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 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 gen-
       eral 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 (-clus-
       ter3, -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, 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. 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)