pnmshear(1)                                                   General Commands Manual                                                  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 lim-
       ited *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)