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Pbmreduce User Manual(0)			      Pbmreduce	User Manual(0)

NAME
       pbmreduce - read	a PBM image and	reduce it N times

SYNOPSIS
       pbmreduce  [-floyd|-fs|-threshold] [-value val] N [-randomseed=integer]
       [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	 reso-
       lution,	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
       -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.

       -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 invoca-
	      tions.

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

SEE ALSO
       pamenlarge(1), pamscale(1), pamditherbw(1), pbm(5)

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(0)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SEE ALSO | AUTHOR | DOCUMENT SOURCE

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