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
   output.

   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
   program  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
   error   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;
   however,  looking  good  is  not  always  what you want.  For instance,
   thresholding 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.
   Typically  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 | pgmtopbm -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
   Halftoning  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)

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Free and Open Source Software