home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Mega A/V
/
mega_av.zip
/
mega_av
/
GRAPHUTL
/
PBMPLUS.ZIP
/
PBMREDUC.MAN
< prev
next >
Wrap
Text File
|
1991-08-11
|
2KB
|
67 lines
pbmreduce(1) Unix Programmer's Manual pbmreduce(1)
NNNAAAMMMEEE
pbmreduce - read a portable bitmap and reduce it N times
SSSYYYNNNOOOPPPSSSIIISSS
pppbbbmmmrrreeeddduuuccceee [-fffllloooyyyddd|-fffsss|-ttthhhrrreeessshhhooolllddd] [-vvvaaallluuueee _v_a_l] _N [_p_b_m_f_i_l_e]
DDDEEESSSCCCRRRIIIPPPTTTIIIOOONNN
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 pppnnnmmmssscccaaallleee ||| pppgggmmmtttooopppbbbmmm,,, 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 ---vvvaaallluuueee
flag.
OOOPPPTTTIIIOOONNNSSS
By default, the halftoning after the reduction is done via
boustrophedonic Floyd-Steinberg error diffusion; however, the ---ttthhhrrreeessshhhooolllddd
flag can be used to specify simple thresholding. This gives better
results when reducing line drawings.
The ---vvvaaallluuueee 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.
SSSEEEEEE AAALLLSSSOOO
pnmenlarge(1), pnmscale(1), pgmtopbm(1), pbm(5)
AAAUUUTTTHHHOOORRR
Copyright (C) 1988 by Jef Poskanzer.
02 August 1989 1