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



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(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;  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
              duplicating each row.  This is for the  low-qual-
              ity 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 out-
              put 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 Recom-
       mendation 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)  verti-
       cally.  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  incremental  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@man-
       ray.sgi.com>.



netpbm documentation    02 October 1989  G3topbm User Manual(0)
