NAME

     fwc2snr - Fast Wavelet Packet Compression 2D with Signal  to
     Noise   Ratio   control  on  residuals.   Keywords:  wavelet
     compression signal noise ratio

SYNOPSIS

     fwc2snr [ -Nntap ] [ -Ootap ] [ -crrate ] [ -snrsnratio ]  [
     -buffersize ] [ -VT ] [ -V ] [ -help -h -? ]

DESCRIPTION

     fwc2snr performs very fast wavelet packet based  compression
     in  2D.  The  the header elements are compressed using gzip.
     The residual level is assigned by the user  -snr[]  and  the
     compression  rate  varies  to maintain that overall level of
     residual  in  the  decompressed  dataset.   Alternately  the
     compression  ratio can be specified using -cr[].  Simultane-
     ous use of both specifications  will  result  in  an  abort.
     Scaled input data is expected [see discussion below].
     fwc2snr gets both its data and its parameters  from  command
     line  arguments.  These arguments specify the input, output,
     the compression ratio or alternately the desired  signal  to
     noise  ratio,  the buffer size and verbose printout [with or
     without timing estimate], if desired.

  Command line arguments
     -N ntap  [stdin]
          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  [stdout]
          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  [none]
          Enter the compression ratio.  One of  -cr[]  or  -snr[]
          must be present on the command line or the program will
          abort.  A compression ratio of 15 or below  will  yeild
          essentially  lossless  compression.  Compression ratios
          above  15  will  result  in  some   loss   during   the
          compression/decompression  cycle.   The  nature  of the
          loss can be more closely controlled by using the -snr[]
          option below.

     -snr snr  [none]
          Enter the desired signal to noise ratio.  This  governs
          the  energy  level  of  the residual after one cycle of
          compression / decompression.  For instance  a  -snr[30]
          would  specify  that  the ratio of original to residual
          would be maintained at 30:1.  To check this out  simply
          compress  and  decompress a record [using ifwc2snr] and
          use the USP routine vstak to create a difference record
          between  the  output  and  the  original  input. One of
          -snr[] or -cr[] above must be present  on  the  command
          line or the routine will abort.

     -buffer rate  [system buffer size]
          enter the desired I/O buffer size.

     -VT  Enter the command line argument '-VT' to get  run  time
          estimates during execution.

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

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

DISCUSSION

     This product is licensed from Fast  Mathematical  Algorithms
     and Hardware Inc.  It is proprietary to BP Amoco and may not
     be ported to applications or locations outside  the  company
     without the expressed written permission of GeoEnergy Corp.

     As with any compression code the quality of the decompressed
     output  is  a function of the stability of the amplitudes in
     the input.  For seismic data the minimum preprocessing prior
     to  compression includes a glitch detection and removal fol-
     lowed by a spherical divergence correction.  Failure  to  at
     least  do  the latter will result in lost data in the deeper
     [and dimmer] portions of the  record.   The  level  of  loss
     increases  with  the  compression ration [or signal to noise
     ratio] requested.  The level of loss also increases with the
     amount of amplitude instability in the data.

     For other types of data [velocity, coherency etc]  a  little
     experimentation  is  manditory  to that the user understands
     the effects of compression on these data.

     A minimum level of QC would be to run  ifwc2snr  -verify  on
     the  compressed  output.   This  will  report  the number of
     records present in the compressed volume.  Since the size of
     the  compressed  volume will be much smaller that the input,
     missing records are not obvious.  If anything happened  dur-
     ing  execution  to  cause  dropped data it is a good idea to
     find out about it BEFORE you erase the original input.

     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.