PNMSHEAR

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.

DEMONSTRATION

      Let a.pnm be a portable anymap.
      The following command will shear it by an angle of 32 degrees:
	pnmmerge pnmshear 32 a.pnm > ashear.pnm

BEFORE

AFTER

SEE ALSO

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

AUTHOR

      Copyright (C) 1989, 1991 by Jef Poskanzer.