3.6 Additional tools for working with g3 files

Some additional tools are provided for manipulating G3 fax files:

• g3cat (in the g3/ directory) concatenates multiple G3 fax files. It accepts “raw” g3 files and digifax files and outputs a “raw” g3 file without headers. Its syntax is analogous to cat, except that you have to specify - to read from stdin.

  g3cat recognizes two flags: -l, to separate the fax files with a thin black line, and -a to byte-align the end-of-line codes in the file (Warning: some modems do not like this).

• To convert an incoming fax to Jef Poskanzers portable bitmap (pbm) format, you can use the g32pbm program that is also provided in g3/. It’s advantages over Jef’s g3topbm program are that it’s approximately five times faster and takes only one eigth as much virtual memory (on machines with low virtual memory, it can thus be up to 100 times faster!). Its disadvantage is that it produces only “raw” (i.e., binary) pbm files; and it’s not as stable when handling erroneous g3 data (means that if one line is severly corrupted, it can happen that the next line will not be decoded properly. The rest of the file will then be OK again).

  Syntax:

  g32pbm [-r] [-s] [-l] [-d <dpi>] [g3-file]
  

  If no g3 file is specified, standard input is used.

  The -s(tretch) option causes g32pbm to double each row of the g3 file. You can use this to adjust the aspect ratio of a "normal" resolution fax file to match that of a "fine" resolution fax. Of course you can use other pbmplus tools for this instead, but -s is sure to be faster.

  If you have a HP Laserjet printer, you can make g32pbm output HP LJ data with the -l switch. The desired resolution is chosen with the -d 75|150|300 switch.

• For the other direction, I have provided a pbm2g3 program that will convert Jef Poskanzer’s Portable BitMap format into G3 fax data suitable for faxing with sendfax. The pbm files can be produced by various sources, e.g. drawing programs (xpaint), bitmap manipulation programs (xv), or simply be converted from other file formats by means of the pbmplus tools.

  As above, my variant is a lot faster than Jef’s, and unlike his, it produces g3 data that adheres to the T.4 standard (if you don’t fiddle too much with the options...), so you don’t have to apply any patches to make it work together with sendfax.

  Syntax:

  pbm2g3 [-r] [-a] [-w page with] [-h blank lines] [pbm-file]
  

  if no pbm file is specified, standard input is used.

  For a detailed description, see the pbm2g3(1) man page.

• viewfax. To view G3 data files under X11, Frank D. Cringle has written a very nice and fast tool that will display the files on screen, turn them, zoom them in and out, …

  The source code can be found in the mgetty/frontends/X11 directory. It’s not (yet) built and installed by default, but it’s straightforward.

  For a detailed description, see the README and viewfax.man files in that directory.

• To convert an incoming fax into X-Windows xwd bitmaps, you can use Chel van Gennip’s g3toxwd program, found in the contrib/ directory.
• If you want to print out faxes on a HP laserjet printer, you have two opions: you can use Chel’s g3tolj program (also in the contrib/ directory), or you use my g32pbm program with the -l option, which will make it output LJ data.