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pnmshear - shear a portable anymap by some angle
pnmshear [-noantialias] angle [pnmfile]
Reads a portable anymap as input. Shears it by the specified angle and produces a porta-
ble 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\ \
If the angle is negative, it shears the other way:
| | |gl/ /
| OLD | |e/ NEW /
| | |/ /
The angle should not get too close to 90 or -90, or the resulting anymap will be unreason-
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 lev-
els 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.
pnmrotate(1), pnmflip(1), pnm(5), ppmquant(1)
Copyright (C) 1989, 1991 by Jef Poskanzer.
12 January 1991 pnmshear(1)
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