High-Definition Television

From the beginning of time, ideas have been dreamt up and contemplated. Dreams like capturing electricity to make light, instead of using a candle or sunlight. One particular dreamer that revolutionized all forms of entertainment was a 14-year-old boy named Philo T. Farnsworth. Philo came up with the idea of capturing light in a jar and transmitting it in a series of individual lines with electron beams. This wonderful theory became the first Black-in-White Television. Shortly after, this technology touched the brink of another dream, color. In the 1950ís, technology came out with the first color televisions, but the bananas looked blue. Later, the quality of color was improved, people started trading in their black-and-white sets for the ones that showed green grass and the blue sky. Consequently, the quest for better image quality recursively continued, which now will eventually force your living room to endure another makeover, it is called High Definition Television (HDTV). Digital signals will be used to make screens sparkle with crystal-clear images. Also these new-age TVís will have a wide picture and CD-like sound that will transform homes into high-tech theaters. The following question will help you better understand HDTV.

  • What is HDTV?
  • How did HDTV begin?
  • HDTV versus NTSC.
  • What is 30-Degree Field of Vision Important?
  • Letís talk About Color.
  • Letís talk About Sound.
  • Problems Faced by HDTV.
  • Will I need to buy a new TV?
  • Bandwidth Limitations.
  • Digital Signals and Bandwidth Squeeze.
  • What is MPEG-2 Technology?
  • What is the FCC Ďs role in HDTV?
  • What is the Grand Alliance?
  • Frequently Asked Questions

What is HDTV?

The Federal Communications Commission (FCC) defines HDTV (High Definition Television) as a system that nearly doubles the capabilities of NTSC (National Television Systems Committee) standard, the system currently being used the United States. HDTV will offer almost 2 times the horizontal and vertical resolution of the current system [8]. Basically, the viewer will have a picture quality close to that of 35-mm film and the digital sound will be extremely close to a compact disk. HDTV will offer an extremely sharp, photographic-quality picture. In addition, HDTV will feature up to 1080 lines of resolution. HDTV will have Dolby Digital sound quality and a larger field of vision that will make watching programs like sporting events more life like.

How HDTV Begin?

The original stimulus for HDTV came from wide-screen movies. Soon after the wide-screen was introduced, movie producers discovered that individuals seated in the first few rows enjoyed a level of participation in the action not possible with conventional movies. Evidently, having the screen occupy a great field of view (especially peripherally) significantly increases the sense of "being there" [1].

In the late 1970ís and early 1980ís, NHK and Sony developed and presented a high-definition television system to movie producers. The system was called "NHK Hi-vision" and it was capable of producing images that have the same detail as 35-mm film. This system could take a scene and immediately transfer it to film after recording and editing it. This caused many of the intermediate delays in conventional film production to be eliminated [9].

After HDTV spread into the film industry, Commercial broadcasting became interested in this exciting technology. Commercial broadcasting began to generate ideas of how HDTV would now bring a new essence of advertising and marketing into society. For example, ball games would now be more life-like, with the increase in sound quality and resolution. However, as more anticipation for HDTV grew from the commercial industry, questions started to arise about the standards the NTSC versus HDTV.

HDTV versus NTSC

HDTV is a digital television system, which offers many advantages over the traditional television system called The National Television System Committee (NTSC) of the Electronics Industries. In order to understand these differences, first you must understand what HDTV is trying to do. The basic concept behind high-definition television is actually not to increase the definition per unit area, but to increase the percentage of the visual field contained by the image. HDTV demonstrates this idea by using a rectangular spectrum ratio of 16:9 (Width: Height), which happens to be shaped live a movie screen [6]. The National Television System Committee (NTSC) spectrum ratio almost looks like a box with the dimension of 4:3 (Width: Height), which broadcasts 30 frames per second with 525 lines per frame. NTSC uses 340 lines of vertical and 330 lines of horizontal resolution. Consequently, HDTV increases its vertical resolution to 675 and horizontal resolution to a range between 720 and 1080 lines [6]. As a result, HDTV produces a crystal clear sharp image, even when sitting up close to the TV set.

Not only had HDTV increased its vertical and horizontal resolution by almost 100%, but also the proscribe distance is much closer to the screen. For example, if the screen is 1 ft tall, the proscribed viewing distance is 3 ft from the screen. This is the precise reason for widening the screen is to provide a 30-degree field of vision for the viewer. This occurs when viewing exactly at the proscribed distance [9]. A 30 degree field of vision is dramatically more "real" for the viewer compared to a ten degree field of vision, which is customary with the NTSC standard at the 8 to 10 picture heights distance. The key to understanding the difference between HDTV and standard TV is that clarity is a matter only of distance. Distance relates directly to how great your field of vision is. A 30-degree field of vision for the viewer is the goal of HDTV.

What is 30-Degree Field of Vision Important?

The most critical point to understand is what the significance is of a 30-degree viewing field. It was determined from scientific experiments and with specific tests at NHK that the human visual system operates in two distinct ways. One, the central portion of your vision is quite sensitive to detail. You can read or see work in front of you with great perception. But this central portion is not very good at fast motion detection. If you move something rapidly across your eyes; it becomes a meaningless blur. Moreover, if your peripheral vision is just ten degrees from the center of the TV set, you begin to lose detail sharpness. A television program should provide a viewer with a greater sense of reality in both sharpness of the central vision, and motion detection in the peripheral vision. Both of these qualities need to be stimulated at the same time, for more enjoyable viewing. Through scientific research NHK proved at 30 degrees these two qualities would be satisfied, but above or below 30 degrees there is a dramatic fall off [9]. (See Appendix A, 30-degree picture).

Letís talk About Color

Although the NTSC standard TVs can be viewed with great color, it maybe because your eye is trained to the analog set. HDTV carriers five times the color information over the NTSC standard TV set. Color definition has been a problem in the past defining different intensities of the color spretrum. Color intensities will be enhanced dramatically. The color will be enhanced because four and a half HDTV pixels with fit in 1 NTSC pixel. (See Appendix B). To give you a better idea of the color intensity, just think of HDTV as a Kodak picture that moves.

Letís talk About Digital Sound

Remember when CDís first appeared on the market and most people were skeptical about these silver discs. People soon discovered the sound was great, actually it was more than great. You could listen to your favorite song and hear sounds off the CD that you never heard off a radio or tape cassette. Everyone that listened to CDs could hear a definite improvement. Now CDs have taken over the commercial music industry, but television is still in the dark ages of analog. Just like music evolve from tape (analog) to CD (digital), HDTV is following the same path. HDTV will broadcast sound using the Dolby Digital/AC-3 audio encoding system [5]. It is the same digital sound used in most movie theaters, DVDs, and most home theater systems since the early 1990ís. It can include up to 5.1 channels of sound: three in front (left, center, and right), two in the back (left and right), and a subwoofer bass for a sound you can feel. Truly, sound on a HDTV system will be CD quality with a range of frequencies lower and higher than most of us can hear. (See Appendix C).

Problems Faced by HDTV

The most significant problem faced by HDTV is exactly the same problem that color TV faced in 1954. There are approximately 600 million television sets in the world and 70% of those television sets are in color [11]. This is an important and critical standard that should be compatible with the existing color TV sets. With this point in mind, there is a strong precedence for both a compatible and simultaneous broadcast. In some areas broadcaster will plan to run future broadcasts in parallel with the understanding that the existing standards with eventually be phased out. But, what does this mean for your existing TV?

Will I need to buy a new TV?

Good news, the answer is no. Several companies like Panasonic, Sharp, and Sony are releasing set-top boxes that will make digital signals work on standard TVs. Currently, these boxes are very expensive ranging from $1,500 to $2,000. Another thing to keep in mind that as with any first-generation version of a brand new technology, it may not work perfectly. However, it is a safe bet that converter boxes will become cheaper, better, and more common over the next few years. I personally do think that anybody wants million of viewers locked out of television simply because they cannot afford a converter box or a HDTV. The moral is that the NTSC standard is here to stay for a long while, and converter boxes will get cheaper and cheaper as digital technology encompasses the United States.

Bandwidth Limitations

Another problem that HDTV faces is how much bandwidth to use. A conventional NTSC image has 525 total lines and they are scanned at 29.97 Hz, with a horizontal resolution of 427 pixels. Assuming that there are 2 pixels per video cycle, this makes 3.35 MHz as a minimum bandwidth to carry the video information without compression [6]. Current terrestrial channel allocations are limited to 6 MHz.

If one decides to move to a HDTV system, the HDTV image will have 1050 lines with 600 pixels (keeping the same frame rate). Moreover, this means the bandwidth would have to be 18 MHz [6]. Obviously, there is a definite problem in the current terrestrial channel allocation or conventional wireless TV transmission, which is limited to 6 MHz.

The options for terrestrial broadcast (assuming a 20 MHz bandwidth) are roughly as follows:

1. Change the channel allocation system from 6 MHz to 20 MHz.

2. Compress the signal to fit inside the 6 MHz existing bandwidths.

3. Allocate multiple channels (2 with compression or three without) for the HDTV signal. [12]

Options 1 and 2 are practically incompatible with current NTSC service. About the only possibility for maintaining compatibility is a coexisting broadcast of NTSC information over certain channels and HDTV information over other channels. However, this might hurt both the NTSC and HDTV. Option 3 does allow compatibility, by making the first 6 MHz of the signal keep to the standard of the NTSC broadcasting and the remaining signal is an additional augmentation signal for HDTV. Typically, in this type of augmentation system, an existing VHF channel would be tied to one (or two) UHF channels. The VHF channel would carry information similar to the current NTSC signal and the UHF channel (or channels would carry augmented high-resolution information) [12].

Digital Signals and Bandwidth Squeeze

Contrary to popular opinion, a digital signal is not needed to conduct a HDTV broadcast. Did you know the Japanese broadcast HDTV over an analog signal? So why is the United States switching from analog to digital? There are several good reasons to convert to digital, which include: More data can be transmitted, data rates are more consistent over longer distances, and the multiple types of data the signal can carry. An important thing to note is that you can stuff a lot more information into a digital signal versus an analog signal. United States does not have the same luxury as other countries with more bandwidth to use. Since HDTV requires more detail to be sent; a digital signal is required with compression techniques to squeeze the HDTV information into its bandwidth limitations. (See Appendix D). Another interesting fact about digital over analog signals is resiliency over distance. Both analog and digital signals get weaker with distance. However, digital signals can be regenerated and remain perfect, unlike the fading and fuzzy signals. Clearly, converting to digital broadcast is a wise move for the future.

What is MPEG-2 Technology

MPEG stands for Moving Picture Experts Group. MPEG is the standard used for compression. MPEG technology takes advantage of how the eye perceives color variations and motion. MPEG-2 technology was designed for coding interlaced images at transmission rates above 4 million bits per second. A newer standard, MPEG-2, offers resolutions of 720x480 and 1280x720 at 60 bps, with full CD-quality audio. MPEG-2 can compress the amount of bits by about 55 to 1 [4]. This is sufficient for all the major TV standards, including NTSC, and even HDTV.

Basically inside each frame, and MPEG-2 encoder records just enough detail to make it look like nothing is missing. (See Appendix D). The encoder also compares adjacent frames and only records the sections of the picture that have moved or changed. If only a small section of the picture changes, the MPEG-2 encoder only changes that area and leaves the rest of the picture unchanged.

MPEG-2 is also used by DVD-ROMís. MPEG-2 can compress a 2-hour video into a few gigabytes. While decompressing an MPEG-2 data stream requires only modest computing power; encoding video in MPEG-2 format requires significantly more processing power. MPEG-2 not just a standard, but it is a kid of tool kit of syntactic elements that has a range of compression grades that vary in performance. It also provides a level of flexibility necessary to deal with transmitting and decompressing different types of pictures. The compression is achieved using five different compression techniques:

  1. The use of a frequency-based transform called Discrete Cosine Transform (DCT).
  2. Quantization, a technique for losing selective information (sometimes known as lossy compression) that can be acceptably lost from visual information.
  3. Huffman coding, a technique of lossless compression that uses code tables based on statistics about the encoded data.
  4. Motion compensated predictive coding, in which the differences in what has changed between an image and its preceding image are calculated and only the differences are encoded.
  5. Bi-directional prediction, in which some images, is predicted from the pictures immediately preceding and following the image. [3]

Although MPEG-2 is a good compression scheme it has some problems. One problem is that it is a "lossy" compression method. This means that a higher compression rate gives a poorer picture. Also, there is some loss in picture quality between the digital video camera and what you will see on your television. However, the quality is still better than a average NTSC TV set.

What is the FCCís role in HDTV?

The FCC began to organize its efforts in 1987 to design a broadcast standard for HDTV. HDTV in the USA has gone from a system with digital compression and analog transmission to a hybrid digital/analog transmission system and is planning to go to an all-digital system [2]. The proposed design placed heavy emphasis on a progressive computer, MPEG-2 compression, and decompression techniques. The proposed system encompasses multiple picture formats and frame rates and a flexible transport channel that shares video and audio signals.

During the last 7 years of HDTV proposals, testing, and FCC recommendations, a Grand Alliance was formed to help bring HDTV signals to the US. The Grand Alliance includes AT&T, General Instrument Corp, the Massachusetts Institute of Technology, Philips Consumer Electronics, Thomson Consumer Electronics, The David Sarnoff Research Center, and Zenith Electronics Corp. The alliance decided on four main technologies that will be at the forefront of the digital HDTV system.

  • Digital video-compression technology based on MPEG-2 parameters, including the use of B-frames(BI-Direction frames for motion compensation);
  • Data-transport system based on packets of virtually any combination of video, audio, and data.
  • Interlaced and non-interlaced (progressive) scanning capabilities.
  • Emphasis on the 5.1-channel Dolby AC-3 audio technology for digital surround sound [2].

What is the Grand Alliance?

The Grand Alliance standard differs from all existing TV standards in three major ways. First, the Grand Alliance wants an all-digital standard, which would be broadcast with a packet transmission. Second, it supports multiple formats. Third, it is designed to be primarily compatible with computers rather than the existing NTSC television [10].

The Grand Alliance system is both a data compression scheme, using MPEG-2 technology, and a channel-coding scheme, using the 8 VSB method offered from Zenith. The MPEG-2 compression standard was made in order to be a part in the international effort in standardizing digital compression/decompression. The choice of 8 VSB proved in testing to be the most robust against the QAM (Quadrature Amplitude Modulation) candidate. VSB proved to have the longest reach (from a transmitter) under interference-laden conditions [10]. This means you can live a little farther from a tower, have more cars and airplanes go by, have adjacent channels closer in, and even have channels using the same frequencies not so far away and still receive perfect HDTV pictures. But millions of analog's viewers are in remote areas that may not be able to receive the digital signal with the same kind of antennas they use to get on their old analog NTSC sets. This fact has worried broadcasters, since antennas have worked for viewers in near and remote areas. Any shortening of the viewing radius from a tower means either expensive repeaters, or a loss in revenue.

Frequently Asked Questions

What does Plasma Flat Screens have to do with HDTVs?

Plasma is a new kind of technology that uses tiny packets of glowing gas, rather than thicker cathode-ray tubes, to display a picture on a screen. It has higher resolution and richer color than regular cathode-ray sets, and it does not take up much space in the actually TV set. Plasma screens can be found in regular, digital, and HDTVs. As a result, these thin and futuristic-looking screens are really expensive ($10,000 for more).

Whatís the difference between HDTV and a digital-ready TV

Not all companies use the same definition, but most of the industry agrees that HDTVs should be able to receive and display all 18 digital TV formats approved for broadcast in the United States. In addition, they must have a wide screen aspect ratio and must be able to display pictures at a better resolution than todayís analog sets. Digital-ready TVs or HDTV-ready TVís do not receive digital signals, moreover they have no built in decoder. Instead, they have an input so that, eventually, you will be able to get a separate decoder box, hook it to your set, and have a digital TV that can receive HDTV programming. You can buy these TVs with wider screens and progressive scanning, but the resolution will not be the same and they are very expensive.

Will HDTV mean more channels?

Definitely! Digital signals can carry far more information than the current analog signal, which makes them perfectly suited for the high-bandwidth requirements of HDTV. However, the FCC left the door open for broadcasters to carry signal at lower resolution as well. Digital and HDTV standards require a lot of extra space. Due to this fact, it is possible for local network affiliates to split off their signals into four separate standard-definition channels. This is called SDTV multicasting, which presents combinations of broadcasting 2 standard channels and 1 HDTV channel [12]. The FCCís thinking is that if HDTV never takes off, broadcasters will use their extra bandwidth to show multiple channels.

When can I get HDTV in my Area?

The FCC has mandated a gradual rollout of digital TV, including HDTV. By May 1999, all network affiliates in the top ten markets will begin sending digital signal. It has been estimated that this December, the range will expand to the top 30 markets. Even so, HDTV is very expensive to produce, and the networks have only agreed to about five hours of programming per week. More ominously, some critics claim that receiving HDTV broadcast over the air signal is extremely difficult without a large antenna aimed directly at a local DTV transmitter. Moreover, local broadcasters are running into stumbling blocks, trying to find land for new digital transmitters. Another problem is that broadcasters have complained about transmitting the Dolby Digital sound with todayís lacking equipment. Due to these problems, deadlines have slipped off until late in the year 2001. (See Appendix E).

Conclusion

HDTV is a noble idea for moviegoers, sports fans, and the general couch potatoes. It is expensive, an average HDTV system cost between $12,000 and $25,000. I personally do not feel HDTV will make a big impact for a long time to come. People take a long time to adapt to new technology, unless you are taking about the Internet, which is relatively cheap compared to a HDTV system. As long as the FCC poses limitations on bandwidth capacity, HDTV will remain expensive. Technology will eventually overcome this limitation by the means of cheaper, smarter chips, increased growth in digital technology applications, and the push for the United States to master HDTV first.