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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)