NAME

       fpack - FITS image compression program

SYNOPSYS

       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).