World Television Standards and HDTV/DTV

Although the total number has diminished somewhat, there are still several incompatible broadcast television standards (technical approaches to broadcasting the picture and sound) in the world. This means that a program produced in one country can't be automatically viewed in another country without converting it to the appropriate technical standard.

Since film and television programming represents one of the largest and most lucrative exports for the United States--by some figures the number one export--television producers and syndicators in the US need to be familiar with the differences in world television systems. Many film and TV productions do not even start to make money until they go into foreign distribution.

There have been about 14 different broadcast standards in use at different times throughout the world. Today, excluding DTV (digital TV) three basic systems serve the vast majority of countries (although there are some significant variations within these).

NTSC (National Television System Committee)
SECAM (Sequential Color And Memory)
PAL (Phase Alternating Line)

We'll discuss each of these in more detail later in this module.

The difference between these basic international broadcast standards centers primarily on four things:

the number of horizontal lines in the picture (525 or 625)
whether 30 or 25 frames (complete pictures) are transmitted per second
the broadcast channel width (electronic bandwidth of the signal)
whether an AM- or FM-type signal is used for the audio and video

Historically, the number of lines used in broadcast TV has ranged from the United Kingdom's 405-line monochrome system to the 819-line system used in France. Both of these systems have now been phased out. So, excluding digital and high definition systems to be discussed later, the world has been left with two basic line standards: 525 and 625.

Aspect Ratios

Although the number of scanning lines may have varied, all of television systems had the same 4:3 aspect ratio. The aspect ratio is the width-height proportion of the picture.

The 4:3 ratio was consistent with motion pictures that predated the wide screen aspect ratios used in CinemaScope, Vista-Vision and Panavision films. As we will see, HDTV uses a 16:9 aspect ratio (roughly, the larger area in the parrot picture).

The most commonly used wide-screen movie format is slightly larger than 16:9 (although the difference is insignificant). However, at 2.35:1 the CinemaScope aspect ratio is considerably wider than 16:9.

The NTSC Broadcast Standard

The National Television Systems Committee's (NTSC) 525 line, 30 frames per second system is shared primarily by the United States, Canada, Greenland, Mexico, Cuba, Panama, Japan, the Philippines, Puerto Rico and most of South America.

The NTSC standard was first developed for black and white (monochrome) television in 1941. In 1955, the color standard was established.

The NTSC system of television is referred to as a 525 line, 60 field system because, as we'll see, the 30 frames consist of 60 fields.

The NTSC's 60 field system originally based its timing cycle on the 60 Hz (cycle) electrical system used in these countries. Since other countries in the world use a 50 Hz electrical system, it was logical for them to develop systems of television based on 50 fields per second.

The basic NTSC standard is almost 50 years old and many technical improvements have come about in that time. Although the NTSC standard has served us well, the new digital standards take advantage of many new technical capabilities and will provide major improvements over the NTSC standard.

The PAL and SECAM Television Systems

More than half of the countries in the world use one of two 625 line, 25 frame systems: the SECAM (Sequential Color And Memory) or the PAL (Phase Alternating Line) system.

SECAM was developed in France and is used in parts of Europe, including countries in and around the old Soviet Union.

PAL was developed in Germany and is used in Britain and most of Western Europe, except for France.

The extra 100 lines in the SECAM and PAL systems add significant detail and clarity to the video picture, but the 50 fields per second (compared to 60 fields in the NTSC system) means that a slight flicker can sometimes be noticed.

Even so, since 25 frames per second is very close to the international film standard of 24 frames per second, film is more easily converted to the PAL and SECAM video systems.

With NTSC television things are more difficult; the 24 frame-per-second film rate must be converted to 30 frames-per-second. This is done by scanning film frames twice at regular intervals--a bit of an awkward procedure, but it works.

Standards Conversion

The presence of different broadcast TV standards means that the exchange of international programming is made more difficult. Videotape made in the US cannot be played in England, for example, without going through electronic standards conversion.

This used to be a major problem. But with today's digital technology the process of converting from one international standard to another is rather simple, quick and painless (assuming you can afford the cost of professional equipment). ntscpal.gif (6472 bytes)

Standards conversion centers on changing the 60 fields per second (NTSC system) to the 50 fields per second ( PAL and SECAM systems) and vise versa. As shown at the right, the solution is either to repeat or skip fields at regular intervals.

Today, there are also multi-standard TV sets and VCRs available that switch from one standard to another. As we move into the new digital systems, converter boxes will become available to translate these standards into whatever standard your set can display.

Digital and High-Definition Television

In early 1998 the Federal Communications Commission (FCC) in the United States issued a long-awaited decision on future possibilities for television. The future is all digital (DTV), and within this all digital future more than 30 possible standards exist. Some of these are referred to as HDTV (although what is and what isn't high-definition is often debated).

If you want a more detailed look at the various DTV standards and the preliminary network decisions, click here.

Before long, standards converter boxes will be available to translate any of the standards being broadcast into the one most acceptable for your TV set. If, for example, you tune into a station broadcasting an HDTV signal and your TV set is still a 525-line analog set, the converter box will change the HDTV signal into one that can be used by your TV set. Although you will lose the full quality of the HDTV signal, the converted signal should still be better than today's standard NTSC signal.

The first all-digital station, KITV in Hawaii, went on the air in January, 1998. It broadcast digital programming along with its standard Channel 4 analog signal. Even though there were virtually no digital TV sets to receive the signal, the public relations value in being first put KITV "on the map" (including receiving a "broadcaster of the year" award) and it has put pressure on competitors in the market to also move to digital.

By the latter part of 1998, a number of US TV stations were broadcasting digital signals, including HDTV. Even so, the number of digital receivers is still limited.

Most of the impetus for going digital will come from the networks. Once the networks start high-definition/digital programming, the signals from the local stations (affiliates) will look inferior in comparison. Advertisers (who ultimately drive the system) will quickly notice that their locally-produced commercials look inferior to the network programming, and will push the stations to upgrade.

All 1,600+ TV stations in the United States have been assigned new digital frequencies by the FCC. For example, Channel 2 in Los Angeles has been assigned channel 60, which means it will jump from one of the lowest frequencies to one of the highest.

Although the digital signal will experience less interference than the channel 2 analog signal, because of the much higher frequency it will take nearly one million watts of power to reach roughly the same coverage area. Electric bills for this level of power can run to $30,000 a month.

Even with this huge increase in power and a transmitting antenna height of more than 1,000 meters there is some question whether they will be able to reach the same area as their existing channel 2 signal. This concern is also shared by some of the other stations who have recently been given DTV channel assignments by the FCC.

Once the analog-to-digital transition period is over (which will take at least ten years), the analog transmitters will be shut down and those frequencies will be released for use by other applications--some of which we haven't even dreamed up yet.

With the final cost of making the move to DTV in the United States running into the billions of dollars, the question arises, how will some of this money be recouped?

The new digital schemes allow for a variety of additional services to be broadcast along with the new digital signal. Options include pay-per-view movies, high-speed Internet services and additional TV channels--all within the same digital broadcast channel.

Other countries have their own schedule for the move to DTV and HDTV. But, because their governing bodies have typically allowed fewer options, there will probably be less confusion over standards.

Fortunately, the digital standards selected by most countries are basically compatible, even though they may be based on a 50-Hz electrical standard rather than the 60-Hz one used in the United States and some other countries.

Since digital electronics is involved, conversions from one country's digital standard to another will be simpler than it has been with analog technology.

Compared to standard NTSC television, HDTV is able to reproduce six times the detail and ten times the color information.

Compare the enlargements shown here representing HDTV and the standard NTSC systems. (Note: When you move back from the screen to a distance approximating normal TV viewing distances, the differences between these photos are not nearly as obvious.)

When projected on a 16- by 9-foot screen and observed from a normal viewing distance, the picture detail in HDTV/DTV appears to equal what is normally attained by projected 35mm motion picture film.

Even so, video and film are inherently different media. The question of their relative "quality" (a word which can mean many things to many people) has been a subject of lively debate--and one that can't be decided by purely technical criteria.

Suffice it to say, when the film and video media are compared in a broadcast application, the difference between video and film is based more on the respective production approaches than on any inherent quality differences between the media. More on that later.

Converting Wide-Screen Formats

The conversion of 16:9 HDTV/DTV images to the standard 4:3 aspect ratio is done in basically the same way as the conversion of wide-screen films to NTSC television.

There are three approaches.

First, the sides of the picture can be cut off. If the original HDTV/DTV (or wide-screen film) is shot with the narrower 4:3 cutoff area in mind--a procedure referred to as shoot and protect--losing the information at the sides of the picture may not be a problem.

Second, the entire production can go through a process called pan-and-scan. This involves a technician reviewing every scene and programming a computer-controlled imaging device to electronically pan the 4:3 window back and forth over the larger, wide-screen format.

In the parrot picture cutting off the sides would not be an issue; but, if you had two parrots looking at each other (talking to each other?) from opposite sides of the screen, it would be.

Finally, if the full HDTV/DTV frame contains important visual information (as in the case of written material extending to the edges of the screen) panning-and-scanning will not work. In this case a letterbox approach can be used.

But there is a problem. This results in blank areas at the top and bottom of the frame. Often, letterbox is reserved for the opening titles and closing credits of a production with the remainder of the production being panned-and-scanned.

Since many directors feel that pan-and-scan introduces pans that are artificial and not motivated by the action, they insist on the letterbox conversion approach.

Originally, producers feared that audiences would object to the black areas at the top and bottom of the letterbox frame. (More than one person who rented a film in the letterbox format has brought it back to the video store, complaining that something was wrong with the tape.) However, today the letterbox format is commonly seen and fairly well accepted.

For short segments of a production, there is another way of handling the 16:9 to 4:3 aspect ratio difference. You have probably seen the opening or closing of a film on television horizontally "squeezed" to accommodate the titles and credits. The effect is especially noticeable when people are a part of the scene--people who, as a result, suddenly become rather thin. Compare the two images here. Note how the bird in the 4:3 ratio seems to be thinner.

The narrowing effect is caused by the anamorphic lens used on the film camera that routinely compresses a wide-screen format into the standard 4:3 film ratio.

Normally, of course, when this film is projected in a theater the compressed image is stretched back to its original, wide-screen ratio. But, when used in TV with a 4:3 aspect ratio it's not possible to stretch it back out to its full width.

Before DTV/HDTV becomes the norm in 2003 or so, we'll be worrying about converting all the old 4:3 ratio programming into the wide screen format. Today, even though we haven't moved to HDTV/DTV, many producers are shooting productions in the wide-screen format, just so their product will still be useful in the coming DTV/HDTV era.

World Television Standards and DTV/HDTV

The NTSC Broadcast Standard

The PAL and SECAM Television Systems

Standards Conversion

Digital and High-Definition Television

Converting Wide-Screen Formats