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 ⟨index.html#commonoptions⟩ ), 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