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.Id $Id: mgfelics.1 3745 2003-02-20 21:20:24Z mdewsnip $
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.TH mgfelics 1 \*(Dt CITRI
.SH NAME
mgfelics \- fast and efficient lossless image (de)compression
.SH SYNOPSIS
.B mgfelics
.B \-e
[
.BI \-k " n"
]
.I infile
[
.I \>compressed-outfile
]
.br
or
.br
.B mgfelics
.B \-d
.I compressed-infile
[
.I \>outfile
]
.SH DESCRIPTION
.B mgfelics
is a lossless compression process which can (de)compress portable
bitmap files in
.I pgm
format.
.B mgfelics
writes to
.IR stdout .
.SH OPTIONS
.TP "\w'\fB\-k\fP \fIn\fP'u+2n"
.BI \-k " n"
An integer parameter (< 32) which controls the compression speed and
ratio.  The value of
.I n
is included in the output stream, and therefore is not needed in the
decompression stage.  The default value of
.I n
is equal to the number of bits required to represent each grey level.
.TP
.B \-e
Encodes the file
.IR infile ,
sending the output to
.IR stdout .
.TP
.B \-d
Decodes the file from
.IR compressed-infile ,
sending the output to
.IR stdout .
.SH NOTE
.B mgfelics
uses a combination of adjusted binary and Rice codes, the choice of
which for any given pixel depends on the environment as determined by
the intensity values of neighbouring pixels.  The result is a very
fast and lossless algorithm for compressing grayscale images.  The
optional parameter
.BI \-k " n"
corresponds to the maximum exponent of the same name in Rice encoding.
Smaller values of
.BI \-k " n"
can result in significant improvement in compression times with a
corresponding loss in compression ratio.  However the reduction in
compression ratio with a small
.BI \-k " n"
parameter may be insignificant for many images.
.SH REFERENCES
Algorithm by Paul G. Howard and Jeffrey Scott Vitter
of Brown University, RI, and Duke University, NC, respectively.
.SH "SEE ALSO"
.na
.BR mg (1),
.BR mg_compression_dict (1),
.BR mg_fast_comp_dict (1),
.BR mg_get (1),
.BR mg_invf_dict (1),
.BR mg_invf_dump (1),
.BR mg_invf_rebuild (1),
.BR mg_passes (1),
.BR mg_perf_hash_build (1),
.BR mg_text_estimate (1),
.BR mg_weights_build (1),
.BR mgbilevel (1),
.BR mgbuild (1),
.BR mgdictlist (1),
.BR mgquery (1),
.BR mgstat (1),
.BR mgtic (1),
.BR mgticbuild (1),
.BR mgticdump (1),
.BR mgticprune (1),
.BR mgticstat (1).