pnmrotate(1) - man - phpMan

pnmrotate(1)                           General Commands Manual                          pnmrotate(1)



NAME
       pnmrotate - rotate a portable anymap by some angle

SYNOPSIS
       pnmrotate [-noantialias] angle [pnmfile]

DESCRIPTION
       Reads  a portable anymap as input.  Rotates it by the specified angle and produces a portable
       anymap as output.  If the input file is in color, the output will be too, otherwise  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  de‐
       grees you may get better results if you first use pnmflip to do a 90 degree rotation 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 pixels 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 values.  If you want anti-aliasing and don't
       care about the precise colors, but still need a limited *number* of colors, you can  run  the
       result through ppmquant.

       All flags can be abbreviated to their shortest unique prefix.

REFERENCES
       "A  Fast  Algorithm  for  General Raster Rotation" by Alan Paeth, Graphics Interface '86, pp.
       77-81.

SEE ALSO
       pnmshear(1), pnmflip(1), pnm(5), ppmquant(1)

AUTHOR
       Copyright (C) 1989, 1991 by Jef Poskanzer.



                                           12 January 1991                              pnmrotate(1)