CCITT Group 3

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{{FormatInfo
 
{{FormatInfo
 
|formattype=electronic
 
|formattype=electronic
|subcat=Graphics
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|subcat=Compression
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|subcat2=Fax formats
 
|extensions={{ext|g3}}
 
|extensions={{ext|g3}}
 +
|mimetypes={{mimetype|image/g3fax}}
 
|pronom={{PRONOM|x-cmp/14}}
 
|pronom={{PRONOM|x-cmp/14}}
 
}}
 
}}
'''CCITT Group 3''' is a lossless compressed data format for bi-level images. It is also known as '''T4''', '''T.4''', '''Fax3''', '''Group 3''', '''G3''', or '''ITU-T Fax Group 3'''. It is one of the formats used by fax machines. It is usually embedded in another image file format such as [[TIFF]], but can be stored in a file by itself.
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'''CCITT Group 3''' is a lossless compressed data format for bi-level images. It is also known as '''T4''', '''T.4''', '''Fax3''', '''Group 3''', '''G3''', or '''ITU-T Fax Group 3'''. It is one of the formats used by [[fax machine]]s. It is usually embedded in another image file format such as [[TIFF]], but can be stored in a file by itself.
  
 
It comes in two main varieties: so-called '''1-dimensional''' and '''2-dimensional''' (though both are used on 2-dimensional images). The 1-dimensional variety uses [[Modified Huffman]] (MH) compression, and the 2-dimensional variety uses [[Modified READ]] (MR) compression.
 
It comes in two main varieties: so-called '''1-dimensional''' and '''2-dimensional''' (though both are used on 2-dimensional images). The 1-dimensional variety uses [[Modified Huffman]] (MH) compression, and the 2-dimensional variety uses [[Modified READ]] (MR) compression.
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== Related formats ==
 
== Related formats ==
  
In a [[TIFF]] file, compression type 2 is a type of 1-dimensional CCITT Group 3. Compression type 3 without T4Options bit 0 set is a slightly different type of 1-dimensional CCITT Group 3. Compression type 3 with T4Options bit 0 set is 2-dimensional CCITT Group 3.
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Many of the formats listed in the [[Fax formats]] article use CCITT Group 3 compression.
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In a [[TIFF]] file, compression codes 2, 3, and 32771 are varieties of CCITT Group 3 compression.
  
 
Other formats that can use CCITT Group 3 compression include [[PDF]] and [[SPIFF]].
 
Other formats that can use CCITT Group 3 compression include [[PDF]] and [[SPIFF]].
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== Specifications ==
 
== Specifications ==
* [http://www.itu.int/rec/T-REC-T.4/en ITU-T Recommendation T.4]
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* [https://www.itu.int/rec/T-REC-T.4/en ITU-T Recommendation T.4]
* [http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf TIFF 6.0 Specification], Section 10: Modified Huffman Compression
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* [https://www.adobe.io/open/standards/TIFF.html Adobe TIFF standards] → TIFF6.pdf, Section 10: Modified Huffman Compression - Defines a slightly simplified form of the 1-d format
  
 
== Software ==
 
== Software ==
* [http://netpbm.sourceforge.net/ Netpbm] (g3topbm, pbmtog3)
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* [[Konvertor]]
* [http://www.imagemagick.org/ ImageMagick] (format named "FAX")
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* [[Netpbm]]: g3topbm, pbmtog3
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* [[ImageMagick]] (format named "FAX")
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* [[Farbfeld Utilities]]
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== Links ==
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* RFC 1494: Equivalences between 1988 X.400 and RFC-822 Message Bodies
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* RFC 2159: A MIME Body Part for FAX
  
[[Category:Compression]]
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[[Category:Graphics]]
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[[Category:Fax]]

Revision as of 14:23, 2 December 2020

File Format
Name CCITT Group 3
Ontology
Extension(s) .g3
MIME Type(s) image/g3fax
PRONOM x-cmp/14

CCITT Group 3 is a lossless compressed data format for bi-level images. It is also known as T4, T.4, Fax3, Group 3, G3, or ITU-T Fax Group 3. It is one of the formats used by fax machines. It is usually embedded in another image file format such as TIFF, but can be stored in a file by itself.

It comes in two main varieties: so-called 1-dimensional and 2-dimensional (though both are used on 2-dimensional images). The 1-dimensional variety uses Modified Huffman (MH) compression, and the 2-dimensional variety uses Modified READ (MR) compression.

Contents

Related formats

Many of the formats listed in the Fax formats article use CCITT Group 3 compression.

In a TIFF file, compression codes 2, 3, and 32771 are varieties of CCITT Group 3 compression.

Other formats that can use CCITT Group 3 compression include PDF and SPIFF.

See also

Specifications

Software

Links

  • RFC 1494: Equivalences between 1988 X.400 and RFC-822 Message Bodies
  • RFC 2159: A MIME Body Part for FAX
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