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+.\"
+.\" cmp_ppm.1 - the *roff document processor man page source
+.\"
+.TH cmp_ppm 1 "98/07/08" "Watermarking, Version 1.0"
+.SH NAME
+cmp_ppm \- a program to create the difference image of two PGM images
+.SH SYNOPSIS
+.B cmp_ppm
+[
+.BI \-c \ name
+]
+[
+.B \-h
+]
+[
+.BI \-m \ number
+]
+[
+.BI \-o \ ofile
+]
+.BI \-i \ ifile
+.I file
+.SH DESCRIPTION
+.B cmp_ppm
+is a program to create the difference image of two PPM (portable pixmap)
+RGB color images. To compare PGM (portable graymap) grayscale images, use
+the
+.B cmp_pgm
+program.
+.PP
+The color components to compare are specified with the
+.BI \-c \ name
+option, where
+.I name
+is one of the following:
+.TP
+.B red
+The red color component.
+.TP
+.B green
+The green color component.
+.TP
+.B blue
+The blue color component.
+.PP
+Multiple color components are allowed. Specifying only the inital letter
+of a color component is sufficient.
+Per default
+.B cmp_ppm
+compares the luminance value of the images. This operation may be
+selected explicitly with the
+.BI \-c \ luminance
+option.
+.PP
+If
+.I file
+or
+.I ofile
+is not specified, then standard input or standard output is
+used.
+.PP
+.SH OPTIONS
+.TP
+.BI \-c \ name
+Specifies color component(s) or luminance to compare. Default: luminance.
+.TP
+.B \-h
+Print a help message.
+.TP
+.BI \-i \ ifile
+The original image. Mandatory.
+.TP
+.BI \-m \ number
+Multiplication factor to magnify differences between the to
+original and input image.
+Default value: 16.
+.TP
+.BI \-o \ ofile
+Output image file to contain the difference image in PPM format.
+.TP
+.I file
+Input image that is compared against
+.I ifile.
+Default: standard input.
+.SH OUTPUT
+The difference image in PPM format is written to standard output or,
+optionally, to
+.I ofile.
+.SH AUTHOR
+Peter Meerwald.
+Email bug reports to pmeerw@cosy.sbg.ac.at.
+.SH AVAILABILITY
+The most recent released version of
+.B cmp_ppm
+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"
+.B cmp_ppm
+(1)