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What is HDTV

written by: Debasis Das•edited by: Rhonda Callow•updated: 7/11/2011

More and more people are moving to HDTVs. Check out this article if you're wondering how HDTV differs from traditional televisions or want to know how HDTV works.

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    There is no simple answer to the question “How does HDTV work?" It basically depends on what type of HDTV you are asking the question about. There are quite a few types. Depending on if it's an LCD or a plasma television or an LED TV set, the workings will be different to some degree. So it is possible to answer the question “how does a plasma HDTV work?" but not the general one. However, we can go about answering a few general questions, such as what does it mean for a TV to be an HDTV, and so on. Then we can look at some of the most popular HDTV technologies of the day.

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    What is HDTV?

    What separates HDTV or high definition television from traditional TV that we have been used to for many decades are the aspect ratio and the resolution. While traditional TV was at an aspect ratio of 4:3, HDTV is at a more natural movie-like aspect ratio of 16:9. Viewers of traditional televisions can easily visualize a 16:9 aspect ratio by remembering the black rectangles that could be seen when viewing many widescreen DVDs. (Note that 16:9 translates into an aspect ratio of 1.78, while cinema aspect ratio is usually 1.85 or even higher.)

    The other significant difference is in resolution. This really gives the HDTV a true enhancement. While older TV sets usually used 480 vertical scanning lines (note that the terminology is a bit misleading because the actual scan happens horizontally from left to right for each line, and then proceeds vertically downwards line-by-line), or sometimes 576 lines; high definition uses at least 720 lines, and full HD uses 1080 lines. This gives HD a resolution of either 1280x720, or for full HD 1920x1080 (that is how many horizontal x vertical pixels that are required to maintain the aspect ratio of 16:9). The ‘p’ or the ‘i’ signifies the scanning methodology used. ‘i’ indicates interlaced scanning in which only half of a frame is drawn first (odd lines) followed by the other half (even lines). This was the method used in traditional TV sets. The ‘p’ refers to progressive scanning in which an entire frame is built and displayed line-by-line at one time.

    Between the aspect ratio and the much higher resolution your viewing experience is enhanced. The 16:9 ratio that caters to a comparatively larger horizontal span of your display allows for more natural movement of people on screen. The much higher resolution gives you more natural, lifelike pictures justifying the name high definition. "HDTV buyer's Guide: An Intro to HDTV"; this first part of a series of articles has a good coverage.

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    Types of HDTVs

    There are several types of HDTVs available today:

    Plasma TV

    This technology encloses a gas between two sheets of glass, and depending on how the gas is energized it emits ultraviolet of a certain energy, which in turn excites phosphors on the plasma TV screen to produce a visible light image. They produce a wonderful image with brilliant colors and high contrast. They are however bulkier than say LCDs or LEDs and also more fragile. They do not work well at altitudes greater than 6000 feet.

    Flat Panel LCD TV

    This technology is the same as your laptop screens and flat panel computer displays. Each individual pixel is displayed by the action of liquid crystals. These are extremely light weight and consume very little power. They have the potential problem of dead pixels and are difficult to view at wider viewing angles.

    LED TV

    This is a variation on LCD technology that uses LEDs instead of fluorescent lighting as the backlight. These provide better viewing angles, brightness and contrast ratios than traditional LCD technology. They also don’t use any mercury and have a lesser environmental impact. However, it will likely take some time before they become as inexpensive and as common as LCD TVs. Perhaps around the same time as all programming becomes HDTV.

    There are a few other technologies such as Digital Light Processing (DLP), some projection-based, as well as CRTs, but each of these, it appears, is becoming less and less popular. Look up the article "HDTV buying Guide: Wrapping things up" for a overall sum up.