pnmshear(1)

NAME

   pnmshear - shear a portable anymap by some angle

SYNOPSIS

   pnmshear [-noantialias] angle [pnmfile]

DESCRIPTION

   Reads a portable anymap as input.  Shears 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), 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
   anymap will be unreasonably wide.

   The  shearing  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.

SEE ALSO

   pnmrotate(1), pnmflip(1), pnm(5), ppmquant(1)

AUTHOR

   Copyright (C) 1989, 1991 by Jef Poskanzer.

                            12 January 1991                    pnmshear(1)

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Free and Open Source Software