NAME

     lch2 - Local Cosine - Uniform Bin Width Quantization - Huff-
     man Coding Compression

SYNOPSIS

     lch2 [ -Nntap ] [ -Ootap ] [ -crcr ] [ -V ] [ -h ] [ -? ]

DESCRIPTION

     lch2 performs local cosine uniform  bin  width  quantization
     huffman   coding.   The  algorithm  uses  2-D  local  cosine
     transform algorithm,  uniform  bin  width  quantization  and
     Huffman coding.
     lch2 gets both its data and its parameters from command line
     arguments.   These  arguments specify the input, output, the
     compression ratio, and verbose printout, if desired.

  Command line arguments
     -N ntap
          Enter the input data set name or file immediately after
          typing -N unless the input is from a pipe in which case
          the -N entry must be omitted.  This input  file  should
          include the complete path name if the file resides in a
          different directory.  Example -N/b/vsp/dummy tells  the
          program to look for file 'dummy' in directory '/b/vsp'.

     -O otap
          Enter the output data  set  name  or  file  immediately
          after typing -O.  This output file is not required when
          piping the output to another process.  The output  data
          set also requires the full path name (see above).

     -cr cr
          Enter the compression ratio.  The default is the  value
          of  15.  For the default value, in prestack data we get
          visually lossless compression.

     -V   Enter the command line argument '-V' to get  additional
          printout.

     -? or -h
          Enter the command line argument '-?'  or   -h   to  get
          online  help.   The  program  terminates after the help
          screen is printed.

DISCUSSION

     This code performs 2-D tensor local cosine transform -  Uni-
     form  quantization  -  Huffman coding compression of seismic
     data. The output compressed file  starts  with  the  seismic
     header losslessly compressed by gzip, the compression header
     (which includes parameters,  such  as  local  cosine  window
     lenghts, quantization bin widths, Huffman codes) followed by
     the  Huffman  coded,  quantized,  2-D  local  cosine  tensor
     transform coefficients.

     It is important to have amplitude balanced data  going  into
     this  routine.   By  balanced we mean at least corrected for
     spherical divergence.  A simple  ttothen  does the trick  on
     most  data.   The more attention paid to preconditioning the
     data  for  compression  [direct  arrival  removal,  bandpass
     filtering,   spherical  divergence  compensation  etc.]  the
     greater the compression attained and the lower the residuals
     after a cycle of compression / decompression.

DISCUSSION

     This  product  is  licensed  from  GeoEnergy  Inc.   It   is
     proprietary  to  BP  Amoco and may not be ported to applica-
     tions or locations outside the company without the expressed
     written permission

BUGS

     none known at present

AUTHOR

     Anthony Vassiliou (GeoEnergy Inc.  918-494-4641),  Joe  Wade
     (socon 421-3324)

COPYRIGHT

     copyright 2001, Amoco Production Company
               All Rights Reserved
          an affiliate of BP America Inc.