High Definition Televisions (HDTVs)

The face of television is rapidly changing.  After 50-60 years of relatively little change in the analog standards for black and white (1941) and color television (1953) in the U.S. that were set by the National Television Standards Committee (NTSC), a new set of digital television standards are being rolled out.  Terrestrial broadcasters have been allocated additional bandwidth to introduce digital broadcasts along with their analog signals in a transition period.  Analog broadcasting is scheduled to be phased out by the end 2006.  The new technology specification, called High-Definition Television (HDTV), promises greater detail and widens the picture format to more closely match what is used in the motion picture industry.

In particular, analog NTSC television has an aspect ratio (the ratio of width to height) of  4:3 (1.33), a vertical resolution of 480 lines (interlaced) and up to 720 pixels per line.  HDTV has an aspect ratio of 16:9 (1.76) and two signal formats:  720p (progressive scan with 720 lines and 1,280 pixels per line) and 1080i (interlaced with 1,080 lines and 1,920 pixels per line).  Progressive scan processes and displays each vertical scan line in sequence.  Most computer monitors have been progressive scan for many years.  Progressive scan displays must refresh the screen fast enough to keep the image from fading before being redrawn.  Interlaced displays reduce picture flicker by alternately writing the even and odd scan lines.

Higher resolution, digital quality and better match with movie formats make HDTV a compelling step forward.  HDTV and the popularity of  DVDs (which have much better audio and video technology than videotapes) have sparked a revolution in display technologies and the “home theater” concept.   Home theater setups attempt to recreate a movie theater with surround sound from multiple speakers and a big-screen monitor that provides an immersive experience.

The consumer television manufacturers have been tackling the challenges of HDTV and home theater along many different fronts.  Many new TVs do not fully capture the 1080i or 720p resolution specifications of HDTV; nevertheless, anything above 720 lines of vertical resolution is still marketed as HDTV.  For example, they may have a native resolution of 1,024 x 1,024 pixels rather than the 1,080 x 1,920 resolution of the 1080i  spec.  The 1080i signal is converted to match the TVs native resolution.  If the native resolution exceeds the broadcast resolution, the missing pixels are interpolated.  A step down from HDTV monitors are Enhanced-Definition TVs (EDTV), which convert HDTV signals into 480p –  still superior to the 480i displays of familiar analog TVs.

TV Display Technology

Not only are the formats changing over, but newer display technologies are starting to replace the standard direct-view, cathode-ray tube (CRT) TVs that have been around for decades.  CRTs top out at about 36-38 inches and become extremely heavy and bulky.  The primary competitors to CRTs include:

• Rear projection  Rear projection used to mean large, fuzzy images with poor off-axis viewing from big, bulky cabinets.  New rear-projection TVs (RPTVs) come in much slimmer designs from improved technologies such as DLP (Digital Light Processing), LCD (Liquid Crystal Display) and LCoS Liquid Crystal on Silicon).  DLP was developed by Texas Instruments and uses nearly a million “micromirrors” to reflect light from a lamp through a color wheel onto a screen.  RPTV screens range from 40 to 82 inches, and some are only 7 inches deep.
   
• Flat Panels  The coolest big-screen TVs are undoubtedly the big plasma or LCD sets that are less than 4 inches deep.  LCDs have been very popular as computer monitors in smaller sizes for some time.  LCD TV screen sizes currently max out at 42-46 inches.  Plasma sets run from 42 to 63 inches.  The images and prices for flat panels are stunning.  The big LCDs are currently more expensive than comparable plasmas, but prices are rapidly falling for both.  Plasmas run hotter, require more power, and can suffer burn-in, but have slightly better off-axis viewing than flat panel LCDs.  My sense is that LCDs will overtake plasmas eventually.
   
• Front projection.  Front projection is like a movie theater.  You need a projector and a screen, both of which can be motorized and recessed.  You can get front projection systems that use three-tube CRTs or single lens DLP, LCD and LCoS technologies.

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Copyright 2003 by Mark Jones.
Last updated November 21, 2004.