CCITT Group 3
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
Specifications
- ITU-T Recommendation T.4
- TIFF 6.0 Specification, Section 10: Modified Huffman Compression
