Man Pages

pbmreduce(1) - phpMan pbmreduce(1) - phpMan

Command: man perldoc info search(apropos)  

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

       pbmreduce - read a PBM image and reduce it N times

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

       You can abbreviate any option to its shortest unique prefix.

       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.

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

       The  -value  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.

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

       Copyright (C) 1988 by Jef Poskanzer.

netpbm documentation            02 August 1989        Pbmreduce User Manual(0)