HDTV has been getting media attention for several years now, and if you go to an electronics store you can see a fairly good selection of HDTV sets today. If you have ever looked at one of these sets, you know that the image they display is sharper and wider -- it is more like a movie screen than it is a TV set! HDTV has lifelike pictures and digital sound. The higher resolution produces clarity like you have never seen from a picture tube. Films retain their original width, enhancing your home theater experience. Imagine seeing more of a football field or a scenic panorama!

Helpful books

Guide to HDTV Systems by Conrad Persson

The Guide To Digital Television by Michael Silbergleid, Mark J. Pescatore

Now, we'll take a close look at HDTV and what you get with HDTV. We'll also explain the equipment needed and talk about what you should consider when purchasing a set. There's also a huge link section so that you can learn more!

What Is HDTV?
If you have read the Stuff.dewsoftoverseas.com article entitled
How Television Works, then you know all about what is now called analog TV. In analog TV, a 6 MHz analog signal carries intensity and color information for each scan line of the picture. An analog TV signal in the U.S. has 525 scan lines for the image, and each image is refreshed every 30th of a second (half of the scan lines are painted every 60th of a second in what is called an interlaced display). The horizontal resolution is something like 500 dots for a color set.

This level of resolution was amazing 50 years ago, but today it is rather passe. The lowest resolution computer monitor that anyone uses today has 640 by 480 pixels, and most people use a resolution like 800 by 600 or 1024 by 768. We have grown comfortable with the great clarity and solidity of a computer display, and analog TV technology pales by comparison.

Many of the new satellite systems, as well as DVD disks, use a digital encoding scheme that provides a much clearer picture. In these systems the digital information is converted to the analog format to display it on your analog TV. The image looks great compared to a VHS tape, but if would be twice as good if the conversion to analog didn't happen.

There is now a big push underway to convert all TV sets from analog to digital, so that digital signals drive your TV set directly. Your new digital TV is, basically, a computer monitor. It accepts pure digital signals and provides a high-resolution picture that is extremely crisp and stable.

When you read and hear people talking about Digital Television (DTV), what they are talking about is the transmission of pure digital television signals, along with the reception and display of those signals on a digital TV set. The digital signals might be broadcast over the air or transmitted by a cable or satellite system to your home. In your home, a decoder receives the signal and uses it, in digital form, to directly drive your digital TV set.

There is a class of digital television that is getting a lot of press right now. It is called High Definition Television, or HDTV. HDTV is high-resolution Digital television (DTV) combined with Dolby Digital surround sound (AC-3). HDTV is the highest DTV resolution in the new set of standards. This combination creates a stunning image with stunning sound. HDTV requires new production and transmission equipment at the HDTV stations as well as new equipment for reception by the consumer. The higher resolution picture is the main selling point for HDTV. Imagine 720 or 1080 lines of resolution compared to the 525 lines you are used to in the U.S. (or the 625 lines in Europe) -- it's a huge difference!

Of the eighteen DTV formats, six are HDTV formats—five of which are based on progressive scanning and one using interlaced scanning. Of the remaining formats, eight are SDTV (four wide-screen formats with 16:9 aspect ratios, and four conventional formats with 4:3 aspect ratios), and the remaining four are Video Graphics Array (VGA) formats. Stations are free to choose which formats to broadcast.

The formats used in HDTV:

  • 720p - 1280x720 pixels progressive
  • 1080i - 1920x1080 pixels interlaced

Interlaced or Progressive refers to the scanning system. In an interlaced format, the screen shows every odd line at one scan of the screen, and then follows that up with the even lines in a second scan. Since there are 30 frames shown per second, the screen shows one half of the frame every 1/60 of a second. For smaller screens this is less noticeable. As screens get large the problem with interlacing is flicker. Progressive scanning shows the whole picture, every line in one showing, every 1/60 of a second. This provides for a much smoother picture, but uses slightly more bandwidth.

MPEG-2
Broadcasters are having to squeeze the increased picture detail and higher quality surround sound into the same 6-megahertz bandwidth used by analog television (see How Television Works for details on bandwidth). Compression software, very similar to what is used in personal computing, allows this to happen.

Digital TV relies on a compression and encoding scheme known as MPEG-2 to fit its stunning images into a reasonable amount of bandwidth. In each image, the MPEG-2 software records just enough of the picture without making it look like something is missing. In subsequent frames the software only records changes to the image and leaves the rest of the image as-is from the previous frame. MPEG-2 reduces the amount of data by about 55 to 1. MPEG-2 already is the industry standard for DVD videos and some of the satellite TV broadcast systems. Compression reduces image quality from what is seen by the digital camera at the studio. However, MPEG-2 is very good at throwing away image detail that the human eye ignores anyway. The quality of the image is very good, and significantly better than traditional analog TV.

The use of MPEG-2 permits a HDTV receiver to interact with computer multimedia applications directly. For example, a HDTV show could be recorded on a multimedia computer, and CD-ROM applications could be played on HDTV systems. A Digital TV decodes the MPEG-2 signal and displays it just as a computer monitor does, giving it high resolution and stability.

Are There Any HDTV Stations?
There are
HDTV stations "on the air" in many larger cities. The first HDTV station was WRAL-HD in Raleigh, NC. The Federal Communications Commission (F.C.C.) has mandated that all stations be capable of broadcasting HDTV by 2006. The timeline of HDTV coverage gives you an idea of what will be available in your area, and when. Click here to learn what's on HDTV today.

The FCC mandate affects broadcasters, cable companies and consumers in significant ways:

  • Consumers have to buy new equipment -- either a set-top box (to convert digital signals to analog signals) or a whole new TV set.
  • Broadcasters have to spend a considerable amount of money to switch to HDTV. They have to buy new cameras, new titling and editing equipment, new tape machines, new rigs for their news vans -- its a big investment.
  • Cable operators have to convert all of their equipment and all of the set-top boxes in the home.
  • Communities need to agree to have new towers built for broadcast channels.

The station decides what format of DTV it will transmit. For example, Cable operators may push for 720P so they can fit more HDTV channels onto the cable. A clear pattern has yet to emerge in the industry.

How is HDTV Different?

The usual National Television Standards Committee (NTSC) analog TV screen in the U.S. has 525 scan lines, with 480 actually visible. The usual TV has an effective picture resolution of about 210,000 pixels. In the highest resolution digital TV formats, each picture contains about two million pixels. This means about ten times more picture detail on the HDTV screen! On an analog TV the lower resolution is not as noticeable because typically the screen image is constantly changing.

DTV may be in either 4:3 or 16:9 format, as shown in the following figure:

The typical TV show uses 35 mm film (or is recorded direct-to-video using NTSC equipment). In the case of film, the broadcaster converts it to an analog TV signal for broadcasting. Standard 35 mm film has an aspect ratio of 1.37:1, meaning it is 1.37 times as wide is it high. A conventional TV screen has a 4:3, or 1.33:1, aspect ratio so the conversion is easy.

To deal with HDTV's new standards, broadcasters will need to get all new equipment, such as cameras, remote broadcast units, control rooms, cables, and sound equipment. This is because Digital TV has:

  • Wider images
  • Much more detailed pictures
  • 5.1 channel CD-quality Dolby Digital (AC-3) surround sound
  • The ability to send data directly to a screen or to a PC as a download. The actual HDTV transmission is based on a 19.3-Mbps digital data stream.

The aspect ratio (width to height) of digital TV is 16:9 (1.78:1) which is closer to the ratios used in theatrical movies, typically 1.85:1 or 2.35:1. Currently broadcasters must either pan and scan the image (crop the full picture of the film down to 4:3, eliminating part of every scene in the process) or letterbox it (present the full picture only on the middle part of the screen, with black bars above and below it). With a 16:9 screen, panning and scanning a theatrical movie doesn't remove so much from the original picture and letterboxing doesn't block out so much of your screen.

What Do I Need to Buy?

If you live in an area that has active HDTV stations broadcasting these shows, then you can buy an HDTV set and enjoy the benefits of HDTV. In that case you would be a very early adopter. Currently, the FCC rules state the start-up of digital broadcasts in 2006 and the phasing out of analog broadcasts at the same time. Right now there are very few stations broadcasting and there is a digital VCR designed for HDTV. As we get closer to 2006, however, your current analog television set will either have to be replaced or you will need to buy some sort of set-top box for converting the digital signal.

To really take advantage of HDTV today, front or rear projection HDTV sets or plasma sets are recommended. Typically, sets with picture tubes over 40" cannot fit through the in the doorway of most residences. The price of these sets is extremely high right now -- in the $7,000 range or higher.

Today's HDTV sets come in two forms. HD-ready sets have the HDTV receiver/decoder built-in, while HD-capable sets require the addition of an external receiver/decoder needed to receive digital broadcasts. In an HD-capable set, the TV is essentially a monitor. You buy the receiver separately.

Be sure any television receiver you purchase has input jacks that match the connectors on the VCR, cable box, DVD player and video game console you currently own. For many years you will have to straddle the digital/analog fence, using, for example, an analog VCR on your digital TV. At the moment, there are no "standards" for what connections will appear on the back of an HDTV set. Therefore you should look for composite, S-video and component video as a minimum set of analog jacks so you can use your existing analog equipment with the new set.

DVD will look better on HDTV sets, but you will not get the highest resolution possible. DVD video does not really support HDTV, since DVD was developed before HDTV. DVD's MPEG-2 video resolutions and frame rates are very similar to NTSC formats. However, DVD can use the 16:9 aspect ratio of an HDTV set. Eventually the DVD-Video format will be upgraded to an "HD-DVD" format. If you buy one of todayÂ’s DVD players, it will not be able to play HDTV discs when they come out.

Many early purchasers will have to "go back" to a traditional outside UHF television antenna to receive the over the air (OTA) HDTV signal. The HDTV transmission system is a 8-level vestigial sideband (VSB) technique that uses UHF channels. Your antenna rotor setting for reception of HDTV signals will be easy to adjust. You either have a picture or you do not -- there cannot be a snowy image with digital technology. There also will not be any "fringe area" reception. There's no device as yet to allow a consumer to record an HDTV show off the air, so you will also have to "go back" to watching shows when they are broadcast.

If your local cable company offers digital service, it is really digital cable. Digital cable allows more channels to fit on the cable and requires a set-top box. However, it is not HDTV. The present digital cable boxes show more channels, not higher resolution. The jury is still out on when or how cable companies will carry HDTV signals.

The same is true for existing direct broadcast satellite (DBS) systems. They use proprietary digital technology. DBS systems currently deliver only NTSC-compatible SDTV signals. Check with your satellite company to see if they will have HDTV channels.

The least expensive way to see HDTV shows right now is to buy an HDTV converter for your current analog TV. However, the HDTV shows you see will look no better than DVD on your analog TV -- you will get none of the resolution and format benefits of a real HDTV set.

HDTV conversion will be a process that unfolds over several years. For example, Major networks still have to agree on what resolutions they will use. There is no FCC mandate on resolutions for the networks to follow. We are witnessing a merging of three huge industries: personal computers, entertainment, and consumer electronics. Many companies have turf to protect, and a lot of money will be spent on the conversion. That means that the process will be slow and sometimes uncomfortable. However, the ultimate destination is a significant advance -- remarkably better pictures and sound for both your TV and your computer!

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