CCITT stands for Comité Consultatif International Téléphonique et Télégraphique which is an organization that sets international communication standards. The groups below are groups determined by CCITT of which image compression we support.
CCITT Group 3 is the universal protocol for sending fax documents through a phone line. In this group each scan line is encoded independently.
CCITT Group 3 1D - a scan line is encoded as a set of runs, each representing a number of white or black pixels, with white and black runs alrenating. Every run is encoded using a different number of bits, which can be uniquely identified when decoded. Reoccurring lengths of runs will be encoded efficiently, while infrequent runs cause the size to grow.
CCITT Group 3 1D with no EOLs -
CCITT Group 3 2D - G3 2-D is a combination of G3 1-D and G4 compression schemes.
CCITT Group 4 is a protocol used for sending fax documents through an ISDN line. In this group scan lines are encoded with reference to the previous one, creating better compression ratios.
CCITT Group 4 2D - encoding is more than Group 3 encoding. Each scan line is compared to the scan line before it. High levels of compression can be used based on vertical attributes of the image.
| CCITT | JPEG | LZW |
| Pack Bits | RLE | Huffman |