.TL
Pnmshear User Manual
.SH 1
pnmshear
.LP
Updated: 12 January 1991
.br
Table Of Contents
.SH 2
NAME
.LP
pnmshear - shear a PNM image by a specified angle
.SH 2
SYNOPSIS
.LP
\fBpnmshear\fR
[\fB-noantialias\fR]
\fIangle\fR
[\fIpnmfile\fR]
.SH 2
DESCRIPTION
.LP
.LP
This program is part of Netpbm.
.LP
\fBpnmshear\fR 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:
.DS L
    +-------+  +-------+
    |       |  |\       \
    |  OLD  |  | \  NEW  \
    |       |  |an\       \
    +-------+  |gle+-------+
.DE
If the angle is negative, it shears the other way:
.DS L
    +-------+  |-an+-------+
    |       |  |gl/       /
    |  OLD  |  |e/  NEW  /
    |       |  |/       /
    +-------+  +-------+
.DE
The angle should not get too close to 90 or -90, or the resulting
anymap will be unreasonably wide.
.LP
\fBpnmshear\fR does the shearing 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 \fB-noantialias\fR 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 *number* of colors, you can run the result
through \fBpnmquant\fR.
.LP
All options can be abbreviated to their shortest unique prefix.
.SH 2
SEE ALSO
.LP
pnmrotate,
pamflip,
pnmquant,
pnm
.SH 2
AUTHOR
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Copyright (C) 1989, 1991 by Jef Poskanzer.
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\l'5i'
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Table Of Contents
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