pnmshear

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 dis-
       tributing 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 col-
       ors, you can use the -noantialias flag.  This does the shearing by mov-
       ing  pixels  without  changing their values.  If you want anti-aliasing
       and don't care about the precise colors, but still need a limited *num-
       ber* 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)