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 output.

       Note that there is no pbmtopgm converter.  Any program that uses the Netpbm libraries to read PGM files,  including  virtu‐
       ally 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  in‐
       telligent 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  be‐
       tween 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  lin‐
       earity.  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  some‐
       thing 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)