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pbmreduce.1
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1995-07-25
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3KB
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67 lines
ppppbbbbmmmmrrrreeeedddduuuucccceeee((((1111)))) XXXXEEEENNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((00002222 AAAAuuuugggguuuusssstttt 1111999988889999)))) ppppbbbbmmmmrrrreeeedddduuuucccceeee((((1111))))
NNNNAAAAMMMMEEEE
pbmreduce - read a portable bitmap and reduce it N times
SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
ppppbbbbmmmmrrrreeeedddduuuucccceeee [----ffffllllooooyyyydddd|----ffffssss|----tttthhhhrrrreeeesssshhhhoooolllldddd ] [----vvvvaaaalllluuuueeee _v_a_l] _N [_p_b_m_f_i_l_e]
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
Reads a portable bitmap as input. Reduces it by a factor of
_N, and produces a portable bitmap as output.
_p_b_m_r_e_d_u_c_e duplicates a lot of the functionality of _p_g_m_t_o_p_b_m;
you could do something like ppppnnnnmmmmssssccccaaaalllleeee |||| ppppggggmmmmttttooooppppbbbbmmmm,,,, but
_p_b_m_r_e_d_u_c_e is a lot faster.
_p_b_m_r_e_d_u_c_e can be used to "re-halftone" an image. Let's say
you have a scanner that only produces black&white, not
grayscale, and it does a terrible job of halftoning (most
b&w scanners fit this description). One way to fix the
halftoning is to scan at the highest possible resolution,
say 300 dpi, and then reduce by a factor of three or so
using _p_b_m_r_e_d_u_c_e. You can even correct the brightness of an
image, by using the ----vvvvaaaalllluuuueeee flag.
OOOOPPPPTTTTIIIIOOOONNNNSSSS
By default, the halftoning after the reduction is done via
boustrophedonic Floyd-Steinberg error diffusion; however,
the ----tttthhhhrrrreeeesssshhhhoooolllldddd flag can be used to specify simple
thresholding. This gives better results when reducing line
drawings.
The ----vvvvaaaalllluuuueeee flag alters the thresholding value for all
quantizations. It should be a real number between 0 and 1.
Above 0.5 means darker images; below 0.5 means lighter.
All flags can be abbreviated to their shortest unique
prefix.
SSSSEEEEEEEE AAAALLLLSSSSOOOO
pnmenlarge(1), pnmscale(1), pgmtopbm(1), pbm(5)
AAAAUUUUTTTTHHHHOOOORRRR
Copyright (C) 1988 by Jef Poskanzer.
Page 1 (printed 9/7/93)