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1995-02-13
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ppmrotate(1) PBM Plus ppmrotate(1)
NAME
ppmrotate - rotate a portable pixmap by some angle
SYNOPSIS
ppmrotate angle [ppmfile]
DESCRIPTION
Reads a portable pixmap as input. Rotates it by the speci-
fied angle and produces a portable pixmap as output. The
angle is in degrees (floating point), measured counter-
clockwise. It can be negative, but it should be between -90
and 90.
The rotation algorithm is Alan Paeth's three-shear method.
Each shear is implemented by looping over the source pixels
and distributing fractions to each of the destination pix-
els.
REFERENCES
"A Fast Algorithm for General Raster Rotation" by Alan
Paeth, Graphics Interface '86, pp. 77-81.
SEE ALSO
ppmshear(1), pnmflip(1), ppm(5)
AUTHOR
Copyright (C) 1989 by Jef Poskanzer.
Permission to use, copy, modify, and distribute this
software and its documentation for any purpose and without
fee is hereby granted, provided that the above copyright
notice appear in all copies and that both that copyright
notice and this permission notice appear in supporting docu-
mentation. This software is provided "as is" without
express or implied warranty.
Printed 5/25/90 15 February 1989 1