1G3topbm User Manual(0) G3topbm User Manual(0)
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6 g3topbm - convert a Group 3 fax file into a PBM image
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10 g3topbm [-kludge] [-reversebits] [-stretch] [-width=pixels |
11 paper_size={A3|A4|A5|A6|B4}] [-stop_error] [g3file]
12 Minimum unique abbreviation of option is acceptable. You may use dou‐
14 ble hyphens instead of single hyphen to denote options. You may use
15 white space in place of the equals sign to separate an option name from
16 its value.
17
20 This program is part of Netpbm(1).
21 g3topbm reads a Group 3 fax file as input and produces a PBM image as
23 output.
24 g3topbm tolerates various deviations from the standard, so as to
26 recover some of the image if there was a transmission error. One thing
27 it tolerates is lines of varying length. The standard requires all the
28 lines to be the same length; g3topbm makes the output image as wide as
29 the longest line in the input and pads the others on the right. It
30 warns you when it does this.
31 You can use the stop_error option to make g3topbm insist on valid
33 input.
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37 -kludge
38 Tells g3topbm to ignore the first few lines of the file; some‐
39 times fax files have some junk at the beginning.
40 -reversebits
43 Tells g3topbm to interpret bits least-significant first, instead
44 of the default most-significant first. Apparently some fax
45 modems do it one way and others do it the other way. If you get
46 a whole bunch of 'bad code word' messages, try using this
47 option.
48 -stretch
51 This option tells g3topbm to stretch the image vertically by
52 duplicating each row. This is for the low-quality transmission
53 mode.
54 -width=pixels
57 This option tells g3topbm that the image is supposed to be pix‐
58 els pixels wide. If any line in it is not that size, g3topbm
59 issues a warning or fails, depending on whether you specify
60 -stop_error.
61 You cannot specify both -width and -paper_size.
63 This option was new in Netpbm 10.33 (March 2006).
65 -paper_size={A3,A4,A5,A6,B4}
68 This option tells g3topbm for what size paper this image is sup‐
69 posed to be formatted. g3topbm uses the width of the paper the
70 same way as with the -width option. g3topbm does not use the
71 height of the paper for anything.
72 You cannot specify both -width and -paper_size.
74 This option was new in Netpbm 10.33 (March 2006).
76 -stop_error
79 This option tells g3topbm to fail when it finds a problem in the
80 input. 'Fail' means it terminates with a nonzero status code
81 with the contents of the output file undefined.
82 If you don't specify this option, g3topbm does its best to work
84 around input errors and salvage as much of the image as possible
85 in the output image. It first tries to resynchronize to a later
86 line by searching for the next End Of Line marker, skipping any
87 lines or partial lines in between. It saves the beginning of
88 the line in which it encountered the problem. If the input file
89 ends prematurely, g3topbm produces output containing the lines
90 up to where it encountered the problem.
91 g3topbm issues warning messages when it continues in spite of
93 input errors.
94 This option was new in Netpbm 10.24 (August 2004). Before that,
96 g3topbm always failed when it encountered premature EOF and
97 never failed when it encountered other problems.
98 <H2 id="g3">ABOUT G3</H2>
102 G3 is the near universal format used by fax machines. There is also a
104 newer, more capable G4.
105 The standard for Group 3 fax is defined in CCITT Recommendation T.4.
107 In the U.S., that is implemented by EIA standards EIA-465 and EIA-466.
108 These standards cover the layers below the image format (which are
109 irrelevant to g3topbm as well.
110 G3 faxes are 204 dots per inch (dpi) horizontally and 98 dpi (196 dpi
112 optionally, in fine-detail mode) vertically. Since G3 neither assumes
113 error free transmission nor retransmits when errors occur, the encoding
114 scheme used is differential only over small segments never exceeding 2
115 lines at standard resolution or 4 lines for fine-detail. (The incre‐
116 mental G3 encoding scheme is called two-dimensional and the number of
117 lines so encoded is specified by a parameter called k.)
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122 pbmtog3(1), pbm(1)
123netpbm documentation 28 February 2006 G3topbm User Manual(0)