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.

Amiga Unix  —  Last change: 15 February 1989