pnmrotate(1)             USER COMMANDS               pnmrotate(1)



NAME
     pnmrotate - rotate a portable anymap by some angle

SYNOPSIS
     pnmrotate [-noantialias] _a_n_g_l_e [_p_n_m_f_i_l_e]

DESCRIPTION
     Reads a portable anymap as input.  Rotates it by the  speci-
     fied 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 degrees you may get better  results  if  you
     first use _p_n_m_f_l_i_p to do a 90 degree rotation and then _p_n_m_r_o_-
     _t_a_t_e 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  pix-
     els.   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 modi-
     fied.  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 _p_p_m_q_u_a_n_t.

     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.













Sun Release 4.0   Last change: 12 January 1991                  1