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Pnmshear User Manual(0) 						  Pnmshear User Manual(0)

NAME
       pnmshear - shear a PNM image by a specified angle

SYNOPSIS
       pnmshear

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

       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.

DESCRIPTION
       This program is part of Netpbm(1)

       pnmshear reads a PNM image as input and shears it by the specified angle and produce a PNM
       image 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), and measures this:

	   +-------+  +-------+
	   |	   |  |\       \
	   |  OLD  |  | \  NEW	\
	   |	   |  |an\	 \
	   +-------+  |gle+-------+

       If the angle is negative, it shears the other way:
	   +-------+  |-an+-------+
	   |	   |  |gl/	 /
	   |  OLD  |  |e/  NEW	/
	   |	   |  |/       /
	   +-------+  +-------+

       The  angle should not get too close to 90 or -90, or the resulting image will be unreason-
       ably wide.

       pnmshear does the shearing 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 in the image
       are  modified  and there are typically more of them than you started with.  If you need to
       keep precisely the same set of colors, see the -noantialias option.  If the expanded  pal-
       ette is a problem, you can run the result through pnmquant.

OPTIONS
       -background=color
	      This determines the color of the background on which the sheared 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, pnmshear 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
	      image.

	      This  option was new in Netpbm 10.37 (December 2006).  Before that, pnmshear always
	      behaved as is the default now.

       -noantialias
	      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.

SEE ALSO
       pnmrotate(1) , pamflip(1) , pnmquant(1) , pnm(1)

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

netpbm documentation			 27 November 2006		  Pnmshear User Manual(0)
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