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G3topbm User Manual(0) G3topbm User Manual(0)
NAME
g3topbm - convert a Group 3 fax file into a PBM image
g3topbm [-kludge] [-reversebits] [-stretch] [{-width=pixels |
paper_size={A3,A4,A5,A6,B4}] [-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.
This program is part of Netpbm(1).
g3topbm reads a Group 3 fax file as input and produces a PBM image as
output.
g3topbm tolerates various deviations from the standard, so as to
recover some of the image if there was a transmission error. One thing
it tolerates is lines of varying length. The standard requires all the
lines to be the same length; g3topbm makes the output image as wide as
the longest line in the input and pads the others on the right. It
warns you when it does this.
You can use the stop_error option to make g3topbm insist on valid
input.
-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
This option tells g3topbm to stretch the image vertically by
duplicating each row. This is for the low-quality transmission
mode.
-width=pixels
This option tells g3topbm that the image is supposed to be pix-
els pixels wide. If any line in it is not that size, g3topbm
issues a warning or fails, depending on whether you specify
-stop_error.
You cannot specify both -width and -paper_size.
This option was new in Netpbm 10.33 (March 2006).
-paper_size={A3,A4,A5,A6,B4}
This option tells g3topbm for what size paper this image is sup-
posed to be formatted. g3topbm uses the width of the paper the
same way as with the -width option. g3topbm does not use the
height of the paper for anything.
You cannot specify both -width and -paper_size.
This option was new in Netpbm 10.33 (March 2006).
-stop_error
This option 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.
<H2 id="g3">ABOUT G3</H2>
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.)
pbmtog3(1), pbm(1)
netpbm documentation 28 February 2006 G3topbm User Manual(0)
Man(1) output converted with
man2html and wrapped by fishsponge
This page was generated on Sat Sep 8 16:34:45 GMT 2007
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