Image formats for HDTV

Find out why there is little justification for European broadcasters to introduce new production formats for HDTV
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For several years, European broadcasters have been making programs in high definition — often based upon co-production deals with the USA and Japan — using the 1920×1080 Common Image Format. However, European consumers remain restricted to down-converted SD versions of the original full-resolution HD content. This situation will soon change as more broadcasters offer HD services and viewers turn to satellite services like Euro1080 for their HD content.

And now HD

HD has been with us since the early 1990s, but those early European attempts unfortunately proved unsuccessful. So what has changed?

The renewed interest can be attributed to several factors, the main ones being: the availability of high-resolution, large, flat-panel displays; a track record of success in other parts of the world; and desktop high-definition production and editing — all of these at significantly reduced costs.

High definition, as we know it today, has always been a widescreen 16:9 (1.78:1) format, not quite going to the extremes of the film industry with ratios of 1.85:1 up to 2.35:1, but a reasonable compromise between the needs of television and movies.

Looking at the current worldwide situation (see Figure 1) and the USA in particular (see Figure 2 on page 38), HD can be characterized from a consumer perspective in terms of spatial resolution as follows:

  • Image format: 1920×1080 with a minimum of 1280×720.
  • Flat-panel display format: 1920×1080 with a minimum of 1440×768.


Euro1080 broadcast in high definition the Vienna New Year’s Day concert, which included a performance of the Vienna State Opera Ballet shown here.

Figures 1 and 2 provide an overview of the picture format decisions already in place. As can be seen from these illustrations, Asia, North America and Australia have chosen to produce programs and broadcast using 1080i. In the USA, where 1080i is the dominant format, ABC, ESPN and FOX are transmitting 720/60p, trading off the lower static resolution for improved motion portrayal.

The worldwide situation is, of course, of significance to Europe because, as a “late-comer”, it is highly preferable that one or more of these formats should be selected, rather than inventing yet another variant. Inventing a new picture format at this late stage would not be welcomed by manufacturers or end users.

In production, three image formats currently predominate:

  • 1920×1080×60/50i
  • 1920×1080×24/25/30p
  • 1280×720×60p

Note that for simplicity, 60 in this article represents both 59.94Hz and 60Hz.


Figure 1. Worldwide HD broadcasting. Click here to see an enlarged diagram.

The introduction of the 1920×1080 picture format represented an industry breakthrough when it was recognized and accepted by the ITU as the worldwide Common Image Format. For the first time in television history, an image format exists that is accepted by all parts of the world for both television and film use. Although technically more demanding, it is inevitable that 1920×1080×50p will be added to the production format line-up as it combines the benefit of high resolution with superior movement portrayal. This is particularly important in production, where the quality requirements are at their highest.

When the three-dimensional spectrum limits of 1920×1080×50P are observed (see Figure 3), it can be seen that all the other formats are a subset. The picture quality of down-sampled 1080/50p exceeds that achieved using native acquisition for each individual format — in much the same way that 35mm film material, when converted to standard definition, looks outstanding with many of the annoying alias components removed by the down-sampling and filtering process.

It should be said, however, that the film industry intends to go further by offering an even higher resolution 4K picture format for movie production. Even so, 1920×1080 is the closest to a universal scanning format that exists. It would have been even better if commonality could have extended to the frame and field rates but, for the moment, the 50/60Hz divide still remains.


Figure 2. HDTV broadcasters in the USA. Click here to see an enlarged diagram.

One might ask: “Why these particular parameters?” Apart from the usual anomalies of a politically-driven decision that is acceptable to all parties, some specific and useful simple sample ratios are recognizable. For example, if the standard-definition 4:3 horizontal pixel count of 720 is reworked for 16:9 and, at the same time, the resolution is doubled, the following relationships can be observed:

1920×1080×60/50i

  • 720×3/4×16/9×2 = 1920 pixels/line.
  • 1920×9/16 = 1080 lines (based on square pixels).

Originally, interlace was perceived as a method corresponding to the scanning limitations of CRT tubes. More relevant today are the interlace benefits of high spatial resolution at reduced data rates when compared to the equivalent progressive scan. The price paid for this is a slight softening and increase of alias components for high-resolution moving images to which, fortunately, the human eye is psycho-visually not sensitive.

One of the most remarkable changes about HD is the way in which drama and television series production has evolved in the USA. While the USA is a well-known exporter of movies, it also exports many of its soap opera programs (soaps) worldwide.


Figure 3. Four image formats — spectral limits relative to 1920x1080x50p, Click here to see an enlarged diagram.

The majority of the high-value soaps were originally shot on 35mm film and subsequently converted to the target television standards. For a series that needs to produce a large volume of program material in a short period of time, the use of film is time-consuming, expensive and inconvenient. It should, therefore, come as no surprise that many of these programs are now shot in the film-friendly rate of 24p in HD. Cheaper recording media and instant playback are immediate tangible benefits.

1920×1080×24/25/30p

Figure 4 shows examples of programs shot and broadcast in HD by the major U.S. networks. Material produced in this way can be conveniently converted for worldwide distribution and can also be converted to other formats for transmission.

If we assume that 1920×1080×24p represents a universal solution, then retaining a certain commonality with film production and also offering convenient transfers to all worldwide high-definition and standard-definition formats is possible. This format is not, however, popular for sports, where the slow frame rate “film look” is not well appreciated and for which 50/60i or 50/60p offer better movement portrayal.

In the USA, ABC, ESPN and FOX transmit in 720/60p, even though some of their productions are also 1080-based. 720/60p is recognized also by the ITU — but not 720/50p. It can be argued that at a time when displays are often 480 and 768 line-based, the benefit of a higher transmission resolution is reduced. As previously described, however, downsampling from a higher resolution still produces superior pictures. Given the current status of display technology, the choice of 720p by networks focusing on sports like ESPN, ABC and FOX is understandable.

However, there are some new considerations on the horizon. All the major flat-panel screen manufacturers have announced that the next generation of television displays will follow the 1920×1080 Common Image Format. This is the first time that screen sizes are to be video-centric rather than computer-centric. It represents the recognition by manufacturers that 1920×1080 will be the “sweet-spot” and the mass market of the future. With HD format decisions preferably remaining valid for the next 30 years or more, it becomes clear that significantly larger screens and higher resolution will become commonplace.


Figure 4: Production formats for the above programs. Click here to see an enlarged diagram.

In January 2004, high-definition broadcasting was launched in Europe with the introduction of Euro1080. As the name implies, the transmission format is 1920×1080i using MPEG-2 compression. The transmission is handled by an Astra satellite and covers most of Europe.

1280×720×60p

The parameters chosen for satellite transmission, and indeed for other transmissions around the world, expose an acute problem facing all terrestrial broadcasters; a lack of bandwidth. Most satellite services have access to 15Mb/s or more for transmission. However, because of the European digital multiplex structure, terrestrial broadcasters must fit HD services within an 8Mb/s to 10Mb/s data rate. Therefore, every possible method of reducing the data rate is under study, including new compression schemes such as AVC and H.264. Because these services are dependent on new technologies and the available spectrum, it is unlikely that HD terrestrial transmissions will take off before 2008.

The future

In contrast, satellite HD services have been announced by private broadcasters in the UK, France and Germany with a 2005-2006 time-frame, just ahead of the 2006 football World Cup 1. The wider bandwidth of satellite delivery will allow these private broadcasters more freedom to select the transmission format and use 1080i with MPEG-2 or AVC/H.264.

Broadcast delivery options for Europe

There are many other consumer and entertainment options that will help expand the market and make HD more commercially attractive. A selection of these applications include:

  • Movie production.
  • Digital cinema: movie distribution and exhibition.
  • High-definition DVDs for packaged media and recording.
  • Internet streaming and distribution.
  • High-resolution video games consoles.
  • Consumer home-movie making.
  • Medical applications.
  • Military and surveillance.

Perhaps the advent of digital projection will mark many Europeans' first exposure to HD video images. The installation of digital projectors in movie theaters continues to grow, and distribution networks are gradually being established. Euro1080 has built a network of cinemas for its “Events” channel, showing live sporting events and concerts.

High-definition formats for non-broadcast applications

Theater projectors have until recently been restricted to 1280×1024 but are now becoming available with a full resolution of 1920×1080, and even 4k projectors have been demonstrated as prototypes.

European broadcasters have been making programs in HD for several years using the 1920×1080 Common Image Format. The result is a rapidly growing library of programs in countries that have pushed ahead with HD transmission. Unfortunately, European consumers are currently restricted to downconverted standard-definition versions and are denied access to the original full-resolution HD content.

This situation will soon change as more broadcasters begin offering HD programming and new satellite services like Euro 1080 begin transmission in HD.

It is this author's opinion that all these factors combine to mean there is little justification for adopting production formats other than those already in extensive use around the world today — predominantly 1080i, with the exception of those networks focused on sports programming like ABC, ESPN and FOX.

What to do now

Adopting different standards would just position Europe as a minority player and make international program exchange unnecessarily more complex.

The technology is available now, and consumer HD awareness is increasing. It really does look as if the false start of the early 1990s can be put behind us, so broadcasters should ready themselves to implement HD sooner rather than later.

John Ive is director of strategic planning for Sony Europe.