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 COMPFACE(3)                                                     COMPFACE(3)
                               25 January 1990

      compface, uncompface - compress and expand 48x48x1 face image files

      compface (buf) uncompface (buf) char *buf

      compface is a function for generating highly compressed
      representations of 48x48x1 face image files.  uncompface is an inverse
      function which performs an inverse transformation with no loss of
      data.  The algorithm used is highly tuned for its purpose and achieves
      better than a five to one compression ratio on average.  In both
      functions, input is via a NULL terminated string and a NULL terminated
      output string is written over the input string.  Buf should therefore
      point to a block of 2K size or more to avoid buffer overruns during
      output generation.  The input format for compface (and the output
      format for uncompface) is 48 lines each of 3 sixteen bit hexadecimal
      integers, comma terminated in C initialiser style.  The output format
      of compface (and the input format for uncompface) is some number of
      lines made up of a space followed by printable characters (in the
      range ``!'' to ``~'' inclusive).  The first line contains 72
      characters and following lines contain 79 characters except that the
      last line may be short.  The amount of compression obtained varies
      between face image files but the output of compface averages less than
      200 characters.  The average number of output lines is three.

      The return value is normally 0.  1 will be returned if extra input has
      been ignored during a compress operation.  -1 is returned in the case
      of an invalid input format.  -2 is returned if an internal buffer
      overrun occurs.


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