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Pnmrotate User Manual(0)						 Pnmrotate User Manual(0)

       pnmrotate - rotate a PNM image by some angle

       pnmrotate [-noantialias] [-background=color] angle [pnmfile]

       This program is part of Netpbm(1)

       pnmrotate  reads  a PNM image as input.	It rotates it by the specified angle and produces
       the same kind of PNM image as output.

       The input is the file named by pnmfile or Standard Input if  you  don't	specify  pnmfile.
       The output goes to Standard Output.

       The  resulting image is a rectangle that contains the (rectangular) input image within it,
       rotated with respect to its bottom edge.  The containing rectangle is as small as possible
       to  contain  the  rotated image.  The background of the containing image is a single color
       that pnmrotate determines to be the background color of the original image,  or	that  you
       specify explicitly.

       angle is in decimal degrees (floating point), measured counter-clockwise.  It can be nega-
       tive, but it should be between -90 and 90.

       You should use pamflip instead for rotations that are a multiple of a quarter turn.  It is
       faster and more accurate.

       For  rotations greater than 45 degrees you may get better results if you first use pamflip
       to do a 90 degree rotation and then pnmrotate less than 45 degrees back the  other  direc-

       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	modified.
       If you need to keep precisely the same set of colors, you can use the -noantialias option.

       The program runs faster and uses less real memory with the -noantialias option.	It uses a
       large amount of virtual memory either way, as it keeps a copy of the  input  image  and	a
       copy  of  the  output image in memory, using 12 bytes per pixel for each.  But with -noan-
       tialias, it accesses this memory sequentially in half a dozen  passes,  with  only  a  few
       pages of memory at a time required in real memory.

       In  contrast, without -noantialias, the program's real memory working set size is one page
       per input image row plus one page per output image row.	Before Netpbm 10.16 (June  2003),
       -noantialias had the same memory requirement.

       All  options  can be abbreviated to their shortest unique prefix.  You may use two hyphens
       instead of one to designate an option.  You may use either white  space	or  equals  signs
       between an option name and its value.

	      This determines the color of the background on which the rotated image sits.

	      Specify  the  color  (color)  as described for the argument of the ppm_parsecolor()
	      library routine <libppm.html#colorname> .

	      By default, if you don't specify this option, pnmrotate selects what appears to  it
	      to  be the background color of the original image.  It determines this color rather
	      simplistically, by taking an average of the colors of the two top  corners  of  the

	      This  option  was new in Netpbm 10.15.  Before that, pnmrotate always behaved as is
	      the default now.

	      This option forces pnmrotate to simply move pixels around instead  of  synthesizing
	      output  pixels  from  multiple  input pixels.  The latter could cause the output to
	      contain colors that are not in the input, which may  not	be  desirable.	 It  also
	      probably	makes  the  output contain a large number of colors.  If you need a small
	      number of colors, but it doesn't matter if they are the exact ones from the  input,
	      consider using pnmquant on the output instead of using -noantialias.

	      Note  that  to ensure the output does not contain colors that are not in the input,
	      you also must consider the background color.  See the -background option.

       'A Fast Algorithm for General Raster Rotation' by Alan Paeth, Graphics Interface '86,  pp.

       pnmshear(1) , pamflip(1) , pnmquant(1) , pnm(1)

       Copyright (C) 1989, 1991 by Jef Poskanzer.

netpbm documentation			  30 August 2002		 Pnmrotate User Manual(0)
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