NAME

       fpack - FITS image compression program

SYNOPSIS

       funpack [OPTION]... FILE...

DESCRIPTION

       fpack  is  a  utility program for optimally compressing images in the FITS data format.  This programs is
       analogous to the GZIP utility program except that it is optimized for FITS  format  images  and  offer  a
       wider choice of compression options.

OPTIONS

       Flags must be separate and appear before filenames. Use '-' to read from stdin.

       The compression parameters specified on the fpack command line may be overridden by compression directive
       keywords in the header of each HDU of the input file(s).

       -r     Rice compression (default).

       -h     Hcompress compression.

       -g     or -g1  GZIP_1 (per-tile) compression.

       -g2    GZIP_2 (per-tile) compression (with byte shuffling).

       -p     PLIO compression (only for positive 8 or 16-bit integer images).

       -d     Tile the image without compression (debugging mode).

       -w     Compress the whole image as a single large tile.

       -t axes
              Comma separated list of tile dimensions (default is row by row).

       -q level
              Quantized level spacing when converting floating point images to scaled integers. (+value relative
              to  sigma of background noise; -value is absolute). Default q value of 4 gives a compression ratio
              of about 6 with very high fidelity (only 0.26% increase in noise).  Using q values  of   2,  or  1
              will  give  compression ratios of about 8, or 10, respectively (with 1.0% or 4.1% noise increase).
              The scaled quantized values are randomly dithered using a seed value determined  from  the  system
              clock  at run time.  Use -q0 instead of -q to suppress random dithering.  Use -qz instead of -q to
              not dither zero-valued pixels.  Use -qt or -qzt to compute random dithering seed from  first  tile
              checksum.   Use  -qN  or  -qzN,  (N  in  range  1  to  10000)  to  use  a specific dithering seed.
              Floating-point images can be losslessly compressed by selecting the GZIP algorithm and  specifying
              -q  0,  but  this is slower and often produces much less compression than the default quantization
              method.

       -i2f   Convert integer images to floating point, then quantize and compress using the specified q  level.
              When  used  appropriately, this lossy compression method can give much better compression than the
              normal lossless compression methods without significant loss of  information.   The  -n3ratio  and
              -n3min  flags  control  the  minimum  noise  thresholds;  Images  below  these  thresholds will be
              losslessly compressed.

       -n3ratio
              Minimum ratio of background noise sigma divided by q.  Default = 2.0.

       -n3min Minimum background noise sigma. Default = 6. The -i2f flag will be ignored if the noise  level  in
              the image does not exceed both thresholds.

       -s scale
              Scale  factor  for lossy Hcompress (default = 0 = lossless) (+values relative to RMS noise; -value
              is absolute)

       -n noise
              Rescale scaled-integer images to reduce noise and improve compression.

       -v     Verbose mode; list each file as it is processed.

       -T     Show compression algorithm comparison test statistics; files unchanged.

       -R file
              Write the comparison test report (above) to a text file.

       -table Compress FITS binary tables using prototype method, as well  as  compress  any  image  HDUs.  This
              option is intended for experimental use.

       -tableonly
              Compress  only  FITS  binary  tables  using prototype method; do not compress any image HDUs. This
              option is intended for experimental use.

       -F     Overwrite input file by output file with same name.

       -D     Delete input file after writing output.

       -Y     Suppress prompts to confirm -F or -D options.

       -S     Output compressed FITS files to STDOUT.

       -L     List contents; files unchanged.

       -C     Don't update FITS checksum keywords.

       -H     Show this message.

       -V     Show version number.

SEE ALSO

       funpack(1), fitscopy(1).