\
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.TH "Ppmshift User Manual" 0 "20 November 2008" "netpbm documentation"

.SH NAME

ppmshift - shift lines of a PPM image left or right by a random amount

.UN synopsis
.SH SYNOPSIS

\fBppmshift\fP
\fIshift\fP
[\fIppmfile\fP]

.UN description
.SH DESCRIPTION
.PP
This program is part of
.BR Netpbm (1)
.
.PP
\fBppmshift\fP reads a PPM image as input.  Shifts every row of image data
to the left or right by a random amount, within a range of \fIshift\fP
pixels.  The random distribution is uniform, centered at zero movement.
.PP
The randomness in the image is limited before Netpbm 10.37 (December
2006) -- if you run the program twice in the same second, you may get
identical output.
.PP
This is another one of those effects I intended to use for MPEG
tests.  Unfortunately, this program will not help me here - it creates
too random patterns to be used for animations.  Still, it might give
interesting results on still images.

.UN example
.SH EXAMPLE
.PP
Check this out: Save your favourite model's picture from something like
alt.binaries.pictures.supermodels (ok, or from any other picture source),
convert it to ppm, and process it e.g. like this, assuming the picture is 
800x600 pixels:

.nf
     #take the upper half, and leave it like it is
     pamcut -top=0 -width=800 -height=300 cs.ppm >upper.ppm
     
     #take the lower half, flip it upside down, dim it and distort it a little
     pamcut -top=300 -width=800 -height=300 cs.ppm | \e
         pamflip -topbottom | \e
         ppmdim 0.7 | \e
         ppmshift 10 >lower.ppm
     
     #and concatenate the two pieces
     pnmcat -topbottom upper.ppm lower.ppm >newpic.ppm

.fi
.PP
The resulting picture looks like the image being reflected on a water 
surface with slight ripples.

.UN seealso
.SH SEE ALSO
.BR ppm (5)
,
.BR pamcut (1)
,
.BR pamflip (1)
,
.BR ppmdim (1)
,
.BR pnmcat (1)



.UN author
.SH AUTHOR

Copyright (C) 1993 by Frank Neumann