pnmshear



Pnmshear User Manual(0)                                Pnmshear User Manual(0)




NAME

       pnmshear - shear a PNM image by a specified angle



SYNOPSIS

       pnmshear

       [-noantialias]

       angle

       [pnmfile]



DESCRIPTION

       This program is part of Netpbm(1).

       pnmshear  reads  a  PNM  image  as input and shears it by the specified
       angle and produce a PNM image 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.

       pnmshear  does  the shearing 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 option.  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 *num-
       ber* of colors, you can run the result through pnmquant.

       All options can be abbreviated to their shortest unique prefix.



SEE ALSO

       pnmrotate(1), pamflip(1), pnmquant(1), pnm(1)




AUTHOR

       Copyright (C) 1989, 1991 by Jef Poskanzer.



netpbm documentation            12 January 1991        Pnmshear User Manual(0)

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