g3topbm



G3topbm User Manual(0)                                  G3topbm User Manual(0)




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 dou-
       ble 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(1).

       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; some-
              times 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
              option.


       -stretch
              Tells g3topbm to stretch the  image  vertically  by  duplicating
              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  prematurely,  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).  Before 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  Recommendation  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 encoding
       scheme used is differential only over small segments never exceeding  2
       lines  at  standard resolution or 4 lines for fine-detail.  (The incre-
       mental G3 encoding scheme is called two-dimensional and the  number  of
       lines so encoded is specified by a parameter called k.)




SEE ALSO

       pbmtog3(1), pbm(1)



AUTHOR

       Copyright (C) 1989 by Paul Haeberli <paul@manray.sgi.com>.



netpbm documentation            02 October 1989         G3topbm User Manual(0)

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