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Section 2.4.  Digital Video                                    13

            2.4  Digital Video


            2.4.1  Why Digital?
            For  the  past  two  decades  or  so,  the  world  has  been  experiencing  a  digital
            revolution.  Most  industries  have  witnessed  a  change  from  analog  to  digital
            technology,  and  video  was  no  exception.  Digital  video  has  the  following  ad-
            vantages over analog video
               •	Ease of  editing, enhancing, and creating  special e6ects.
               •	Avoidance  of  artefacts  typical  of  analog  video,  like,  for  example,  those
                 caused by repeated recording on tapes, and errors in color rendition due
                 to inaccuracies in the separation of  composite video signals.
               •	Easy software conversion from one standard to another. For analog video
                 conversion, expensive  transcoders are  needed.
               •	Robustness to noise  and ease  of  encryption.
               •	Ease  of  scalability  (spatial,  temporal,  or  signal-to-noise  ratio  (SNR)).
                 This  facilitates  the  provision  of  the  same  service  over  a  wide  range  of
                 networks and hardware  platforms.
               •	Interactivity.
               •	Ease  of  indexing,  search  and  retrieval.  For  analog  video,  this  requires
                 tedious visual  scanning.
               These  advantages  allowed  a  number  of  new  applications  and  services  to
            be  introduced.  For  example,  the  TV  broadcasting  industry  is  introducing  new
            services  like  interactivity,  search  and  retrieval,  video-on-demand,  and  high-
            de nition  television  (HDTV).  The  telecommunication  industry  is  providing
            videoconferencing  and  videophones  over  a  wide  range  of  wired  and  wireless
            networks.  The  computer  industry  is  providing  desktop  video  and  videocon-
            ferencing.  Other  applications  include  intelligent  highway  traGc  control  sys-
            tems,  medical  imaging,  surveillance,  and  /ight  simulation,  to  mention
            a few.


            2.4.2  Digitization
            The process of digitizing video involves three basic operations:  ltering, sam-
            pling,  and  quantization.  If  the  frequency  content  of  the  input  analog  signal
            exceeds  half  the  sampling  frequency,  aliasing  artefacts  will  occur.  Thus,  the
             ltering operation is used to bandlimit the input signal and condition it for the
            following sampling  operation.
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