CCITT Group 3

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'''CCITT Group 3''' is a lossless compression algorithm for bilevel images. It is also known as '''T.4''', '''Fax 3''', and '''ITU-T Fax Group 3'''. It is commonly used for storing scanned images, usually in [[TIFF]] format. It is notable in that it is sometimes used in fax transmission.
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'''CCITT Group 3''' is a lossless compression algorithm for bi-level images. It is also known as '''T4''', '''T.4''', '''Fax3''', '''G3''', or '''ITU-T Fax Group 3'''. It is one of the formats used by fax machines, and can be used in some image file formats, such as [[TIFF]].
  
It comes in two main varieties: so-called '''1-dimensional''' and '''2-dimensional''' (though both are used on 2-dimensional images).
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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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The 1-dimensional variety uses [[Modified Huffman]] compression (= [[Run-length encoding|RLE]] + [[Huffman coding]], sometimes abbreviated "MH").
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The 2-dimensional variety uses [[Modified READ]] compression (= delta + RLE + Huffman coding, sometimes abbreviated "MR").
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== Related formats ==
 
== Related formats ==
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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.
 
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.
  
In theory, CCITT Group 3 can be used in [[SPIFF]] files (compression types 1 and 2).
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Other formats that can use CCITT Group 3 compression include [[PDF]] and [[SPIFF]].
  
 
== See also ==
 
== See also ==

Revision as of 20:29, 28 February 2013

File Format
Name CCITT Group 3
Ontology
PRONOM x-cmp/14

CCITT Group 3 is a lossless compression algorithm for bi-level images. It is also known as T4, T.4, Fax3, G3, or ITU-T Fax Group 3. It is one of the formats used by fax machines, and can be used in some image file formats, such as TIFF.

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.

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.

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

See also

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