PPMROTATE

NAME

      ppmrotate - rotate a portable pixmap by some angle

SYNOPSIS

      ppmrotate angle [ppmfile]

DESCRIPTION

      Reads a portable pixmap as input.  Rotates it by the specified 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 pixels.

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 documentation.  This software is provided "as is" without
      express or implied warranty.