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 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 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, pbm  

AUTHOR

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


 

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