pnmshear(1)             UNIX System V(12 January 1991)              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.












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