broadcast quality video

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broadcast quality video - Free On-line Dictionary of Computing (26 May 2007) :

  broadcast quality video
  
     <communications, multimedia> Roughly, video with more than
     30 frames per second at a resolution of 800 x 640 pixels.
  
     The quality of moving pictures and sound is determined by the
     complete chain from camera to receiver.  Relevant factors are
     the colour temperature of the lighting, the balance of the
     red, green and blue vision pick-up tubes to produce the
     correct display colour temperature (which will be different)
     and the gamma pre-correction to cancel the non-linear
     characteristic of cathode-ray tubes in television receivers.
     The resolution of the camera tube and video coding system
     will determine the maximum number of pixels in the picture.
  
     Different colour coding systems have different defects.  The
     NTSC system (National Television Systems Committee) can
     produce hue errors.  The PAL system (Phase Alternation by
     Line) can produce saturation errors.
  
     Television modulation systems are specified by ITU CCIR Report
     624.  Low-resolution systems have bandwidths of 4.2 MHz with
     525 to 625 lines per frame as used in the Americas and Japan.
     Medium resolution of 5 to 6.5 MHz with 625 lines is used in
     Europe, Asia, Africa and Australasia.  High-Definition Television
      (HDTV) will require 8 MHz or more of bandwidth.
  
     A medium resolution (5.5 MHz in UK) picture can be represented
     by 572 lines of 402 pixels.  Note the ratio of pixels to lines
     is not the same as the aspect ratio.  A VGA display (480n
     lines of 640 pixels) could thus display 84% of the height of
     one picture frame.
  
     Most compression techniques reduce quality as they assume a
     restricted range of detail and motion and discard details to
     which the human eye is not sensitive.
  
     Broadcast quality implies something better than amateur or
     domestic video and therefore can't be retained on a domestic
     video recorder.  Broadcasts use quadriplex or U-matic
     recorders.
  
     The lowest frame rate used for commercial entertainment is the
     24Hz of the 35mm cinema camera.  When broadcast on a 50Hz
     television system, the pictures are screened at 25Hz reducing
     the running times by 4%.  On a 60Hz system every five movie
     frames are screened as six TV frames, still at the 4%
     increased rate.  The six frames are made by mixing adjacent
     frames, with some degradation of the picture.
  
     A computer system to meet international standard reproduction
     would at least VGA resolution, an interlaced frame rate of
     24Hz and 8 bits to represent the luminance (Y) component.  For
     a component display system using red, green and blue (RGB)
     electron guns and phosphor dots each will require 7 bits.
     Transmission and recording is different as various coding
     schemes need less bits if other representations are used
     instead of RGB.  Broadcasts use YUV and compression can reduce
     this to about 3.5 bits per pixel without perceptible
     degradation.  High-quality video and sound can be carried on a
     34 Mbaud channel after being compressed with ADPCM and
     variable length coding, potentially in real time.
  
     (1997-07-04)