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Huffman Encoding

A modified version of run-length encoding is Huffman encoding. It is used for
many software based document imaging systems. It is used for encoding the pixel
run length in CCITT Group 3 1-dGroup 4.

It is variable-length encoding. It generates the shortest code for frequently
occurring run lengths and longer code for less frequently occurring run lengths.

Advantages of CCITT Group 3 ID

CCITT Group 3 compression has been used extensively due to the following two
advantages: It is simple to implement in both hardware and software .

It is a worldwide standard for facsimile which is accepted for document imaging
application. This allows document imaging applications to incorporate fax

documents easily.

 CCITT group 3 compressions utilizes Huffman coding to generate a set of
make-up codes and a set of terminating codes for a give bit stream.
 CCITT Group 3 uses a very simply data format. This consists of sequential
blocks of data for each scanline.

CCITT Group 3 2D Compression
It is also known as modified run length encoding. It is used for software based
imaging system and facsimile. It is easier to decompress in software than CCITT
Group 4.
The CCITT Group 3 2D scheme uses a "k" factor where the image is divided into
several group of k lines. This scheme is based on the statistical nature of images;
the image data across the adjacent scanline is redundant. If black and white
transition occurs on a given scanline, chances are the same transition will occur
within + or - 3 pixels in the next scanline.

Necessity of k factor
When CCITT Group 3 2D compression is used, the algorithm embeds Group 3 1
D coding between every k groups of Group 3 2D coding, allowing the Group 3 1
D coding to be the synchronizing line in the event of a transmission error.

Therefore, when a transmission error occurs due to a bad communication link,
the group 3 I D can be used to synchronize and correct the error.