127 lines
4.1 KiB
Groff
127 lines
4.1 KiB
Groff
.TH fpack "1" "April 2014" "CFITSIO version 3.370" "User Commands"
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.SH NAME
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fpack \- FITS image compression program
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.SH SYNOPSIS
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.B funpack
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[\fIOPTION\fR]... \fIFILE\fR...
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.SH DESCRIPTION
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.PP
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.B fpack
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is a utility program for optimally compressing images in the FITS data format.
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This programs is analogous to the GZIP utility program except that it is
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optimized for FITS format images and offer a wider choice of compression
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options.
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.SH OPTIONS
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.PP
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Flags must be separate and appear before filenames. Use '\-' to read from stdin.
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.PP
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The compression parameters specified on the \fBfpack\fR command line may
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be overridden by compression directive keywords in the header of each HDU
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of the input file(s).
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.TP
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\fB\-r\fR
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Rice compression (default).
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.TP
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\fB\-h\fR
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Hcompress compression.
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.TP
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\fB\-g\fR
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or \fB\-g1\fR GZIP_1 (per\-tile) compression.
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.TP
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\fB\-g2\fR
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GZIP_2 (per\-tile) compression (with byte shuffling).
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.TP
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\fB\-p\fR
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PLIO compression (only for positive 8 or 16\-bit integer images).
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.TP
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\fB\-d\fR
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Tile the image without compression (debugging mode).
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.TP
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\fB\-w\fR
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Compress the whole image as a single large tile.
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.TP
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\fB\-t\fR \fIaxes\fR
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Comma separated list of tile dimensions (default is row by row).
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.TP
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\fB\-q\fR \fIlevel\fR
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Quantized level spacing when converting floating point images to
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scaled integers. (+value relative to sigma of background noise;
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\fB\-value\fR is absolute). Default q value of 4 gives a compression ratio
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of about 6 with very high fidelity (only 0.26% increase in noise).
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Using q values of 2, or 1 will give compression ratios of
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about 8, or 10, respectively (with 1.0% or 4.1% noise increase).
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The scaled quantized values are randomly dithered using a seed
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value determined from the system clock at run time.
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Use \fB\-q0\fR instead of \fB\-q\fR to suppress random dithering.
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Use \fB\-qz\fR instead of \fB\-q\fR to not dither zero\-valued pixels.
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Use \fB\-qt\fR or \fB\-qzt\fR to compute random dithering seed from first tile checksum.
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Use \fB\-qN\fR or \fB\-qzN\fR, (N in range 1 to 10000) to use a specific dithering seed.
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Floating\-point images can be losslessly compressed by selecting
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the GZIP algorithm and specifying \fB\-q\fR 0, but this is slower and often
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produces much less compression than the default quantization method.
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.TP
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\fB\-i2f\fR
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Convert integer images to floating point, then quantize and compress
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using the specified q level. When used appropriately, this lossy
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compression method can give much better compression than the normal
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lossless compression methods without significant loss of information.
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The \fB\-n3ratio\fR and \fB\-n3min\fR flags control the minimum noise thresholds;
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Images below these thresholds will be losslessly compressed.
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.TP
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\fB\-n3ratio\fR
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Minimum ratio of background noise sigma divided by q. Default = 2.0.
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.TP
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\fB\-n3min\fR
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Minimum background noise sigma. Default = 6. The \fB\-i2f\fR flag will be ignored
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if the noise level in the image does not exceed both thresholds.
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.TP
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\fB\-s\fR \fIscale\fR
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Scale factor for lossy Hcompress (default = 0 = lossless)
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(+values relative to RMS noise; \fB\-value\fR is absolute)
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.TP
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\fB\-n\fR \fInoise\fR
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Rescale scaled\-integer images to reduce noise and improve compression.
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.TP
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\fB\-v\fR
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Verbose mode; list each file as it is processed.
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.TP
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\fB\-T\fR
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Show compression algorithm comparison test statistics; files unchanged.
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.TP
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\fB\-R\fR \fIfile\fR
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Write the comparison test report (above) to a text file.
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.TP
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\fB\-table\fR
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Compress FITS binary tables using prototype method, as well as compress
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any image HDUs. This option is intended for experimental use.
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.TP
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\fB\-tableonly\fR
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Compress only FITS binary tables using prototype method; do not compress
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any image HDUs. This option is intended for experimental use.
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.TP
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\fB\-F\fR
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Overwrite input file by output file with same name.
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.TP
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\fB\-D\fR
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Delete input file after writing output.
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.TP
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\fB\-Y\fR
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Suppress prompts to confirm \fB\-F\fR or \fB\-D\fR options.
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.TP
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\fB\-S\fR
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Output compressed FITS files to STDOUT.
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.TP
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\fB\-L\fR
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List contents; files unchanged.
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.TP
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\fB\-C\fR
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Don't update FITS checksum keywords.
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.TP
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\fB\-H\fR
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Show this message.
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.TP
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\fB\-V\fR
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Show version number.
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.SH "SEE ALSO"
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\fBfunpack\fP(1), \fBfitscopy\fP(1).
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