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.\" wm_cox_d.1 - the *roff document processor man page source
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.TH wm_cox_d 1 "98/07/05" "Watermarking, Version 1.0"
.SH NAME
.B wm_cox_d
\- a program to extract a signature from the DCT coefficients of a watermarked image
.SH SYNOPSIS
.B wm_cox_d
[
.BI \-a \ number
]
[
.B \-h
]
[
.BI \-i \ ifile
]
[
.BI \-n \ number
]
[
.BI \-o \ ofile
]
[
.BI \-q \ number
]
[
.BI \-v \ number
]
.br
.BI \-s \ sfile
.I file
.SH DESCRIPTION
.B wm_cox_d
is a program to extract a signature from the DCT coefficients of the watermarked image
.I file.
The
.B cmp_cox_sig
program is used to test the extracted signature against the original signature.
The input image is in PGM (portable graymap) format.
.PP
If
.I file
or
.I ofile
is not specified, then standard input or standard output is
used.
.PP
.B gen_cox_sig
is used to generate a signature file,
.B wm_cox_e
embeds the signature into an image.
.PP
Please refer to Ingemar J. Cox's paper "Secure Spread Spectrum
Watermarking for Multimedia", 1995, to get an idea about the algorithm.
.PP
.SH OPTIONS
.TP
.BI \-a \ number
Alpha factor that determines embedding strength of the signature.
Allows to override the setting in the signature file.
.TP
.B \-h
Print a help message.
.TP
.BI \-i \ ifile
The original image.
.TP
.BI \-o \ ofile
Output watermarked image to the specified
.I file
instead of standard output.
.TP
.BI \-q \ number
Set quantization/quality factor. Overrides the setting in the signature
file.
.TP
.BI \-v \ number
Verbosity level. Default value: 0.
.TP
.BI \-s \ sfile
The signature file to embed into the input image. See
.B gen_cox_sig
(1) for a description of the file format. Mandatory parameter.
.IR file
Input image in PGM format to sign (watermark). Default: standard input.
.TP
.I
The watermarked image file in PGM format.
.PP
.SH OUTPUT
The signed (watermarked) image in PGM format is written to standard output
or ,optionally, to
.I ofile.
The embedding process may take some time on large images since the DCT
is performed on the whole image in one step (not block-wise).
.PP
.PP
The output file has the following format:
.TP
.B CXSG
Magic to identify file type.
.TP
.I number
The length of the signature in bits.
.TP
.I number
The alpha factor (embedding strength).
.TP
.I number
The quantization/quality factor.
.TP
.I numbers
The actual normal distributed signature values, one per line.
.PP
.SH AUTHOR
Peter Meerwald. 
Email bug reports to pmeerw@cosy.sbg.ac.at.
.SH AVAILABILITY
The most recent released version of
.B wm_cox_d
is always available
at http://www.cosy.sbg.ac.at/~pmeerw/Watermarking or via anonymous ftp from ftp.cosy.sbg.ac.at in the
directory /pub/people/pmeerw/Watermarking.
.SH "SEE ALSO"
.BR gen_cox_sig
(1),
.BR wm_cox_e
(1),
.BR cmp_cox_sig
(1)