broadcast quality video

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)