pnmrotate(1)pnmrotate(1)NAMEpnmrotate - rotate a portable anymap by some angle
SYNOPSISpnmrotate [-noantialias] angle [pnmfile]
DESCRIPTION
Reads a portable anymap as input. Rotates it by the spec
ified angle and produces a portable anymap as output. If
the input file is in color, the output will be too, other
wise it will be grayscale. The angle is in degrees
(floating point), measured counter-clockwise. It can be
negative, but it should be between -90 and 90. Also, for
rotations greater than 45 degrees you may get better
results if you first use pnmflip to do a 90 degree rota
tion and then pnmrotate less than 45 degrees back the
other direction
The rotation algorithm is Alan Paeth's three-shear method.
Each shear is implemented by looping over the source pix
els and distributing fractions to each of the destination
pixels. This has an "anti-aliasing" effect - it avoids
jagged edges and similar artifacts. However, it also
means that the original colors or gray levels in the image
are modified. If you need to keep precisely the same set
of colors, you can use the -noantialias flag. This does
the shearing by moving pixels without changing their val
ues. If you want anti-aliasing and don't care about the
precise colors, but still need a limited *number* of col
ors, you can run the result through ppmquant.
All flags can be abbreviated to their shortest unique pre
fix.
REFERENCES
"A Fast Algorithm for General Raster Rotation" by Alan
Paeth, Graphics Interface '86, pp. 77-81.
SEE ALSOpnmshear(1), pnmflip(1), pnm(5), ppmquant(1)AUTHOR
Copyright (C) 1989, 1991 by Jef Poskanzer.
12 January 1991 pnmrotate(1)
