NAME

       pbmreduce - read a PBM image and reduce it N times

SYNOPSIS

       pbmreduce [-floyd|-fs|-threshold] [-value val] [-randomseed=integer] N [pbmfile]

       You can abbreviate any option to its shortest unique prefix.

DESCRIPTION

       This program is part of Netpbm(1).

       pbmreduce reads a PBM image as input and reduces it by a factor of N, producing a PBM image as output.

       pbmreduce  duplicates  a  lot of the functionality of pamditherbw; you could do something like pamscale |
       pamditherbw, but pbmreduce is a lot faster.

       You can use pbmreduce 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 pbmreduce.  You can even correct the brightness of an
       image, by using the -value option.

OPTIONS

       In addition to the options common to all programs based on libnetpbm (most notably  -quiet,  see   Common
       Options ), pbmreduce recognizes the following command line options:

       -threshold
              By  default, pbmreduce does the halftoning after the reduction via boustrophedonic Floyd-Steinberg
              error diffusion; however, you can use this option to  specify  simple  thresholding.   This  gives
              better results when reducing line drawings.

       -floyd, -fs
              Specify the Floyd-Steinberg error diffusion method.  This is the default.

       -value

              This  option  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.

       -randomseed=integer
              This is the seed for the random number generator that controls the halftoning.

              Use this to ensure you get the same image on separate invocations.

              This option was new in Netpbm 10.75 (June 2016).

SEE ALSO

       pamenlarge(1), pamscale(1), pamditherbw(1), pbm(1)

AUTHOR

       Copyright (C) 1988 by Jef Poskanzer.

DOCUMENT SOURCE

       This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The  master  documentation
       is at

              http://netpbm.sourceforge.net/doc/pbmreduce.html

netpbm documentation                              13 April 2016                         Pbmreduce User Manual(1)