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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
commit | fc22b3d6507c6745911b9dfcc68f1e665ae13dbc (patch) | |
tree | ce1e3bce06471410239a6f41282e328770aa404a /upstream/mageia-cauldron/man1/faxformat.1 | |
parent | Initial commit. (diff) | |
download | manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.tar.xz manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.zip |
Adding upstream version 4.22.0.upstream/4.22.0
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'upstream/mageia-cauldron/man1/faxformat.1')
-rw-r--r-- | upstream/mageia-cauldron/man1/faxformat.1 | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/upstream/mageia-cauldron/man1/faxformat.1 b/upstream/mageia-cauldron/man1/faxformat.1 new file mode 100644 index 00000000..3749d8d7 --- /dev/null +++ b/upstream/mageia-cauldron/man1/faxformat.1 @@ -0,0 +1,105 @@ +\ +.\" This man page was generated by the Netpbm tool 'makeman' from HTML source. +.\" Do not hand-hack it! If you have bug fixes or improvements, please find +.\" the corresponding HTML page on the Netpbm website, generate a patch +.\" against that, and send it to the Netpbm maintainer. +.TH "Fax Formats" 1 "03 December 2008" "netpbm documentation" + +.SH SYNOPSIS +.PP +This page, part of the +.BR "Netpbm user's guide" (1)\c +\&, +describes FAX formats in relation to Netpbm facilities. + +.SH DESCRIPTION +.PP +The ITU (formerly CCITT) publishes standards for operation of fax machines +(the idea is to provide a way to be sure that a fax machine is able to receive +a fax sent by another). These standards incidentally specify graphics file +formats -- a protocol for representing a visual image in sequences of bits. +.PP +The two relevant standards are called Group 3 (G3) and Group 4 (G4) (Groups +1 and 2 are analog standards no longer in use). Virtually every fax machine +in existence conforms at least generally to at least one of these standards. +.PP +The standard for Group 3 fax is defined in ITU Recommendation T.4. In the +U.S., that is implemented by EIA standards EIA-465 and EIA-466. These +standards cover more than the file format as well, including how to transmit +bits over a telephone line and procedures for handling document transmissions. +.PP +G3 faxes are 204 dots per inch (dpi) horizontally and 98 dpi (196 +dpi optionally, in fine-detail mode) vertically. +.PP +The standards specify three file formats (also called coding methods and +compression schemes -- remember the standard doesn't mention computer files; +it talks about the format of a stream of bits travelling over a telephone +line): + + + +.TP +MH +This compresses in one dimension: it compresses individual raster lines +but makes no attempt to compress redundancy between lines. +.sp +One dimensional compression is traditionally the best a fax machine could +handle because G3 neither assumes error free transmission not retransmits when +errors occur, and receiving fax machines traditionally could not afford to +buffer much of a page. It's important that when there is an error in a raster +line, its impact not spread to many lines after it. +.sp +All Group 3 and Group 4 fax machines must be able to send and receive MH. +.sp +MH is sometimes called "G3," but that is a poor name because +while the Group 3 standard does specify MH, it has always specified other +formats too. +.sp +MH is sometimes called "T4" based on the name of the +document that specifies it, ITU T.4. But this is a poor name because +T.4 also specifies MR. + + +.TP +MR +This compresses in two dimensions, horizontally and vertically. +.sp +MR has always been part of the Group 3 standard, but is optional +(a Group 3 fax machine may or may not be able to send and receive it). + +.TP +MMR +This is a more advanced format than the others. It is even more +two-dimensional than MR. It is optional in the Group 3 standard, and didn't +even exist in earlier versions of it. It was developed specifically for the +Group 4 standard, but then added to an extended Group 3 standard as well. +.sp +MMR is sometimes called Group 4, but that is a poor name because of +the fact that it is also part of the current Group 3 standard. +.sp +MMR is sometimes called "T6" based on the name of the document + that specifies it, ITU T.6. + + +.PP +\fBg3topbm\fP converts the MH format to PBM. \fBpbmtog3\fP converts +PBM to MH. +.PP +There is no Netpbm program to convert to or from other fax formats. + +.SH TIFF +.PP +The TIFF format is flexible enough to allow lots of different coding +methods, within it. There are TIFF subformats for MH, MR, and MMR, among +others. These are particularly useful when you receive a fax as a TIFF file. +.PP +\fBtifftopnm\fP recognizes and can convert from any of these. +.PP +\fBpamtotiff\fP can convert to any of these; you use command options +to choose which. +.SH DOCUMENT SOURCE +This manual page was generated by the Netpbm tool 'makeman' from HTML +source. The master documentation is at +.IP +.B http://netpbm.sourceforge.net/doc/faxformat.html +.PP
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