pnmrotate(1) - phpMan

pnmrotate(1) General Commands Manual pnmrotate(1)

NAME
pnmrotate - rotate a portable anymap by some angle

SYNOPSIS
pnmrotate [-noantialias] angle [pnmfile]

DESCRIPTION
Reads a portable anymap as input. Rotates 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), measured counter-clockwise.
It can be negative, but it should be between -90 and 90. Also, for rotations greater than
45 degrees you may get better results if you first use pnmflip to do a 90 degree rotation
and then pnmrotate less than 45 degrees back the other direction

The rotation algorithm is Alan Paeth's three-shear method. Each shear is implemented by
looping over the source pixels and distributing fractions to each of the destination pix-
els. 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.

REFERENCES
"A Fast Algorithm for General Raster Rotation" by Alan Paeth, Graphics Interface '86, pp.
77-81.

SEE ALSO
pnmshear(1), pnmflip(1), pnm(5), ppmquant(1)

12 January 1991 pnmrotate(1)

Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2024-04-19 16:41 @3.17.150.163 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)