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pnmrotate.1
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1995-07-25
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ppppnnnnmmmmrrrroooottttaaaatttteeee((((1111)))) XXXXEEEENNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((11112222 JJJJaaaannnnuuuuaaaarrrryyyy 1111999999991111)))) ppppnnnnmmmmrrrroooottttaaaatttteeee((((1111))))
NNNNAAAAMMMMEEEE
pnmrotate - rotate a portable anymap by some angle
SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
ppppnnnnmmmmrrrroooottttaaaatttteeee [----nnnnooooaaaannnnttttiiiiaaaalllliiiiaaaassss] _a_n_g_l_e [_p_n_m_f_i_l_e]
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
Reads a portable anymap as input. Rotates 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), 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 _p_n_m_f_l_i_p to do a 90 degree rotation and then
_p_n_m_r_o_t_a_t_e 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
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 ----nnnnooooaaaannnnttttiiiiaaaalllliiiiaaaassss 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 _p_p_m_q_u_a_n_t.
All flags can be abbreviated to their shortest unique
prefix.
RRRREEEEFFFFEEEERRRREEEENNNNCCCCEEEESSSS
"A Fast Algorithm for General Raster Rotation" by Alan
Paeth, Graphics Interface '86, pp. 77-81.
SSSSEEEEEEEE AAAALLLLSSSSOOOO
pnmshear(1), pnmflip(1), pnm(5), ppmquant(1)
AAAAUUUUTTTTHHHHOOOORRRR
Copyright (C) 1989, 1991 by Jef Poskanzer.
Page 1 (printed 9/7/93)