.\"
.\" wm_koch_d.1 - the *roff document processor man page source
.\"
.TH wm_koch_d 1 "98/07/05" "Watermarking, Version 1.0"
.SH NAME
.B wm_koch_d
\- a program to extract signature bits that have been embedded into
the DCT coefficients of an image
.SH SYNOPSIS
.B wm_koch_d
[
.B \-h
]
[
.BI \-o \ ofile
]
[
.BI \-q \ number
]
[
.BI \-v \ number
]
.BI \-s \ sfile
.IR file
.SH DESCRIPTION
.B wm_koch_d
is a program to extract signature bits from the 8x8 DCT coefficients of
an image, embedded with the
.B wm_koch_e
watermarking program.
.B cmp_koch_sig
program compares and tests the extracted signature against the original signature.
.PP
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. The signature
.I sfile
is a mandatory parameter however.
.PP
Please refer to E. Koch's paper "Towards Robust and Hidden
Image Copyright", 1995, to get an idea about the algorithm.
.PP
.SH OPTIONS
.TP
.B \-h
Print a help message.
.TP
.BI \-o \ ofile
Output the extracted signature to
.I ofile
instead of standard output.
.TP
.BI \-q \ number
Quality/robustness factor used to extract the signature.
Overrides setting from signature file.
.TP
.BI \-s \ sfile
The original signature file. See
.B gen_koch_sig
(1) for a description of the file format. Mandatory parameter.
.BI \-v \ number
Verbosity level. 0 for quiet operation, higher numbers for more 
output. Default value: 0.
.TP
.IR file
Signed (watermarked) input image in PGM format. Default: standard input.
.PP
.SH OUTPUT
The extracted signature is written to standard output
or, optionally, to
.I ofile.
.PP
The extraction algorithm examines the relationship between two random
coefficients of randomly selected 8x8 DCT blocks to reconstruct the
signature bits.
.PP
The output file has the following format:
.TP
.B KCSG
Magic to identify file type.
.TP
.I number
The length of the signature in bits.
.TP
.I number
The quality/robustness factor.
.TP
.I number
The seed value for the pseudo-random number generator.
.TP
.I string
The actual signature bytes.
.PP
.SH AUTHOR
Peter Meerwald. 
Email bug reports to pmeerw@cosy.sbg.ac.at.
.SH AVAILABILITY
The most recent released version of
.B wm_koch_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_koch_sig
(1),
.BR wm_koch_e
(1),
.BR cmp_koch_sig
(1)