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1995-03-17
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pnmshear(1) AMIGA (12 January 1991) 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 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.
Page 1 (printed 10/19/91)