pgmtopbm

pgmtopbm(1)                 General Commands Manual                pgmtopbm(1)

NAME
       pgmtopbm - convert a portable graymap into a portable bitmap

SYNOPSIS
       pgmtopbm   [-floyd|-fs|-threshold   |-hilbert   |-dither8|-d8|-cluster3
       |-c3|-cluster4|-c4 |-cluster8|-c8] [-value val] [-clump size] [pgmfile]

DESCRIPTION
       Reads a portable graymap as input.  Produces a portable bitmap as  out-
       put.

       Note  that  there  is no pbmtopgm converter.  Any program that uses the
       Netpbm libraries to read PGM files, including virtually all programs in
       the  Netpbm package, will read a PBM file automatically as if it were a
       PGM file.

       If you are using a less intelligent program that expects PGM input, use
       pnmdepth  to  convert  the  PBM  file  to PGM.  As long as the depth is
       greater than 1, pnmdepth will generate PGM.  This less intelligent pro-
       gram quite probably is also not intelligent enough to deal with general
       maxvals, so you should specify a depth of 255.

OPTIONS
       The default quantization method is boustrophedonic Floyd-Steinberg  er-
       ror  diffusion (-floyd or -fs).  Also available are simple thresholding
       (-threshold); Bayer's ordered dither (-dither8) with  a  16x16  matrix;
       and three different sizes of 45-degree clustered-dot dither (-cluster3,
       -cluster4, -cluster8).  A space filling curve halftoning  method  using
       the Hilbert curve is also available.  (-hilbert);

       Floyd-Steinberg  will almost always give the best looking results; how-
       ever, looking good is not always what you want.  For instance,  thresh-
       olding  can  be  used  in a pipeline with the pnmconvol tool, for tasks
       like edge and peak detection.   And  clustered-dot  dithering  gives  a
       newspaper-ish look, a useful special effect.

       The  -value  flag alters the thresholding value for Floyd-Steinberg and
       simple thresholding.  It should be a  real  number  between  0  and  1.
       Above 0.5 means darker images; below 0.5 means lighter.

       The Hilbert curve method is useful for processing images before display
       on devices that do not render individual pixels distinctly (like  laser
       printers).  This  dithering  method  can  give  better results than the
       dithering usually done by the laser printers  themselves.   The  -clump
       flag alters the number of pixels in a clump. This is usually an integer
       between 2 and 100 (default 5). Smaller clump sizes smear the image less
       and are less grainy, but seem to loose some grey scale linearity. Typi-
       cally a PGM image will have to be scaled to fit on a laser printer page
       (2400 x 3000 pixels for an A4 300 dpi page), and then dithered to a PBM
       image before being converted to a postscript file.  A printing pipeline
       might  look something like: pnmscale -xysize 2400 3000 image.pgm | pgm-
       topbm -hil | pnmtops -scale 0.25 > image.ps

       All flags can be abbreviated to their shortest unique prefix.

REFERENCES
       The only reference you need for this stuff is "Digital  Halftoning"  by
       Robert Ulichney, MIT Press, ISBN 0-262-21009-6.

       The  Hilbert curve space filling method is taken from "Digital Halfton-
       ing with Space Filling Curves" by Luiz Velho, Computer Graphics  Volume
       25, Number 4, proceedings of SIGRAPH '91, page 81. ISBN 0-89791-436-8

SEE ALSO
       pbmreduce(1), pgm(5), pbm(5), pnmconvol(1), pnmscale(1), pnmtops(1)

AUTHOR
       Copyright (C) 1989 by Jef Poskanzer.

                                 26 July 1988                      pgmtopbm(1)