pnmrotate

 

---

 pnmrotate(1)                                         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 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 ALSO
        pnmshear(1), pnmflip(1), pnm(5), ppmquant(1)
 
AUTHOR
        Copyright (C) 1989, 1991 by Jef Poskanzer.
 
 
 
                          12 January 1991             pnmrotate(1)

---