmission capacity selectively for that information actually present.

Nonuniform spectrum. Conventional video signals exhibit a highly nonuniform spectrum. This is an inherent result of the scanning process as well as the fact that most objects in the scene are much larger than a single picture element. There are two disadvantages to such a spectrum. One is that such a signal cannot use the channel capacity efficiently, since in channels corrupted by white noise, a uniform signal spectrum is essential for high efficiency. Another is that interference performance is poor, since the low signal levels at high frequency are easily perturbed by unwanted signals.

Problems specific to NTSC and similar composite formats. In addition to the previous two issues, which are inherent in all raster-scanned systems intended for transmission in analog channels, there are many specific features of current systems that cause inefficiency and poor performance. Among these are excessively large synch pulses; use of channel time for retrace intervals; vestigial-sideband modulation; use of a separate sound carrier; and the composite signal format, which causes cross effects. Any new system could eliminate most of these problems by using frame stores to separate camera, signal, and display frame rates and to eliminate retrace intervals, by using double-sideband quadrature modulation, and by using time-multiplexing. Certainly, no new system would put color information onto a subcarrier that lies within the video band. Color information would be another component in a time-multiplexed system, with appropriate spatiotemporal bandwidths for both luminance and chrominance chosen as part of the basic system specifications.

New Techniques for TV Transmission Systems

It should be borne in mind that today's system design was fixed nearly 50 years ago, and that color was added 36 years ago. A system conceived with modern transmission concepts and modern components would surely differ in many ways. It is only when we decide to create an entirely new system, not tied to NTSC in any way, that we become free to use the full power of these ideas and hardware.

Smart receivers. It is always a good idea to make the receivers as cheap as possible at the expense of the transmitters. Since, in 1941 and 1953, complexity meant high cost, the receivers were made very simple. An example is the absence of frame stores, which could have been used to eliminate flicker so that a lower frame rate could have been chosen, and so that the retrace intervals could have been eliminated. There is an obvious tradeoff between receiver processing power and bandwidth efficiency. It is inconceivable that a new system would be designed now without frame stores. Likewise, with the enormous progress in semiconductor circuitry, there is no advantage, within limits, in simplifying receiver signal processing, particularly in receivers that will be built by the millions. It would also be very useful to introduce an element of programmability. This would enable receivers to cope with what is very likely to be an environment with even more TV formats than at present. Programmability would also allow the new system to be improved over time without obsolescence, in order to take advantage of improved signal-processing concepts and new components as they become available.

HDTV receivers must be more complicated than today's because, for many years to come, they must be able to cope with NTSC. The best way of doing this is to upconvert NTSC to the HDTV scanning standard, as is planned in the MUSE receivers designed by NHK. The circuitry required to do this can readily be rearranged to make a powerful computing machine that can cope with many different standards. We have coined the term 'open-architecture receiver' (OAR) to call attention to the possibilities of this kind of design. With little or no additional expense, a receiver with these capabilities could be organized with a bus-structured open architecture. This would facilitate interconnection with a wide variety of other devices and communication lines as well as the provision by third parties of plug-in hardware and software modules for additional functionality. The OAR would simplify setting HDTV standards since there would be the possibility of modification after the service was started. It would permit each transmission medium—terrestrial, cable, DBS, fiber—to optimize its own format without the penalty of receiver incompatibility, and it would encourage the provision of additional entertainment, educational, transactional, and informational services that are being so widely discussed for the telecommunications systems of the future.

The OAR concept has not been greeted with much enthusiasm by conventional receiver manufacturers. Companies in the computer, semiconductor, and communications businesses on the other hand, have been more receptive. This points up the fact that there is, potentially, a great deal of money involved in decisions about HDTV. In the current antiregulatory climate, the idea is that the market should make virtually all such decisions. In cases such as this, where the economic interests of the various players do not coincide, it would be remarkable if market decisions were invariably in the interests of the country as a whole.

Subband coding. It was pointed out above that the distribution of energy in the three-dimensional spectrum was highly nonuniform and dependent on motion at each point in x, y, t space. If the space is divided into small blocks, the velocity will be uniform within most of them. Stationary blocks have all their spectral energy on the zero temporal frequency plane. This plane rotates according to the velocity. Thus, in most blocks, much of the spectrum is empty.

If the spectrum is divided into a fairly large number of components, a marked improvement in spectrum efficiency is possible. In general, components can be chosen for transmission that are visually more, rather than less, important. The choice can be fixed, based on the spatiotemporal frequency response of the human visual system, or variable, based additionally on the energy of the components. If the choice is adaptive, it can be on a program-by-program, scene-by-scene, block-by-block, or even point-by-point basis. Adaptive subband coding is an alternative to motion-compensated temporal interpolation, requiring simpler receiver processing. The earliest experiments have been very encouraging.

Adaptive modulation. All the subband components except the ones with a dc value are very small in the relatively blank images areas, where noise and other unwanted signals are most visible. In these areas, the signal amplitude can be considerably increased without channel overload. When the signals are subsequently restored to their original values at the receiver, the noise is reduced by the adaptation factor, which, typically, has a maximum value of 24 to 30 dB. This is not a small effect; it makes possible a major improvement in picture quality under conditions of low CNR.

Information for both adaptive selection and adaptive modulation is transmitted separately, becoming part of the signal description. The effectiveness of these methods depends on the resolution of the transmitted adaptation data—the higher, the better. The adaptation data is highly correlated, and therefore can be efficiently coded, so that the transmission burden is quite acceptable.

Scrambling. All HDTV systems will use frame stores. The transmission process can thus be thought of as sending data from the transmitter memory to the receiver memory, once per transmitted frame. Performing this operation in pseudo-random order, rather than raster order, has many beneficial effects. Encryption is inherent. The scrambling pattern can be changed as often as desired, even on every frame. The spectrum is made uniform, with total energy preserved. All unwanted signals, whether due to echoes, other stations, or even intersymbol interference, are randomized, thus reducing their visibility. Likewise, the visibility of interference caused to conventional signals by a scrambled signal is reduced.

The combination of scrambling and adaptive modulation produces a remarkable improvement in the performance of systems in typical over-the-air channels that are subject to noise, interference, ghosts, and frequency distortion. The transmitted signals look like random noise, so that they have the theoretical possibility of very high channel efficiency. Very high received image quality is obtained at a CNR of only 16 dB, and unwanted interference is rendered virtually invisible at a ratio of desired/undesired signal strength of 12 dB or less. This is to be contrasted with corresponding figures in NTSC of at least 40 and 28 dB, respectively. The consequences of this improvement for spectrum allocation are very favorable. It is believed that, using such methods, all current licensees could be provided with an HDTV channel while, at the same time, a substantial amount of spectrum now allocated to TV could be released for other purposes. During the transition period, when NTSC would still be used on some channels, it may well be possible to use today's 'taboo' channels for HDTV transmission.

The 'data-under' method. The various subbands require different SNR. In digital transmission channels, this is readily accomplished by assigned differing numbers of bits/sample. In analog channels, a similar method can be used, in which the channel CNR can be shared between two components. The first is quantized, typically into four to 16 levels, and the second is added to the first after being reduced in amplitude so as to fit between two levels of the first. These signals can easily be separated at the receiver. Crosstalk caused by channel noise or frequency distortion can be controlled by several effective methods.

Signal packaging to facilitate transcoding. In systems of the general type discussed here, the signal to be transmitted consists of three components (RGB or LC1C2) having a dc value and that must therefore be transmitted digitally, ten to 20 highs (three-D bandpass) components that are to be scrambled and adaptively modulated, adaptation and selection information, audio, and miscellaneous additional data. For any transmission medium, the various components are transmitted sequentially, with the highs components shifted to baseband. A substantial simplification of transcoding from one transmission format to another, and from any transmission format to either production or display formats, can be achieved by grouping the information into packages of nominal length 1/12 second. Each component in each package can thus be thought of as one 'frame' in a 12/frame/second sequence, with a spatial resolution (bandwidth) that depends on the precise way in which the original signal was divided into components. For example, we have found that a spatial resolution of 144 x 256 (aspect ratio of 16:9 with square pixels) is suitable. Components can be combined to achieve whatever spatial or temporal resolution is desired. If 80 components were transmitted (many fewer are required in practice for various reasons) it would be possible to have a resolution of 576 x 1024 x 60 fps. Even higher resolution can be achieved in a single six MHz channel with adaptive selection of components.

Formats of this type can be readily optimized for the various transmission media, both analog and digital. The essential point is to achieve the required CNR for each component, the number of components varying from medium to medium. Transcoding between transmission formats merely requires adding, deleting, and repackaging components, operations that require neither temporal nor spatial interpolation. Conversion to/from production or display formats at 24, 25, 50, 50.94 or 60 fps can be accomplished using integral factors of two, four, or five by off-line adjustment of the program duration by no more than four percent. (If desired, pitch can be maintained on sound tacks by a number of effective methods.)

Some Numerical Examples

Using the methods outlined above, it is possible to configure high-performance systems optimized for various channels. Two examples are given here. The first is for a digital channel at 90 Mb/s and the second is for a cable channel of six MHz and about 36 dB CNR. The examples are for a fixed selection of components with an overall diamond-shaped spatiotemporal frequency response as recommended by Wendland. Each component has a bandwidth of 144 samples/picture height vertically, 256 samples/picture width horizontally, and 12 fps temporally, giving a 16:9 aspect ratio with square pixels. For adaptive component selection, fewer components are used and more channel capacity is devoted to the component-selection data. Higher spatial resolution is achieved than with fixed selection, particularly of moving objects.

A digital system at 90 Mb/s. As shown in the figure, we use 37 luminance components and 6 chrominance components, with bits/sample ranging from eight to two, and averaging 3.91. These components require 74.32 Mb/s, leaving 15.68 Mb/s for audio, synch, adaptation information and miscellaneous data. This gives a spatial resolution ranging from 720 x 1280 at 12 fps down to 144 x 256 at 60 fps. The apparent SNR of the received picture would be very high, but there would be some blurring of moving objects that are tracked by the viewer.

A system for cable. The cable system, shown in the figure, uses 41 components, six of which are transmitted digitally. The six MHz channel is capable of a nominal transmission rate of 12 Msamples/s, allowing for 27 analog components. With the data-under method, 16 components are transmitted in the space of eight, for a total 35, as needed. The 19 components that are not doubled up have digital data transmitted under the analog components. The total digital data rate is 21.23 Mb/s, of which 8.40 Mb/s is used for the six digital components, leaving 12.83 Mb/s for audio, synch, and miscellaneous data. Performance is slightly inferior to that of the 90-Mb/s digital system, but nevertheless of full HDTV quality. If the extra digital data is not sufficient for component-selection information, then fewer components would be transmitted, but higher resolution would be achieved, by adaptive selection of components to be transmitted at each point.

Conclusion

This paper has described a series of modern techniques that can be used in transmitting video information in practical channels, such as over-the-air, cable, DBS, and satellite. These methods allow transmission to be optimized for each kind of channel, and yet permit rather easy transcoding between the various optimized formats, and between the transmission format and production and display formats at all commonly used frame rates. An international program-exchange standard, based on the generic transmission format, could be used equally well by every country without excessive cost or loss of quality.

These technological developments can be used to design a complete television distribution system, from camera to home display, having many advantages over the existing system, or other systems proposed for HDTV. Such systems would provide much better picture and sound quality to viewers under typical reception conditions, would allow evolutionary improvement of the system after installation starts, would free a substantial amount of spectrum for alternative uses, and would not disadvantage any country on account of the domestic TV standard in use.

Acknowledgement

This work is the result of a six-year development program sponsored by the members of the Center for Advanced Television Systems, whose support and encouragement is gratefully acknowledged. Thanks are also in order for the many contributions made by students and colleagues who have participated in the program.

Notes

1. On the other hand, the mass audience really did not want quadraphonic sound or the disc camera. Not every technological innovation is a market success.
2. In this paper, the term NTSC should be read as including PAL and SECAM.
3. Fiber is a special case. Both analog and digital transmission can be used. In either case, composite or component systems are feasible. Satellite transmission also calls for special modulation systems, usually using FM. Digital transmission might be used for DBS.
4. France gave up monochrome high definition for the sake of color. This should tell us something about the relative importants of the two aspects.

William F. Schreiber holds BS and MS degrees in electrical engineering from Columbia University, and a PhD in applied physics from Harvard University. Dr. Schreiber worked at Sylvania from 1947 to 1949, and at Technicolor Corporation from 1953 to 1959. Since then, he has been a faculty member at Massachusetts Institute of Technology in Cambridge, Mass., where he is now professor of electrical engineering and director of the Advanced Television Research Program. He was visiting professor of electrical engineering at the Indian Institute of Technology in Kanpur, India, from 1964 to 1966, and at INRS-Telecommunications in Montreal, Canada, from 1981 to 1982. For over 40 years, Dr. Schreiber's major professional interest has been image processing. He has worked in graphic arts, including color processing and laser scanner design, in facsimile research and in television, including both theory and extensive practical applications. He is a member of The Society of Motion Picture and Television Engineers (SMPTE) and a Fellow of the Institute of Electrical and Electronics Engineers (IEEE). In 1989 Dr. Schreiber was honored by SMPTE for the third time with its Journal Award for Television, in recognition of papers published in the Society's journal.

High Definition Television and the European Community

By Eamon Lalor

This article addresses the subject of high definition television from the European perspective. It is a truly remarkable subject which must be seen in a global context. It is not just a hardware issue, although estimates of the world market for equipment reach into the billions per year, and manufacturers in Europe, in the U.S. and in Japan are deeply conscious of the opportunities and threats involved. It is not just a software issue, although the new technologies underlying high definition will provide marvelous scope for producers of television programs, films and audiovisual software generally to do exciting new things. It is not just a user issue, although the enhanced experience—equivalent to cinema quality for the pictures and compact disc quality for the sound—will be a revolution of striking proportions for the viewing public.

Again, it is not just a hardware issue or a software issue or a viewer issue. It is all three—but in addition it has also become a cultural and a political issue. It is a cultural issue because the well-recognized power of TV to reflect and influence cultural values will be enhanced with high definition. It should not be forgotten that the European Community is a community of 12 countries with diverse cultural backgrounds. Television, and particularly HDTV, offers the possibility of enhancing this rich cultural heritage by giving all in the Community access, in a striking manner, to others' cultural contributions.

The political interest in Europe may be judged from the fact that when the heads of state and government of the European Community met in December, 1988 they accorded it a high priority. The Council of Ministers of the Community has also recently adopted a council decision on HDTV. This article will explain how HDTV has become a topic of such importance to Europe; what role the European Commission has played; and what further activities are planned.

TV in Europe: Towards Deregulation, Competition and Pan-European Broadcasting

Broadcasting in Europe is in a ferment of change. The previously comfortable environment of the state-funded public sector broadcasters is under pressure from commercial forces. These commercial forces are internal—as networks are increasingly forced to fund their operations and development from their own resources and without government subvention, and external—as new private operators seek to gain market share at their expense, either employing conventional terrestrial broadcasting technology or, more commonly, the technology of satellites. The increasing deregulation of TV in Europe, together with increasing competition to provide services, will result in more service volume, new kinds of services and, it is hoped, wider consumer choice.

Direct-to-home satellite technology dismantles national boundaries. Up to 30 new TV channels will be made available in Europe in this year and the next from DBS or quasi-DBS satellites. These satellites will not respect borders. Pan-European TV broadcasting will begin. The birth of Pan-European broadcasting will not be easy. The 12 member states of the Community have different cultural traditions, different legal system and nine different languages. The process, however, is inevitable and it has begun.

Direct Broadcasting by Satellite: MAC, The New Technical Standard

Since the introduction of color, Europe has had a problem in television that exists neither in North America or Japan: the existence of two technical formats side by side, PAL and SECAM. Each of these separately is in fact superior in quality to NTSC, but this situation has also presented some inconvenience in economic and technical terms.

The prospect of DBS in Europe offered a way out of this problem. The technical work of the Broadcaster's laboratories (notably the U.K. IBA) and the standardization work of the European Broadcasting Union (EBU) resulted in the definition of a new format (MAC/packet) ideally suited to the new medium.

Multiplexed Analogue Components (MAC) is a component rather than a composite system which allows significant quality improvement due to the elimination of cross-interference effects between chrominence and luminance, leading to a better picture (compared to PAL, SECAM or NTSC) with better color rendition. The packet relates to multiple channels of digital sound—CD quality sound. The multiple channels are important in the context of European multilingualism. The efficient use of energy in this system makes it ideal for satellite use.

In addition to the advantages already mentioned there is, however, another of overwhelming importance—and that is the technical evolutionary possibilities of the system which will allow new features and higher quality to be added naturally. Among these new features it is worth mentioning:

1. The possibilities for encryption, which will be of increasing importance with the expected growth in Europe of subscription TV; and
2. A new 16:9 aspect ratio similar to that of the cinema.

The quality evolution can go all the way to high definition in a backward-compatible manner which is crucially important for the Europeans and which I shall emphasize again below.

In summary, the above advantages are of such an overwhelming nature that the 12 member states of the Community unanimously adopted the MAC/packet family for high power DBS and subsequent cable redistribution. A community directive, binding on all member states, was adopted.

The MAC system will be introduced in Europe this year and next through the French TDF-l (and possibly 2); the German TV-SAT 2; the U.K. BSB direct broadcasting satellites and some channels of the medium-powered ASTRA satellite. The signals will be received by means of an antenna and satellite tuner on either new MAC TV sets or on existing PAL and SECAM sets with the addition of a low-cost MAC converter. The low cost is important as it is a firm article of faith in Europe that each succeeding evolutionary step in TV should not disenfranchise the existing viewers by making their equipment obsolete. Each new generation of service must be receivable by the existing installed TV set and VCR population without significantly increased cost.

High De&Mac222;nition Television in Europe: Compatible Evolution Through MAC

In the first half of the 1980s when HDTV was being discussed in technical television circles and in the international standardization forum (the CCIR), there was an emphasis on the adoption of a world standard for HDTV production and program exchange. The Japanese NHK offered its system based on 1125 lines and 60 frames per second interlaced scanning as a candidate for such a standard. At the same time, Japan offered the bandwidth-reduced system MUSE as a transmission standard; but the debate in the U.S. focused mostly on the production standard.

The European analysis was different. It started from broadcasting, not from production. The results of this analysis were very clear. Europe wanted an HDTV transmission standard that was compatible with existing receivers. It was unthinkable that a new generation of TV services would make obsolete the existing installed base of receivers and surrounding infrastructure such as VCRs and camcorders. Europe therefore emphatically rejected the MUSE transmission system because it would lead to just such an obsolescence, being incompatible with all existing TV standards whether PAL, SECAM or NTSC. Europe saw the future as an evolution of the existing MAC system to a high definition MAC standard for HDTV transmission.

The next aspect of HDTV to be considered in Europe was a production system. The requirements here were identified inter alia to be:

1. The chosen system must have sufficient "headroom" to allow conversion to the European high definition transmission standards (now defined as HD-MAC) with full high definition quality.
2. The chosen system should be easily convertible (both ways) with the existing world standard for high definition, namely 35mm film.
3. The chosen system should be of sufficiently "high definition" to be a credible replacement ultimately for film itself. It should in fact be an advance on film as an orgination system in that it should build in the greater flexibility offered by electronics in facilitating the (digital) manipulation of the images.

When the Europeans examined the NHK 1125/60 system against these requirements, the answer was clear. The NHK system did not meet any of the specified requirements: it did not have enough headroom to convert adequately to HD-MAC. The 60 Hz field rate caused unacceptable difficulties in converting to 24/25 frame per second film; the system was not of high enough quality to replace film and the interlaced nature of the system precluded digital manipulation of the images.

Europe's response to the NHK proposals was therefore emphatic. The proposed 1125/60 system was unacceptable as a single world standard for HDTV production and program exchange. Europe therefore set itself the task of defining appropriate transmission and production standards to meet all these criteria.

To achieve this, the Eureka-95 HDTV project was undertaken. This project is being carried out by a consortium of more than 20 European companies, led by the major European consumer electronics firms: Philips, Thomson and Bosch. This work has progressed satisfactorily and the parameters of the new system are now well defined and agreed-upon. They are, for the ultimate HDTV production standard: 1250 lines /50 Hz /16:9 aspect ratio /1:1 progressive scanning.

This is the standard that would apply for international program exchange and for two-way conversion with film and digital video tape. It could ultimately replace film as the high definition production standard. A certain amount of production could, however, be undertaken for local use with a somewhat less rigorous standard: 1250 lines / 50 Hz / 16:9 / and either a filtered progressive scan 1:1 or an interlined scan 2:1. The emission standard would be: HD-MAC-1250 / 50 / 16:9 / 2:1.

The definition of the above European system is one thing, but what about the necessary equipment? Here also great progress has been made and some equipment has already been announced and shown.

In fact, the whole chain of European HDTV production, transmission and display was successfully demonstrated in September, 1988 at the International Broadcasting Convention in Brighton, U.K., and subsequently at Montreux and Berlin in 1989. The evolution of the European system towards commercialization can be clearly seen through this sequence of major demonstrations. By August, 1989, at the Berlin IFA the emphasis was changing from equipment (where in fact, many new advances were also shown) to the production of HDTV programs. The focus of the effort will now shift from the development of technology and equipment progressively to the use of the system and the creation of HDTV software.

The Berlin project, which was an ambitious one including a specially-built HDTV production studio, is a good example of the initiatives which are needed in HDTV production in order to establish a solid base for European HDTV. This particular project, initiated through Eureka-95 with the support of the European Commission, brought together seven broadcasters working in cooperation with a German production team to make and show full-length HDTV programs (15 to 20 minutes each).

The programs were a long way from the first demonstration clips, using to the full the capabilities of the system to make programs ranging from sports coverage to light entertainment, drama and documentaries. They brought spectacular color, vivid sound and immediate images in a demonstration of the unique features of HDTV production.

The evolution of HDTV has now reached the point where the production industry has a crucial role to play in contributing to the fine-tuning of the equipment and in the lead up to the introduction of HDTV services. This means that as we move towards the consideration of a world HDTV production standard in the CCIR in the autumn of 1990, there is a situation radically different from that which prevailed in Dubrovnik in 1986.

Europe has made substantial progress over the last three years. Not only has a theoretical HDTV standard been developed, offering a compatible road towards its implementation, but the feasibility of this standard has also been fully demonstrated with all the necessary equipment on a number of occasions. It is with confidence that we seek to continue an international dialogue, as we prepare for entering the new phase of bringing HDTV to the market.

Where Do We Go From Here in Europe: From R&D to Service Introduction

What about the future? What are our plans and intentions? I remind you that in April, 1989 in Luxembourg, the council of ministers—including the Ministers of Telecommunications of all our member states—adopted a decision on high definition television. The decision in effect establishes the outline of a comprehensive strategy for the launch of HDTV services in Europe—and here I don't limit myself to the Community: other European countries must also be involved.

This strategy is articulated in five objectives, which I would like to discuss one by one.

1. To make every effort to ensure that European industry develops in time all the technology components and equipment required for the launching of HDTV services. We foresee the Eureka-95 project continuing its work and broadening its base of participation to include other industries and other countries. We see the European Community being even more closely involved in this work and we intend to make resources available to it from our existing RACE and ESPRIT programs.

2. To promote the adoption of the European proposal based on the 1250 lines, 50 complete frames per second progressive scanning parameters, as the single world standard for the origination and exchange of HDTV program material. It is clear to us that this is the best candidate for a single world production standard on offer. It will be necessary to convince the future users of the related equipment—not only in Europe but around the world—of this before there will be unanimous agreement on this proposition.

If we are to have another five years before the unique production standard is adopted, then this time will have to be well used by making as much finished equipment in the European standard available to users, as possible. Of particular importance in this regard will be the film production industry.

3. To promote the widest use of the European HDTV system throughout the world. In this stage of transition until the commercial introduction of HDTV—expected to begin in Europe in 1992—a number of measures will be undertaken to prepare the market at the user end. Users are considered at two levels: professional users (program makers and service providers), and end users (viewers).

In this transition period, a number of productions and demonstrations will be undertaken in Europe using HDTV. Particularly targeted will be major sporting events, such as soccer's World Cup in Rome in 1990, and the Olympic Games in Albertville and Barcelona in 1992. In addition, planning is underway to make the new equipment available to program professionals for experimental productions.

Let me be more explicit on how we propose to organize this effort. From a previous decision of the Council, a European Economic Interest Grouping (EEIG) has been established. This is a flexible mechanism working transnationally to allow partners from different member states to pool their resources to achieve objectives in their common interest.

It is envisioned that one of the first EEIGs will concern HDTV. The members of this grouping will be firms from consumer and professional equipment manufacturers, broadcasters, film makers and audiovisual software production houses. The HDTV-EEIG will play an important role in making (fixed and mobile) production facilities available to professionals in the film and TV program production world. It will also organize and mount demonstrations of the European system on suitable occasions and it will provide written and audiovisual material explaining the merits of the system.

4. To promote the introduction, as soon as possible (and in accordance with a suitable timetable from 1992) of HDTV services in Europe. The introduction of services —whether they are delivered to the viewer's homes by satellite, by cable or by terrestrial link—is the ultimate aim. All other initiatives should lead to this.

The coordinated introduction of these services at the European level is necessary. Many different actors will have to work together, both within their own countries and transnationally, if this is to be achieved. In this connection, I speak of the equipment manufacturers, both consumer and professional. I speak of the producers of programs and films, whether they are broadcasting organizations or independent production houses. I speak of providers of television services whether they are public service broadcasters, private broadcasters, satellite distributors or cable operators. I speak of government authorities who have substantial interests in this subject. And I speak of the final users—the viewers—at whom these services are ultimately targeted.

5. To make every effort to ensure that the European televison and film production industry achieves the capability, experience and dimension required to occupy a competitive position on the HDTV world market and to allow the member states to make their own cultural contribution.

HDTV offers an opportunity for the European TV and film industry to establish a competitive position within the world market. In order to benefit from this opportunity, experience, competence and scale of operation in HDTV production need to be fostered and developed here in Europe. Projects such as the Berlin productions which I mentioned earlier and the EEIG initiative will go some way towards starting the process. However, the real impetus will come from the cooperative relationships within the production industry as much in training and experimentation as in co-financing and co-production.

I repeat that these five objectives provide a framework for a comprehensive strategy leading to the introduction in Europe, as soon as possible, of HDTV services. The Commission intends to work very closely with the principle actors concerned—industry, broadcasters and governments—to ensure that this aim is achieved rapidly and effectively.

I have offered the European perspective on HDTV developments. I have attempted to explain both what we are doing and why we are doing it. I have emphasized the complexity of the issue and the nature of the international debate, which is not always easy. We in Europe are now leaving the technology phase and are entering the challenging and exciting phase of preparation for implementation and market introduction. A major cooperative effort will be made in Europe over the next few years for the successful achievement of this objective.

Let me emphasize, however, that we are not inward-looking in this regard. On the contrary, we also stand ready to cooperate with partners in other parts of the world in moving as rapidly as possible towards the day when high definition television pictures will be routinely viewable in all homes.

Eamon Lalor holds a PhD in physics from the University of Rochester, New York. He has held teaching positions and conducted research in physics in universities in Ireland, Italy and the United States. In 1973, Dr. Lalor joined the Irish National Science Council, where he was responsible, among other things, for energy research and development policy. More recently, he has served as head of information technology and space at the Irish National Board for Science and Technology. In 1986 he joined the European Commission as head of division, responsible for space and terrestrial infrastructure and audiovisual technology. This division is under the auspices of Directorate General XII: Telecommunications, Information Industries and Innovation. Dr. Lalor's current responsibilities include the Commission's policies and activities in high definition television.

The subject of this article is the ten biggest HDTV myths. Narrowing the list to ten was a most difficult task because HDTV is, by far, one of the most misunderstood subjects of all time. The level of confusion—in Washington, in the media and within the many industries with a vested interest in HDTV—is nothing short of a phenomenon. Therefore, I set out to debunk some of the myths surrounding this otherwise exciting technology.

Myth #1—U.S. television sales are dominated by Japanese companies. This is simply untrue. Several of the largest U.S.-owned firms in consumer electronics were, indeed, purchased by foreign firms. RCA was purchased first by General Electric in 1985, and then sold to Thomson of France in 1987. Philips of the Netherlands purchased Magnavox in 1975, and Philco and Sylvania in 1981. Zenith remains the only major U.S.-owned producer of TVs. In 1988, Thomson, Zenith and Philips accounted for well over half of all color TVs sold in the U.S. The rest of the market was divided by more than a dozen Japanese and Korean producers.

Despite the increased participation of foreign-owned firms in the U.S., the domestically-manufactured content of the average color TV made in the U.S. in 1987 was estimated at 70%. And the percentage has increased since that time. Furthermore, over 80% of all large TV screens for the U.S. market are built in America.

Yes, foreign-owned manufacturers even export color TVs from the U.S. to foreign markets, even to the Far East. And, foreign-owned color TV manufacturers provide over 20,000 jobs to U.S. workers; that's ten times the number provided by Zenith, which has more foreign than domestic manufacturing installations.

Myth #2—All Sony television sets are made in Japan. This is hardly true. Better than 85% of all Sony TVs sold in the U.S. are made in the U.S. And yes, Sony is among the companies which export TVs from the U.S. to Japan. HDTV receivers would most definitely be made in the U.S. because of their large screen size. In my view there will be significant domestic content in these HDTV sets.

Myth #3—The 1125/60 production standard is a Japanese standard. This is not true. The current HDTV production standard that has been approved by ANSI was developed over a five-year period by the Society for Motion Picture and Television Engineers (SMPTE), the standards-making organization for film and television engineering in North America. This standard was reviewed and recommended by the Advanced Television Systems Committee (ATSC), an American private sector organization, to the U.S. State Department. Over 267 U.S. and Canadian engineers participated in the process.

Many changes were made from the original research that was done by NHK in Japan. For example, the original NHK proposal called for 1125/59.94. Such a standard would have been much more saleable to the U.S. broadcasters. However, U.S. engineers recommended 1125/60 as a more attractive standard for possible worldwide acceptance.

Myth #4—A worldwide HDTV production standard is unattainable. Based on the current level of confusion and nationalistic rhetoric, it's true that this will be most difficult to accomplish. But, there is still a desire among world broadcasters for a single standard. As long as that desire exists, the possibility for one standard exists.

However, even if we fail to choose a single worldwide standard, 1125/60 is still the best standard for the U.S. by virtue of the transcodability of this standard and its easy conversion to film. The 85% world market share of the Hollywood production community will be preserved.

Myth #5—HDTV is a monolith that includes production, transmission and display. The world engineering community has never viewed it this way. From the very beginning there was agreement that production, transmission and display were separate issues. Establishment of an HDTV production standard has very little to do with how signals are sent or how pictures are displayed. Witness 35mm film, the only existing worldwide production standard. Do you watch 35mm film at home on film projectors? Does it have a signal that you can distribute electronically?

Myth #6—The 1125/60 HDTV production standard is unsuitable to U.S. terrestrial transmission plans. After all, isn't it the same as the Japanese MUSE? This is a very distorted statement. MUSE, which stands for Multiple Subnyquist Encoding, is a means of transmitting a TV signal. It so happens it is the system being used in Japan for transmission over satellite. There is absolutely no technical relationship between the 1125/60 production standard and MUSE. Even if Europe chose to apply MUSE to their standard instead of MAC they could do so.

As to 1125/60's ability to be converted to NTSC for U.S. broadcasting, it has been successfully demonstrated. How about PAL in Europe? Conversion has also been demonstrated. Has any other standard demonstrated this easy convertibility? No. No matter which transmission system is selected for U.S. broadcasters, 1125/60 can easily be converted for signal distribution. This conversion is no more difficult than the conversion process all 35mm films undergo before they are transmitted over NTSC and PAL.

Myth #7—1125/60 is a non-digital system. This is not at all true. Current broadcast transmission standards are based on analog systems The current 1125/60 production standard was designed to interface with today's transmission system. That does not mean it is non-digital. Several manufacturers are already demonstrating digital HDTV VTRs and others are designing HDTV digital effects systems.

Myth #8—Eureka is compatible with existing European terrestrial television service. This is not really the case. The 1250/50 standard was designed to be compatible with MAC, a satellite—not terrestrial—transmission system. But MAC has not been accepted throughout Europe and is not currently in use.

Myth #9—Viewers cannot see the difference between HDTV and standard TV pictures. In response to this, I will quote some comments recently made by James Monaco, founder and president of Baseline (an online information service for the entertainment industries), and the author of numerous books about film and the media. In an article appearing in American Film, he states:

"Although there are several competing standards, I've seen the Sony 1125-line HDTV image and I'm here to tell you that this is really something special. What Cinerama pretended to be, HDTV is. Although the resolution is more than twice the current American standard, the psychological effect is nothing less than breathtaking. If you're nearsighted, take your glasses off. That's the American television standard today. Now put them on. That's HDTV."

Monaco goes on to describe the fact that detail now counts for more than atmosphere within a picture frame: "You realize that the reason for the classic close-up and two shots during the last 90 years of film history is that that's all anyone could effectively show. Now you can see the forest as well as the trees. Indeed, you can see the leaves on the trees." There will always be critics of new technology. But you can't make a blanket statement that viewers cannot see the difference.

Myth #10—A unique U.S. standard is necessary for U.S. industry. I believe that 1125/60 is as much an American production standard as it is Japanese, if not more. In fact, the inventors were dismayed at the changes made by North American experts to the original NHK proposal.

Beyond the matter of who gives birth to an idea and where the research is done, leadership in HDTV will be based on the application of this technology. Frankly, I believe it is a total waste of time and effort for the U.S. to start over and not make use of the years of research and development that have already taken place. After all, Japanese and European industry had no trouble manufacturing U.S.-invented NTSC. Failing to take advantage of the work that has already been done may leave the U.S. behind both Japan and Europe in its ability to put HDTV to practical use, and reap its benefits both economic and technological. And by the way, neither 1125/60 nor SMPTE 240M is patentable.

1125/60 HDTV is a technology designed for use by diverse industries. It is not like the broadcast-only technologies being suggested by some U.S. broadcasters. It is a technology that can be used by the motion picture industry, computer graphics, printing and medical imaging fields, as well as broadcasting. It presents far more business opportunities for U.S. companies than do any other proposed standards. And that means growth for the U.S. economy. As a representative of Sony Corporation of America, I say it's time to stop the squabbling over HDTV and put America's best minds to work on how to make it work for U.S. industry and U.S. consumers. Above all, let's not settle for technology capable of only limited applications and limited bene&Mac222;ts. Let's utilize the work that has been accomplished and build upon it with American innovation.

William G. Connolly is president and chief executive officer of Sony Advanced Systems. From 1986 to 1988, he was president of Sony Communications Products Company; and from 1983 to 1985 he was president of Sony Broadcast Products Company. Before joining Sony, he held various positions during a 23-year career at the CBS Broadcast Group, including director of development, vice president of development, and vice president/deputy director of engineering and development. During his time at CBS, he was responsible for development of all new production and broadcast equipment and systems used by the CBS Broadcast Group (network, news and stations). Prior to CBS, Mr. Connolly worked in the automation applications department of the Western Union Telegraph Company. He has received professional awards that include the National Association of Broadcasters (NAB) Engineering Achievement Award in 1989, and a series of Emmy awards while at CBS and Sony for the development of various technologies for television and film. In addition, he is a Fellow and former member of the board of governors of the Society of Motion Picture and Television Engineers (SMPTE), and served as the chairman of its working group on digital television tape recording. Mr. Connolly holds a BS in mathematics from Columbia University, and served a four-year tour of duty with the United States Air Force.

Introduction

The standardization work of the CCIR (a French acronym for the International Radio Consultative Committee) is carried out in 13 study groups consisting of about 1100 participants drawn from member telecommunication administrations, broadcasters, operating companies, industry and international organizations. Much of the work is done by small working parties and by correspondence, but formal adoption of CCIR reports and recommendations takes place during full study group meetings, held every two years, followed by a plenary assembly, to complete a four-year study cycle.

There is a small, specialized technical secretariat located in Geneva, Switzerland to assist the elected director and study groups to carry out the work. The present director, Richard Kirby, was recently re-elected by the ITU Plenipotentiary Conference held in Nice, France for a five-year term.

Television Systems Development in the CCIR

CCIR studies in television standards began in 1948, to permit "interchange of programs on the widest scale." Television systems development work is principally carried out in CCIR study group 11: broadcasting service/television. Baseband and emission standards are dealt with, as well as recording and satellite broadcasting. The latter two areas are treated jointly with study group 10: broadcasting service/sound.

The CMTT (joint CCIR/CCITT study group dealing with the transmission of television signals) works closely with study groups 10 and 11 in these areas. The CCIR study group activities in television also deal extensively with spectrum utilization, i.e., protection ratios, interference and sharing with the other radiocommunication services. There is an increasingly strong relationship between broadcast and non-broadcast activities, and particularly their equipment and specifications, mainly with respect to consumer and telecommunication applications, as well as computer/data-processing applications. CCITT study groups dealing with the broadband integrated services digital network (ISDN) are concerned with telecommunication network system standards, the IEC is dealing with equipment standards, and the IEC and ISO jointly deal with information technology standards. CCIR maintains close liaison with these activities.

Why is HDTV of Interest?

HDTV offers the possibility for the first time to provide the individual television viewer, in the home, with large-screen quality and realism equivalent to high-quality cinematography. In addition, major applications are foreseen in cinema-type production and projection.

What is HDTV?

The current CCIR studies consider HDTV to have about double the horizontal and vertical resolution of conventional 525- and 625-line standards, and a wide screen aspect ratio. There is, in large, agreement on a 16:9 aspect ratio for HDTV, as compared with 4:3 for today's systems.

Although the CCIR considers that HDTV implies large screen display of cinema quality, using more than 1000 lines, the term HDTV is being applied to all sorts of new television systems. State-of-the art HDTV systems offer resolution comparable to that of 35mm cinema film, do not contain the signal degradations existing in present-day color television systems and do not suffer from significant degradation in resolution for moving objects (i.e., smearing). This latter point is especially important, but is difficult to quantify and evaluate. Vertical resolution is assumed to be more than 1000 lines, with comparable horizontal resolution. The resulting unprocessed baseband signal requires about four times as much bandwidth as conventional television signals. There is general agreement that HDTV includes one or more stereophonic sound channels that provide quality comparable to that of compact disks.

The description of high definition television given in CCIR Report 801-3 was agreed upon during the 1989 meeting of CCIR study group 11 on high-definition television: A high-de&Mac222;nition system is a system designed to allow viewing at about three times the picture height such that the system is virtually, or nearly, transparent to the quality of portrayal that would have been perceived in the original scene or performance by a discerning viewer with normal visual acuity. Such factors include improved motion portrayal and improved perception of depth.

Why Standardization?

The first question that has to be answered is, Why standardization? Why not just let HDTV develop as it comes? Eventually one or more systems will gain widespread acceptance and will become de facto standards.

The answer to this question is obvious. One has only to consider existing television systems. Three major color standards in the world (NTSC, PAL and SECAM) and some 16 variations make it difficult to produce and exchange programs in the global marketplace. Standards converters are expensive and often result in serious quality degradation. Even though excellent quality productions are done in videotape in each of the systems, 35mm film is often the favored way to move from one system to another without serious quality degradation. Degradation resulting from standards conversion will likely be even more critical in HDTV.

Broadcasters, program producers and consumers have the most to lose from multiple, hard-to-convert different standards. With global standards, receiver manufacturers will have global markets instead of fragmented, smaller local markets. Once the desirability of standardization is accepted, the timing and nature of standardization become critical issues. Set a standard too soon or too rigidly and important technical advances may be precluded. Set it too late, and a proliferation of incompatible systems will enter the marketplace. The nature of HDTV standardization is especially complicated.

Definitions

Several definitions from the CCIR work are important to this article.

HDTV emission and transmission. The term emission is used to indicate over-the-air broadcasting, and the term transmission is used only with one-way point-to-point links.

Conversion and transcoding. The term conversion is used when a video signal is changed from one scanning standard to another (e.g., line-rate conversion, field-rate conversion, or both). The term transcoding is used when the video signal is changed from one form of encoding to another, without changing its scanning parameters.

Compatible. A new emission standard is compatible with an already existing emission standard if signals according to the new standard can be received and displayed without additional equipment, with receivers designed for the existing standard. The quality should be about the same as when a signal according to the already existing standard is received.

Evolution. The term evolution is used to denote a smooth and gradual transition between one broadcasting service and another, which follows it in time.

Until recently, the CCIR work was focused on a unique, global studio standard. This would permit the production, exchange and distribution of HDTV television programs worldwide. Emission standards for broadcasting (i.e., single transmitter to multiple receivers) and transmission standards for distribution were not involved. More recently, the CCIR work has also taken on emission and transmission standardization. The immediate goal of study group 11 remains to develop a unique studio standard.

The development of an HDTV studio signal format is a comparatively straightforward engineering task. The development of HDTV signal formats for terrestrial and satellite broadcasting, for cable distribution (coaxial and fibre-optic), for videocassette machines and for optical disc distribution is extraordinarily complex, especially if inter-media compatibility and source-signal quality are goals.

For broadcasters, at least, the necessity of a single, global studio standard was so evident that the Fourth Conference of World Broadcasting Unions (Algiers, 1983) requested the members of its broadcasting unions to coordinate their studies on the characteristics of a unique worldwide standard for HDTV. This was reflected in decision 58-l prepared by CCIR study group 11 and approved by the XVIth CCIR Plenary Assembly (Dubrovnik, 1986), which considered that "it would be beneficial to HDTV broadcasters and to the public alike if the CCIR could recommend the adoption of a single, worldwide standard for high-definition television."

Clearly, considerable benefits would accrue, particularly to the global public, if a single worldwide standard, or a family of easily-convertible standards applicable to the production, transmission and emission media (satellite and terrestrial) were available. The resulting economies of scale in the production and delivery of programs, as well as in the production of receivers, offer major benefits to all participants, from program producers to viewers:

Benefits to program producers:
1. One video production for a worldwide audience.
2. Wide availability of source material that requires no conversion.
3. High-quality electronic editing and special effects.

Benefits to studio equipment manufacturers:
1. Global market available.
2. Wide availability of components and peripherals.

Benefits to program distributors:
1. Worldwide distribution facilitated.
2. Possibilities of direct access to cinemas.

Benefits to broadcasters:
1. Access to a global pool of high-quality video program material directly usable without conversion and the associated extra costs and technical degradation.

Benefits to receiver manufacturers:
1. Global market available.
2. Reduced impact of local market fluctuations.

Benefits to viewers:
1. Access to a global pool of high-quality programs.
2. Reduced receiver costs thanks to global competition and economies of scale in production.

Conversion among multiple standards increases cost and reduces quality. The substantial real and hidden costs of the existing plethora of television systems are paid by the viewing public, producers, broadcasters and cable operators. (CCIR Report 624 gives the characteristics of 16 major variations of color television video systems). Equally important is the loss of profits that could have been achieved by receiver, studio and emission equipment manufacturers, broadcasters and cable system operators, had there been a single worldwide standard.

In addition to the costs, numerous technical compromises in quality have been necessary when converting from one system to the other. Even today, conversions between 525-line NTSC and 625-line PAL or SECAM signals, or vice-versa, often result in less-than satisfactory pictures.

The process of international standardization offers, in principle, the possibility for each of the major players in the game to advocate those features which are most individually advantageous, and to arrive at a reasonable compromise that takes into account those which are important to the others.

HDTV vs. Conventional Systems

Some arguments center on whether or not the viewing public will find the technical advantages of high-definition television sufficiently attractive to invest in expensive new receivers. Present trends indicate that this is, at most, a short-term question, for two reasons. First, the average screen size of newly-purchased television receivers is increasing. This trend, which has been evident in Europe for several years, has recently taken a very sharp upward direction in North America and Japan. Receiver manufacturers are consequently resorting to a number of techniques to improve the apparent definition of big-screen displays, which suffer from noticeable line structure when conventional 525- and 625-1ine signals are displayed. Next, the life of a color television receiver is between five and ten years. Hence, almost everyone will have replaced existing receivers before 2000, whether or not HDTV is introduced. Because of this, "buying HDTV" becomes an incremental cost.

Display size and viewing distance are important elements in the perceived quality of HDTV. Viewers generally do not notice great improvement in quality when viewing HDTV programs on small screens of 50 cm diagonal dimension, or less. Valid viewer reaction tests should employ displays of 100 cm or more, at a viewing distance of about three times the picture height, for both the HDTV system and the conventional system with which it is being compared. Under these circumstances, HDTV systems are given high ratings.

Another key point to keep in mind is that full-quality HDTV will only be available to viewers who have purchased new receivers, regardless of the standard or standards ultimately adopted. Compatible HDTV emissions (see definition above) could be received on existing receivers, but the viewer would obtain a signal comparable in quality to that obtained from a conventional emission.

The pace of the standardization work is largely dependent upon the expected time frame for large-scale introduction of HDTV. A few years ago, broadcasters perceived an urgent need to obtain the ability to broadcast HDTV signals, in order to short-circuit pre-emption of their future markets by satellite broadcasting, by videocassettes and by broadband fibre-optic networks. The spectre of the enormous success of compact-disc technology in a short time span was hanging over the industry.

Now, it is clear that the time span for introduction of HDTV will more closely follow the model for color television. Ten or more years will likely pass before there is large-scale consumer acceptance of HDTV. The major reasons for this are cost, size and weight.

To obtain the real benefits of HDTV, a large-screen display is required, with a diagonal dimension of about one metre (>three feet) or more. To obtain the luminance levels required for viewing in a normally-lighted room (as is the case with current color television displays) presently requires a cathode-ray tube display. Such displays may weigh more than 100 kg (220 lb) and cost more than $3500. It is physically impossible for most consumers to install or move such displays. Widespread consumer acceptance will require the availability of a high-luminance flat-panel display of reasonable weight. Projection displays will offer an intermediate solution, but presently require more space than is available in most living rooms.

Keeping in mind the time frame for consumer acceptance of HDTV, it is reasonable to predict from the present trends in technology that digital processing will be the heart of the 21st Century television display. The CCIR work is now oriented in that direction. It is important to keep in mind the convergence of television and computer technology in the informatics society of the next century.

In North America, Japan and a number of other countries, the field frequency for conventional color television systems is 59.94 Hz and there are 525 lines per frame. In most of the rest of the world, the field frequency is 50.00 Hz and there are 625 lines per frame. 2:1 indicates interlaced scanning, whereas 1:1 indicates progressive scanning. For convenience, these are designated as follows: field frequency/number of lines/type of scanning, or 59.95/525/2:l and 50/625/2:1.

The existing line and scanning standards pre-date colour television and were set relative to power line frequencies that exist in various parts of the world. There is no longer any reason for scanning standards to be related to power line frequency. (Japan has always been an exception, where both 50 Hz and 60 Hz power line frequencies exist.)

Perspective

As if the technical problems were not enough to keep the CCIR study group's 11 specialists fully occupied, economic and political issues have entered on the scene. A summary of how the current situation developed will be useful. There are four separate, though interrelated, areas for standardization in television: (1) studio standards, (2) exchange standards (including recording and transmission), (3) emission standards and (4) display standards.

There has been considerable controversy, still largely unresolved, about priorities. Should studio standards be developed first, followed by system specifications in the other areas, derived from the studio standard, or is it more realistic to set emission system parameters first, and establish system specifications in the other areas based on achievable emission formats? How should exchange or display formats be related to studio or emission standards?

The Japanese, under the leadership of Dr. Fujio of the Japanese national broadcasting system, NHK Research Laboratories, started development of an HDTV studio system more than ten years ago. Based on analog technology, this system had reached an advanced stage of development and implementation by the time of the 1985 final meeting of CCIR study group 11. Certain critical system parameters, such as field rate, had been adjusted to meet U.S. requirements. The resulting system was proposed by the Japanese, with support at that time from the U.S. and from some European broadcasters, as the unique world studio standard.

Europe, in the meantime, had been preoccupied with the development of an advanced television emission standard intended primarily for satellite broadcasting. Intended to eliminate the annoying artifacts in PAL and SECAM systems and to provide multiple high-quality audio and data channels, the multiplexed analog component (MAC/packet family) systems provide the same 625 lines of resolution and a conventional 4:3 display, with the potential for upgrading. MAC signals require a converter or adapter to be viewed on an existing PAL or SECAM receiver.

The first MAC systems began experimental operation this year with the launch of the high-power French direct-broadcasting satellite TDF-1. The Federal Republic of Germany will initiate similar broadcasting later this year when an identical satellite, designated TVSAT and recently launched, is commissioned.

Starting in 1985, Europe, and particularly European industry, began to take an intense second look at the strategy for the introduction of advanced television systems. Concerned that the adoption of the Japanese-conceived studio standard would jeopardize the future of the European television industry, the western European nations banded together in a well-funded technology development project, Eureka-95. The principal objective of this project is to produce a completely new HDTV system, from studio to receiver, including both professional and consumer videotape machines. Also largely based on analog technology, the system is now well advanced, and demonstration units of all its major elements were shown at this year's international television exhibition in Montreux, Switzerland.

The European and Japanese approaches are similar in the sense that signals broadcast in the HDTV standard require an adapter to be received with conventional-system quality on existing television receivers. There is a major difference in strategy, however. The Japanese envisage going directly from conventional systems to HDTV without any intermediate steps. They have already implemented satellite HDTV emissions using a modulation system named MUSE, with baseband video signal parameters compatible with the NHK-designed studio signal standard.

The Europeans involved in the Eureka-95 project are following the strategy adopted several years ago, in which conventional terrestrial broadcasts are to be replaced with satellite-based MAC/packet broadcasts. These are to be received directly with small parabolic or flat-plate antennas or via coaxial or fiber optic cable systems. During this first phase, conventional terrestrial transmissions will presumably continue until most existing receivers are replaced with MAC/packet receivers. In the second phase, high definition MAC signals will replace the conventional MAC signals. HD-MAC is designed to be compatible with conventional MAC so that existing MAC receivers will be able to receive the new HDTV signals with conventional-MAC quality, and HD-MAC receivers will be able to receive both kinds of signals. The European strategy obviously was intended to cover a long time span, in that a completely new, intermediate-technology system was to be introduced, used and phased out before HDTV was extensively introduced. There now seems to be some compression of the time frame.

When the 1986 plenary assembly of the CCIR considered the proposal for a world studio standard, based on the NHK work, there was opposition, particularly from European participants. Consequently, a decision was deferred to the 1986-1990 study period.

The two proposals for a studio standards currently before the CCIR are: 60.00/1125/2:1 (NHK design) and 50.00/1250/1:1 (Eureka-95 design). The 50 Hz system is initially being implemented in the con&Mac222;guration 50/1250/2:1.

Particularly during the past 18 months, there has been an awakening in the United States to the future impact of HDTV, with a resulting shift in the earlier U.S position. Recent U.S. interest has centered on emission standards, and particularly on compatible emission standards.

Previously, U.S. efforts were largely driven by the desire to extend the U.S. advantage in global television program production and distribution into the next-generation television systems. This is one area in which the U.S. retains a large trade surplus, with more than $800 million on the plus side of the ledger last year. A global studio standard for HDTV would favor the U.S. production lead, and might even extend it. HDTV is seen by some as creating the basis for a completely new cinema distribution system, with 35mm and 70mm film eventually disappearing, replaced by direct access to encrypted satellite broadcasts of first-run cinema productions by HDTV projection theatres.

The nature of television broadcasting is very different in the United States from much of the rest of the world. Until recently, television broadcasting facilities in Europe and Japan have been largely owned and operated by national governments or national government corporations. The same programs are seen nationwide, with little local participation. This situation naturally leads to the introduction of new television systems such as MAC and HDTV by means of satellite broadcasting. In the United States, the situation is completely different, with hundreds of locally-owned and operated television stations. Canada and Japan also have significant numbers of local televison broadcasters, in addition to national services. The situation is further complicated in the United States by a lack of available spectrum for new television services in most of the major population areas.

U.S. broadcasters see the necessity to maintain present NTSC transmitters for many years to come, while HDTV services are phased in. During the transition from monochrome to color television, the problem was ingeniously solved by developing a color svstem that could be received on existing monochrome receivers without causing unacceptable degradation, and which operated without requirement for large amounts of additional bandwidth.

The same idea has now been proposed by the FCC as forming the basis for U.S. policy in introducing HDTV or other advanced television services. (Improved systems such as MAC are not precluded.) Recent U.S. efforts have therefore turned away from the studio standard to developing compatible emission systems. (See definition above of compatible systems.) A number of innovative proposals have recently come from the United States, and intensive work is underway in many places.

The bandwidth limitation that has been proposed for terrestrial broadcasting of HDTV in the United States creates a major engineering challenge, as does the requirement for compatibility with existing NTSC signals. It will not be easy to obtain quality that is close to that of the studio signal, including motion portrayal, while maintaining compatibility with NTSC, within the limited additional bandwidth that will be available. (Retaining HDTV resolution for moving objects is especially critical for sports activities. A football game in HDTV is breathtaking). Nevertheless, broadcasters must succeed if they are to remain competitive with other delivery media, which may have full studio-bandwidth signals available.

With the shift in interest from program production (software) to the delivery system (hardware), the approach has dramatically shifted. The reasons for the high level of economically-driven political interest are obvious. Europe alone has about 1.5 times as many television receivers as the United States, all of which will have to be replaced to obtain the benefits of HDTV.

Studio Standards

One of the major achievements of the CCIR during this decade has been the preparation and adoption, in 1982, of Recommendation 601, which provides an extensible family of digital coding standards for television studio signals, up to the point of emission. The CCIR digital coding standard provides for applications ranging from high-definition television to more-compressed electronic news gathering services. The component digital signal is used in all operations from source to transmitter. In 1986, related Recommendation 656 concerning studio interfaces for the digital video signal, and Recommendation 657 dealing with digital television tape recording, were adopted.

CCIR studies on studio standards for high-definition television began as early as 1974, and have been especially intense since 1982. In 1985 a proposed world standard was considered based on 2:1 interlaced scanning with 1125 lines and a field rate of 60.00 Hz. An aspect ratio of 16:9 was proposed, requiring 1920 luminance samples per active line, and 960 color difference samples. A quest for greater compatibility with 50 Hz systems and awakening commercial interest in HDTV in different regions of the world led to an alternative proposal in 1987 for a system using 1250 lines, 50 Hz progressive scanning. The contention mainly involves field rate.

Rapid developments in digital techniques, coupled with falling costs, will allow complex image analysis and processing in the studio and complementary synthesis in the receiver, together with efficient means of long-distance transmission and broadcasting. The historical interdependence of studio and receiver scanning standards will ultimately disappear.
Digital equipment is beginning to appear as islands in various parts of existing broadcasting chains, much of which is in accordance with the requirements of Recommendation 601.

Related to this, intensive work carried out by CCIR study group 11 since the XVIth CCIR plenary assembly (Dubrovnik, 1986) led to the adoption by the extraordinary meeting of draft report XE/11, Future Development of HDTV. The present direction of the CCIR work is established in that report: "The long-term future of high definition television lies in the digital domain and, equally, the long-term future of HDTV's standards should lie with unique worldwide standards."

As happened in the 1940s and 1950s, decisions taken now will shape the future of television for decades into the future. The 21st Century will be the digital century of electronics, so the work of CCIR study group 11 aimed at a digital approach to HDTV is presently receiving considerable emphasis.

The Digital Studio Domain

The following approaches to a unique worldwide studio standard for HDTV in the digital domain were identified at the 1989 CCIR extraordinary meeting of study group 11:

Unique parameter set. All administrations have stated their preference for a sing1e worldwide studio standard for HDTV. A sing1e digital studio standard could be based on 50 Hz, 60 Hz, or even some other value, depending upon such technical factors as motion portrayal and display technology.

Common image/common data rate approaches. Approaches based on common image formats or common data rate are receiving considerable attention, as they could lead to a universally acceptable alternative means of providing HDTV program sources should the attainment of a unique standard prove to be impossible until direct digital distribution of HDTV is established.

Common image (unified) approach. This approach is based on the definition of a common image that can be used in systems that have different frame rates or even different scanning methods. The common elements include aspect ratio, number of active lines, number of pixels per active line, colorimetry and transfer characteristics.

Common data rate (dual-standard) approach. HDTV standards related to current emission standards would be adopted with a maximum of commonality in other parameters such as line frequency and sampling frequency, based on the principls of CCIR Recommendation 601, with the objective of a common data rate. Proposals have been made to the CCIR for systems based on 50 Hz and 59.95 Hz field rates as well as for systems based on 50 Hz and 60 Hz.

Virtual studio standard. A virtual studio standard may be used as a common standard for exchanging programs. A digital data bus with a unique format is used to transport and record HDTV signals. Source and destination could be connected to the unified standard by means of gateways, which perform necessary standards conversions.

Two-step approach. This assumes previous wide-spread introduction of switchable 50 Hz/60 Hz-based HDTV studio equipment. This would not avoid the need for standards conversion in HDTV program exchange between users who have equipment with different standards, but it would allow for the eventual universal use of one or another system.

Delivery Means

In the 1950s, when the CCIR was considering monochrome standards, and again in the 1960s, when color standards were at the center of attention, all efforts were focused on delivery by means of terrestrial VHF or UHF broadcasting transmitters. By the time color standards were adopted, a few cable systems existed, principally to intercept and distribute programs from broadcasting transmitters to viewers in remote or poor-signal areas.

In the 1980s, the delivery situation has changed considerably. Three major new technologies have siphoned off large numbers of viewers from local terrestrial broadcasters: cable distribution, satellite distribution (either via direct reception or in conjunction with cable distribution) and videocassette (VCR) systems.

As a consequence, there is a very real possibility that the next generation television system will be introduced by means of cable systems or recording media, along with terrestrial broadcasting facilities. Broadcasters have recognized this possibility and are responding by establishing and participating in joint efforts to develop and introduce appropriate HDTV systems for production and, particularly, terrestrial emission.

Satellite emission means are particularly attractive to provide the wide bandwidths required for HDTV. Home-market videocassette recorders are in an advanced state of development, and even more significant is the progress towards a read-write optical disk recorder, which could revolutionize television signal recording. Optical fibers have the capability to deliver multi-channel HDTV. The implications of these developments are considerable.

Recording Media

Developments in videocassette and optical disk recording techniques could provide the means for initial introduction of HDTV. In the event of success in this area, terrestrial broadcasters would find themselves at considerable disadvantage. It is not reasonable, however, to make a direct comparison with the introduction and success of PAL/SECAM/NTSC videocassette technology, where the additional moderate cost was limited to the VCR unit and did not require a new video display unit and sound system.

Satellite Direct Broadcasting

In general, television broadcasting in the broadcasting-satellite service (BSS) has gotten off to a slow start, and the presently-planned 12 GHz band was configured for conventional television systems. Nevertheless, satellite broadcasting offers the possibility for the wider bandwidths required for HDTV and coverage of large geographic areas can be achieved very quickly. Satellite broadcasting therefore remains a leading candidate for the initial introduction of HDTV, either by existing broadcasters or by new entities. One country (Japan) has already decided to start regular satellite broadcasting of HDTV, in 1990, following experimental broadcasts of the Korean Olympics in 1988. These services are to be provided by NHK (the national broadcasting organization) and the Japan Satellite Broadcasting Company.

Satellite and Cable Distribution

The distribution, principally to cable systems, of television programming using satellites operating in the fixed-satellite service (FSS) has been enormously successful, particularly in North America, Europe, the USSR and Australasia. Conventional channeling bandwidths offer an impediment to the introduction of wide-RF band HDTV, but techniques are under development to use more than one channel to deliver the signal. The same bandwidth-compression techniques used for HDTV in BSS channels can be applied.

The intended use of FSS television distribution is to feed signals from central broadcasting sources to terrestrial transmitters or cable systems for rebroadcast or distribution to the viewers, but low-noise receivers have made the dircct reception of FSS television signals economically feasible where regulations permit, so FSS direct reception becomes another candidate for the introduction of HDTV in those areas.

The bandwidth of existing cable systems is inadequate for wideband HDTV but a number of bandwidth-compression and multi-channel techniques have been proposed to enable such systems to deliver HDTV signals. Cable systems are therefore also candidates for the initial introduction of HDTV, but with many of the same bandwidth limitation problems in existing systems as terrestrial broadcasting. New broadband cable systems do not have
comparable bandwidth limitations.

The Broadband ISDN

In some countries, sound broadcasting programs have been delivered to homes as a value-added service of the public telephone network for many years. A parallel development may come to television with the advent of the broadband integrated services digital network (B-ISDN). Work towards standardization of the broadband ISDN is at an advanced stage in the CCITT, and PTTs and telephone operating companies in many areas are making plans for the introduction of broadband ISDN services during the next decade. Depending upon political decisions in many countries, television, including HDTV, will likely be an essential element of such networks, if the cost of installing wide-band fiber optic subscriber loops is to be justified.

Terrestrial Broadcasters

Terrestrial broadcasters face the greatest technical difficulties in introducing HDTV. Assuming that broadcasting a suitably-compressed HDTV signal requires from 1.5 to two times greater bandwidth than broadcasting a PAL, SECAM or NTSC signal, terrestrial broadcasters have to find additional channels while maintaining conventional emissions. In many countries, where the broadcasting spectrum is already heavily occupied and where there is also tremendous demand for VHF and UHF spectrum for rapidly-expanding mobile services, it may simply be impossible to make large amounts of additional broadcasting spectrum available. Techniques such as the alternate use of horizontal and vertical polarization in adjacent service areas offer the possibility for significant improvements in spectrum occupancy for television, albeit at some cost, both to broadcasters and to viewers, but could result in considerable inconvenience to the viewing public if implemented.

Emission Standards: Satellite Broadcasting

CCIR studies on emission standards for satellite broadcasting began in earnest in 1986, following the adoption by WARC-ORB 85 of Recommendation 3 on high definition television in the broadcasting satellite service, which invited the CCIR to undertake specific studies and to report on the result of its work to the second session of the conference (Geneva, 1988).

A comprehensive report on the subject was approved by the 1987 joint interim meetings of CCIR study groups 10 and 11. The direction of the CCIR work in this area is summarized in these extracts from the CCIR report to WARC-ORB. The problem of finding the right balance between the conflicting parameters of picture quality, receiver complexity, number of programs available, and total bandwidth needed has no unique solution. The CCIR made efforts to show clearly the relationship between the factors involved and to indicate advantages and disadvantages of the possible choices.

The studies have led to the following conclusions:
1. Both analog and digital systems are feasible.
2. All systems need a certain amount of bandwidth compression.
3. Narrow RF-band systems (operating in a 24-27 MHz channel) are characterized by relatively high degrees of bandwidth compression and by analog modulation.
4. Wide RF-band systems (both analog and digital) require an RF channel bandwidth typically on the order of 50 to 120 MHz.
5. The degree to which HDTV transmissions can be used depends upon the particular plan in each region. However the 12 GHz band as planned will not accommodate single wide-RF channel analog or digital HDTV signals on a worldwide basis.
6. From a propagation point of view all bands from 12 GHz to 23 GHz may be suitable.
7. There is already significant utilization of many of the frequency bands which might otherwise be suitable.
8. The general conclusion is that broadcasting of HDTV should provide the potential of a picture quality which comes as close as possible to that of the studio signal for reception in homes.

The WARC-ORB 88 took into account the work of the CCIR and recommended to the plenipotentiary conference of the ITU (Nice, May/June 1989) to include provision in the post-1989 program of conferences and meeting for a world administrative radio conference competent to deal, inter alia, with frequency allocation for HDTV. The Nice plenipotentiary conference included this activity in a limited-allocation World Administrative Radio Conference that will take place in Spain during the first quarter of 1992.

The administrative council of the ITU was asked to ensure that the agenda of the conference authorizes it to:
1. Make the definitive selection of, and the appropriate radio regulatory provisions for, a frequency band for HDTV in the broadcasting-satellite service in the long term and for an associated HDTV feeder-link band, both preferably on a world-wide basis.
2. Adopt appropriate provisions to regulate the sharing of any such bands with other radiocommunication services, being guided by the appropriate CCIR studies, taking into account the needs of any existing services which might perhaps have to be adjusted or re-accommodated elsewhere in the frequency spectrum, including the time required to effect any necessary changes.
3. Determine the dates for the entry into force of its decisions, including the earliest date for the introduction of HDTV and associated feeder links into any frequency bands selected for these purposes.

The necessary further studies to support the technical decisions of the proposed conference are in progress in the CCIR. In countries where broadcasting is mainly carried out on a national basis and where there are few local television broadcasters, satellite emission seems especially promising for the introduction of HDTV.

Emission Standards: Terrestrial Broadcasting

The extraordinary meeting of CCIR study group 11 on high definition television addressed the question of the terrestrial broadcasting of HDTV. Three strategies were considered:
1. Introduction of HDTV via existing conventional scanning formats.
2. Direct introduction of HDTV via a non-compatible scanning format.
3. Introduction of HDTV via agile conventional receivers.

Since the terrestrial emission of HDTV is an area that began to receive concentrated attention on a widespread basis in the CCIR only two years ago, the numerous studies and research activities in progress result in a constantly-changing situation. Several systems under development are described in CCIR Report 801-3.

HD-MAC has been proposed in Europe for satellite, cable and terrestrial distribution and is the subject of current studies with different system proposals for AM/VSB and FM emission or transmission.

Japan will begin regular satellite broadcasting of HDTV in 1990 using a member of the MUSE family of HDTV emission formats, which employs an 1125/60 2:1 video signal. Several variants of MUSE, with varying amounts of video signal compression and processing, have been developed for satellite, terrestrial and cable emission or transmission. Considerable work is in progress in the United States and Canada.

The CCIR Extraordinary Meeting

The XVIth plenary assembly of the CCIR (Dubrovnik, 1986) decided to schedule an extraordinary meeting of CCIR study group 11 devoted exclusively to high definition television to develop appropriate HDTV studio, emission and transmission standards.

Senior technical and policy representatives of HDTV development activities from around the world attended this meeting, held in Geneva in May, 1989. This extraordinary meeting was the first global forum where all aspects of HDTV were examined in detail. Coordination of standardization activities of the international organizations involved in HDTV development was emphasized, particularly among those concerned with information technology such as the CCITT, the IEC and the ISO, whose observers participated in the meeting.

The global approach of CCIR study group 11 is oriented towards determining the role of HDTV in the information society of the 21st Century, and includes the harmonization of standards and operating practices for HDTV production, emission and transmission, as well as for non-broadcast HDTV equipment intended for consumer applications.

The extraordinary meeting of CCIR study group 11 made considerable progress towards the long-stated goal of a world-wide HDTV studio standard. Four draft new recommendations were prepared, including basic parameter values for the HDTV studio standard and international program exchange, subjective assessment methods for image quality in HDTV, recording of HDTV images on film and international exchange of programs electronically produced by means of HDTV.

CCIR Report 801, The present state of high-definition television, was completely rewritten and serves as a veritable compendium of state-of-the art information on global work in progress in the field. Eight other CCIR reports, covering the details of every aspect of the development and utilization of HDTV, were prepared or revised.

The conclusions of the meeting state that a unique studio standard is a clearly identified need and must continue to be the main target. All participants in study group 11 were invited to carry on with tests and experiments (including comparison tests) in order to achieve this goal. More up-to-date information will be prepared by study group 11 for the CCIR XVIIth plenary assembly, which will take place in Dusseldorf in May, 1990. Since all the studies on HDTV may not be completed, the study of some parameters may continue, but there was general agreement to specify most of them before that date.

The study group identified the necessity to adequately take into account the increasing1y strong relationship between broadcast and nonbroadcast activities, and particularly their equipment and specifications, mainly with respect to consumer and telecommunication applications. CCITT study groups dealing with the broadband integrated services digital network (ISDN), the ISO and the IEC are principally involved.

The conclusions further state that, from experience and operational considerations, the interrelationships between each part of the HDTV network (from production, through contribution and distribution to emission) have to be taken into account in an overall evaluation of the complete HDTV system. Furthermore, it is necessary to form a view of how the new HDTV system would be implemented. This should bear in mind already existing arrangements for conventional television, and the operational and economic benefits or penalties that might arise under different studio, transmission and emission standards. Study group 11 also observed that the evolution of suitable display devices for the home receiver still requires considerable effort.

Where Do We Go From Here?

Impact. Before proceeding further, it is essential to examine the global implications of the development of the HDTV system of the 21st Century. Foremost is the financial impact. We are talking about a multibillion dollar market in new equipment receivers, studios, recording and transmission equipment and in program production. There is the additional multi-billion dollar existing investment in conventional systems which has to be amortized over a reasonable life cycle.

Therefore, decisions on new standards must be taken only after thorough examination of the consequences in the global environment. The advent of HDTV in each country will depend upon the configuration of broadcasting and its infrastructure as well as the level of economic development, hence the impact for any particular country will depend upon when and how HDTV is introduced.

One system or many? In examining the diverse requirements and limitations of: source and production media; the various delivery media (cassette/optical disk recorders, satellites, cables, terrestrial transmitters); and viewers and other users (individuals, cinemas, businesses), it seems unlikely that a single emission standard, either in terms of quality or technical parameters, could be developed for economical use in all applications. On the other hand, a single worldwide family of standards should be achievable, if the study group 11 approach to a unified worldwide digital HDTV studio standard is followed.

Broadcasters and production organizations would especially benefit from a single worldwide production standard, just as viewers and receiver manufacturers would benefit from a single worldwide emission standard, which would ideally use a baseband signal as closely-related to the production standard as possible.

Receiver cost is of great importance to the consumer and may adversely affect willingness to embrace HDTV if it is too high. If there were otherwise no trade barriers, all receiver manufacturers would have a global market available and because of the economies of scale that result from large production runs, receivers built to conform to a single worldwide emission standard family should be more economical to produce, and therefore of lower cost to the purchaser, than receivers built to conform to one of two or more regional standards, provided each of the regional standards is designed to produce roughly equivalent quality.

A major change that has occurred in the past 20 years is the disappearance of protected markets for television receivers. This has been due partly to liberalization of trade polices, and partly to changes in technology. Competing manufacturers now have the capabilities to design and market products compatible with virtually any standard, in any market, at a competitive price and in a very short time after a new product is introduced.

The following quotation from the July 1988 issue of the HDTV Newsletter illustrates this point. "Dr. Irwin Dorros, president of Bell Labs, says that the biggest misconception of the HDTV issue is that the choice of the standard will make any difference whatsoever in who supplies the equipment. He also notes that the main thing to keep in mind is the public outcome. It is not a matter of who will most benefit from patents. It is a matter of what serves the public best."

Time frame. Time frame is the critical element in deciding upon a standardization approach. There are several factors that will preclude rapid introduction of HDTV on a large-scale basis, whatever the medium. First, and not the least important by any means, is the size, weight and power consumption of suitable large-screen displays. Next is the cost to the viewer, not only of the large-screen display, but also of the associated tuner, processing electronics, sound system and VCR or optical recorder. A lightweight, affordable large-screen HDTV system is not yet on the horizon.

Because of these factors, the introduction and popularization of HDTV is much more likely to follow the model of color TV than that of CDs. Recall that more than ten years elapsed from the introduction of large-scale color emissions until widespread public acceptance (as evidenced by receiver purchases). And this took place in an environment of compatibility with existing monochrome systems with ample programming available. Even the build-up in popularity of VCRs was spread over several years. The rapid success of the compact audio disk is not analogous, as it benefited not only from a remarkable improvement in quality, but was an add-on to existing systems at relatively small additional cost.

With ten or more years available to perfect and introduce suitable emission and transmission systems for HDTV, the approach of study group 11, as summarized above, could lead to reasonable standardization of emission systems that would truly be matched to 21st Century requirements. In addition, existing investments could be fully protected and utilized, while future investments could be optimized and spread over a reasonable time.

Current Developments

Broadcasters have mounted a major campaign in the United States to develop a compatible HDTV system, and cable system operators are becoming increasingly concerned about the potential threat of competition from the wide-band ISDN. These efforts and concerns, when coupled with the development of a number of variations of the Japanese MUSE emission system, the European Eureka-95 project and a number of on-going development efforts in the United States and Canada may well lead to conclusion of the CCIR standardization effort within the next study cycle.

Richard Nickelson is a senior counsellor and head of the technical department dealing with the broadcasting-related study groups of the CCIR, including the broadcasting-satellite service. He holds BEE and MS degrees in electrical engineering from the Georgia Institute of Technology. Mr. Nickelson has been a satellite communications system engineer since 1963, and has been involved in a number of experimental satellite programs. He was a member of the staff of Lincoln Laboratory, MIT, from 1967 to 1971, and participated in the joint design study for the Indian National Satellite which was conducted by MIT and the Indian Space Research Organization. He joined ITU in 1971 as technical coordinator for the Satellite Instructional Television Experiment in Ahmedabad, India. In 1976 he was transferred to Geneva, where he worked as a project officer in the ITU technical cooperation department. In 1980 he became study manager for the ITU project on development of rural telecommunications in Africa, and in 1981 he was appointed to his present position. Mr. Nickelson is a member of the IEEE Communication Society.