g3topbm

   Updated: 02 October 1989
   Table Of Contents

NAME

   g3topbm - convert a Group 3 fax file into a PBM image

SYNOPSIS

   g3topbm   [-kludge]	[-reversebits]	[-stretch]  [-stop_error]
[g3file]

   Minimum unique abbreviation of option is acceptable.	 You  may
use double
   hyphens  instead  of	 single hyphen to denote options. You may
use white space
   in place of the equals sign to separate an  option  name  from
its value.

DESCRIPTION

   This program is part of Netpbm.

   g3topbm   reads a Group 3 fax file as input and produces a PBM
image as
   output.

OPTIONS

   -kludge
	  Tells g3topbm to ignore the  first  few  lines  of  the
file; sometimes
	  fax files have some junk at the beginning.
   -reversebits
	  Tells	  g3topbm  to  interpret  bits	least-significant
first, instead of
	  the default most-significant first. Apparently some fax
modems do it
	  one  way  and	 others do it the other way. If you get a
whole bunch of
	  "bad code word" messages, try using this flag.
   -stretch
	  Tells g3topbm to stretch the image vertically by dupli-
cating each
	  row. This is for the low-quality transmission mode.
   -stop_error
	  Tells	 g3topbm  to  fail when it finds a problem in the
input. "Fail"
	  means it terminates with a nonzero status code with the
contents of
	  the output file undefined.
	  If you don't specify this option, g3topbm does its best
to work
	  around input errors and salvage as much of the image as
possible in
	  the  output image. It first tries to resynchronize to a
later line by
	  searching for the next End Of Line marker, skipping any
lines or
	  partial lines in between. It saves the beginning of the
line in which
	  it encountered the problem. If the input file ends pre-
maturely,
	  g3topbm   produces  output  containing  the lines up to
where it
	  encountered the problem.
	  g3topbm issues warning messages when	it  continues  in
spite of input
	  errors.
	  This	option was new in Netpbm 10.24 (August 2004). Be-
fore that,
	  g3topbm always failed when it encountered premature EOF
and never
	  failed when it encountered other problems.



ABOUT G3

   G3 is the near universal format used by fax machines. There is
also a newer,
   more capable G4.

   The standard for Group 3 fax is defined in  CCITT  Recommenda-
tion T.4. In the
   U.S.,   that	 is  implemented  by  EIA  standards  EIA-465 and
EIA-466. These
   standards cover the layers below the image format  (which  are
irrelevant to
   g3topbm as well.

   G3	faxes are 204 dots per inch (dpi) horizontally and 98 dpi
(196 dpi
   optionally, in fine-detail mode) vertically. Since G3  neither
assumes error
   free	 transmission  nor retransmits when errors occur, the en-
coding scheme
   used is differential only over small segments never	exceeding
2 lines at
   standard resolution or 4 lines for fine-detail. (The incremen-
tal G3 encoding
   scheme is called two-dimensional and the number  of	lines  so
encoded is
   specified by a parameter called k.)

SEE ALSO

   pbmtog3, pbm

AUTHOR

   Copyright (C) 1989 by Paul Haeberli .
     _________________________________________________________________



Table Of Contents

     * NAME
     * SYNOPSIS
     * DESCRIPTION
     * OPTIONS
     * ABOUT G3
     * SEE ALSO
     * AUTHOR

UNIX/Linux commands referenced on this page:

1. convert
2. file
3. as
4. at
5. more
6. pbmtog3