DIGITAL TELEVISION I. WHAT IS DIGITAL TELEVISION AND HOW IS IT IMPORTANT AND USEFUL? (http://www.howstuffworks.com/dtv.htm) Believe it or not, Digital Television, or DTV, can change your life, if you are a TV fan. Imagine your normal TV 10 times clearer. DTV has a sharper and wider display and a much more clear and crisp picture. It also has amazing sound and high resolution. (Resolution controls the crispness and the detail that you see on your TV. This is based on the amount of pixels on the screen, which I will describe later.) It seems like a movie screen, rather than a TV set. HDTV, or High Definition Television is even better than DTV. It has the highest resolution combined with Dolby Digital Surround Sound. In order to have a DTV or HDTV in your home, you must first check if your area provided active HDTV stations. In 2006, the television will begin phasing out analog television and bringing in HDTV broadcasting. Therefore, people will be required to buy converters that convert the digital signal or buy a complete new set all together. There are HD-ready sets that have the HDTV receiver and decoder that are built into it. There are also HD-capable sets, in which the receiver is a monitor basically and you need to use and external receiver and decoder. This is called a set-top unit. DTV and HDTV are not the same as digital cable and direct broadcast satellite systems. These both use different digital technology that does not have a higher resolution. II. HISTORICAL BACKGROUND (http://www.ee.washington.edu/conselec/CE/kuhn/hdtv/95x5.htm and http://www.dcita.gov.au/graphics_welcome.html) The ideas for HDTV originally came from the idea of movies. People enjoy wide screens and enjoy being up close into the action. Movie producers noticed this. It increases the feeling of actually “being there.” In the late 1970’s Sony and NHK developed a high-definition television system called NHK Hi-vision. In the early 1980’s, they offered this to movie producers. This system produced a picture like that of a 35 mm film. A film could be recorded, played, and edited. It then went back on the film. Special effects were also revolutionized by this system. The old conventional film ways were eradicated. Since this was happening on the film industry, people began wondering is it could be used for commercial broadcasting that would have twice the amount of horizontal and vertical lines of a regular TV set. The only problem with making such a device would be its compatibility with regular TVs. In 1954, they had the same problem when introducing the color TV. In 1954, the US picked compatibility. When making the HDTV, they are broadcasting both analog TV (regular) and HDTV simultaneously. They call it “simulcasting.” This simulcast period will end when the government decides. This will most likely be when most people have bought the system or set top units and it is affordable. They are also using the compatibility strategy. The FCC, which makes all decisions regarding it, will make all decisions relating to this problem. III. HOW IT ACTUALLY WORKS (http://howstuffworks.com/dtv.htm, http://howstuffworks.com/tv1.htm, and http://howstuffworks.com/hdtv.htm) Your brain is what allows you to see what is on a television screen or monitor of a computer. First, we must understand the basic concepts of a TV and what allows you to see a picture. You divide a still image into a collection of small colored dots and assemble these into an image. The following picture shows this by blowing these dots up so that you can understand how the brain does this (stand about 15 feet from your computer in order to reassemble the image): (howstuffworks.com) These dots are called pixels. TVs, computers, newspapers, and magazines use them. In order to see a moving scene, your brain sees still pictures moving in a rapid succession. All TVs have a Cathode Ray Tube. In the following picture, you can see this diagram. The anode is the positively charged terminal and the cathode is negatively charged. The cathode is a heated filament, like that of a light bulb. In fact, you could make a screen of a TV using tons and tons of 60 W bulbs!! The cathode is inside a vacuum in a glass tube and a ray is a stream of electrons that come off the heated cathode in the vacuum. Since the anode is positive, it attracts the negative electrons coming off. This stream is focused by an anode in a tight beam. It is then accelerated by an accelerating anode. This high-speed beam goes through the tube and hits a flat screen that is coated with phosphor. This glows when it is hit by the beam. The steering coils work through electromagnetism, which we have previously studied. These coils create magnetic fields and the beam responds to these. One field makes the beam go vertically and another makes it go horizontally. You can position the beam by controlling the voltage of the coils. INSIDE A TV: THE COILS: (howstuffworks.com) To get color, three beams, red, green, and blue, move along the screen simultaneously. The screen is coated in red, green, and blue phosphors that are arranged in dots or stripes that can be seen with a magnifying glass. A shadow mask, a thin metal screen, is on the inside of the TV close to the coating. You can see this here: A: PHOSPHORS, B: SHADOW MASK, C: GLASS As we have learned in color and light, all three colors make individual colors, combine to form white, or mix in different ways forming all different colors. A color TV reads and decodes signals that tell it what colors to use. The chrominance signal has a phase shift that tells it what color. This is wave. Its amplitude determines the saturation. The number of degrees of the shift decodes the color. Basically, that is how light is involved in TVs DTVs and HDTVs work in the same way of deciphering color. However, the main difference that makes these much clearer and crisper is pixels. In analog TVs, the camera turns one picture into rows of pixels. Each individual pixel has an assigned color and intensity. These rows are combined with synchronization signals, which are called horizontal and vertical sync. The electronics inside a TV know how to display these rows. The final signal is the composite video signal. Sound has a separate signal. These signals can be broadcasted through radio waves, which we have previously studied, recorded on a VCR, or transmitted through a cable system. Different channels have different frequencies. They work like a radio. DTV, however, used higher resolutions. That is the main difference. Resolution determines the detail and crispness. It is determined by the number of pixels on the screen. An analog TV uses a process of interlacing. There are 525 horizontal lines of resolution every 13th of a second, but what actually happens is that half are shown in a 16th of a second and the other half are shown in the next 16 th of s second. Therefore the whole frame is updated every 13th. Nowadays, computer screens display many more pixels, and so analog TVs look fuzzier than screens. On DTVs and HDTVs, there are up to 10 times more pixels that are digitally precise. The picture is stable, clear, and fantastic. There is no comparison! It is quite obvious. You can see the dramatic difference in the next two pictures: DTV: ANALOG TV: There are different formats of DTVs and HDTVs, which mean the number of pixels. There is 480p and 480i, which are known as standard definition (SD) that have a picture of 704x480 pixels sent at 60 frames per second. There are also 720p (1280x720 pixels at 60 frames per second) and 1080i (1920x1080 pixels at 60 frames per second) which are known as high definition formats (HD.) The “p” is short for progressive, which means the picture is updated every 16th of a second, and the “i” is short for interlaces, which updates half the picture every 16th. HD formats have a different aspect ration than analog TVs, which is the size ratio. An analog is 4:3 and a HD is 16:9: A show is decoded by a MPEG-2 compression used by broadcasters. It allows you to pick screen size and bit rate while encoding the show. Different numbers are picked depending on the show. For example, a sporting event would use a bigger screen, such as a 1080i, and more megabits per second, whereas a new report might use a 480p and less megabits. IV. CONCLUSION I think that this topic was very fun to do since it’s an application of light that is involved in daily life and is a big deal in America right now. The sites I used were very helpful in understanding and retaining the information. I was able to learn a great deal about the topic. Everything we learned about electromagnetism, radio waves, light bulbs, voltage, and great amount of information on color were ALL able to be applied and used in understanding this topic. I am glad I picked it and look forward to learning more about this and other topics in the future. V. BIBLIOGRAPHY 1. Brain, Marshall. “How Digital Television Works.” Online. Available: http://www.howstuffworks.com/dtv.htm. Access Date: 2/9/02. 2. Brain, Marshall. “How Television Works.” Online. Available: http://www.howstuffworks.com/tv1.htm. Access Date: 2/9/02. 3. Brown, Gary. “How HDTV Works.” Online. Available: http://www.howstuffworks.com/hdtv.htm. Access Date: 2/9/02. 4. “Digital Television: The Site-What is Digital Television (DTV)?” Online. Available: http://www.digitaltelevision.com/consumer/what.shtm;. Access Date: 2/12/02. 5. “HDTV,” Microsoft Encarta Encyclopedia 2000. 6. Kuhn, Kelin J. “HDTV: An Introduction,” Online. Available: http://www.ee.washington.edu/conselec/CE/kuhn/hdtv/95x5.htm. Access Date: 2/11/02. 7. “What is Digital Television: Fact Sheet,” Online. Available: http://www.dcita.gov.au/graphics_welcome.html. Last Updated: 3/23/1998. Access Date: 2/10/02.
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