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High-definition television ( HDTV) refers to video having resolution much higher than traditional television systems. today HDTV is digitally broadcast using video compression.HDTV is a revolutionary technology in the television industry that produces pictures far sharper and clearer than the television most of us use today. High-definition televisions are available in four different display technologies - Projection, Directview Cathode Ray Tube (CRT), Liquid Crystal Display (LCD) and Plasma.With HDTV, you could also play movies in their original widescreen format without the letterbox "black bars".
Notation:
-Frame size in pixels is defined as number of horizontal pixels × number of vertical pixels,
-Scanning system is identified with the letter P for progressive scanning or I for interlaced scanning.
-Frame rate is identified as number of video frames per second. The color is an aspect of the HDTV that hasn't received a naming standard. Together , the 24 total bits defining color yields under 17 million possible pixel colors.

Equipment and Signal:
An antenna:
Depending on your location relative to the stations you want to watch, a set of rabbit ears might do, but you might need a rooftop or attic antenna.
Cable:
a set-top cable box or a CableCARD„¢ to allow your television to receive and decode the cable HDTV signal.
Satellite service:
You may need a different satellite dish and tuner to receive HDTV signals via satellite.

Types of media:
Standard 35 mm photographic film used for cinema projection has higher resolution than HDTV systems, and is exposed and projected at a rate of 24fps.Non-cinematic HDTV video recordings intended for broadcast are typically recorded either in 720p or 1080i format as determined by the broadcaster.

Recording and compression:
HDTV can be recorded to D-VHS to an HDTV-capable digital video recorder. Some cable boxes are capable of receiving or recording two or more broadcasts at a time in HDTV format, and HDTV programming. The data involved are massive. A Hauppauge 1212 Personal Video Recorder is used for this purpose. This device accepts HD content through component video inputs and stores the content in an uncompressed MPEG transport stream (.ts) file or Blu-ray format .m2ts file on the hard drive. digital HDTV signal conversion to MPEG-2 compressed signal in real time is prohibitively expensive.

For further details, visit these links:
http://en.wikipediawiki/High-definition_television
http://electronics.howstuffworkshdtv.htm
http://mansci.journal.informscgi/content...39/11/1319

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DEFINITION:
HDTV is generally recognized as a digital video broadcast with a minimum resolution of 1280 pixels wide and 720 pixels high, a rate of 30 or more frames/second and usually an aspect ratio of 16:9.
A standard definition analog television uses a cathode ray tube with an electron gun to guide the path of an electron beam to “paint” 480 vertical lines across the face of the screen. Each time the beam strikes a dot of phosphor, light is produced. For a color television set, each spot consists of a group of three phosphor elements; one for each primary color.
Analog To Digital Conversion
Signals in the real world are analog: light, sound, you name it. So, real-world signals must be converted into digital, using a circuit called ADC (Analog-to-Digital Converter), before they can be manipulated by digital equipment