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Basic ideas for HDTV

The basic concept behind high-definition television is actually not to increase the definition per unit area ... but rather to increase the percentage of the visual field contained by the image.

The majority of proposed analog and digital HDTV systems are working toward approximately a 100% increase in the number of horizontal and vertical pixels. (Proposals are roughly 1 MB per frame with roughly 1000 lines by 1000 horizontal points). This typically results in a factor of 2-3 improvement in the angle of the vertical and horizontal fields. The majority of HDTV proposals also change the aspect ratio to 16/9 from 4/3 - making the image more "movie-like".

The following table summarizes a few of the more conventional analog HDTV proposals in comparison with existing TV systems.

Name      Prog.   Total   Active  Vert.   Horz.   Opt.    Asp.    Vert.   Horz.   freq.  
          or      lines   lines   res.    res.    view    ratio   field   field   MHz    
          inter.                                  dist.                                  
HDTV      p       1050    960     675     600     2.5H    16/9    23 deg  41 deg  8      
USA,                                                                                     
analog                                                                                   
HDTV      p       1250    1000    700     700     2.4     16/9    23 deg  41 deg  9      
Europe,                                                                                  
analog                                                                                   
HDTV NHK  i       1125    1080    540     600     3.3     16/9    17 deg  30 deg  20     
NTSC      i       525     484     242     330     7       4/3     8 deg   11 deg  4.2    
conv.                                                                                    
NTSC      p       525     484     340     330     5       4/3     12 deg  16 deg  4.2    
prog.                                                                                    
PAL       i       625     575     290     425     6       4/3     10 deg  13 deg  5.5    
conv.                                                                                    
PAL prog  p       625     575     400     425     4.3     4/3     13 deg  18 deg  5.5    
SECAM     i       625     575     290     465     6       4/3     10 deg  13 deg  6      
conv.                                                                                    
SECAM     p       625     575     400     465     4.3     4/3     13 deg  18 deg  6      
prog

NOTE: The aspect ratio of the picture is defined to be the ratio of the picture width W to its height H. The optimal viewing distance (expressed in picture heights, H) is the distance at which the eye can just perceive the detail elements in the picture.



Dave Marshall
11/5/1999