资料来源 : Free On-Line Dictionary of Computing

broadcast quality video
     
         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)