3

05

54

Glossary coding

Definition of coding

coding

1.  In fax transmission, coding refers to run-length coding, which is a code set used when encoding (shortening) data sent during transmission. Run-length coding is used in CCITT Group 3 and Group 4 compression methods.

More Information:
When scanning a line of pixels in a fax, a single bit can represent a pixel (1 for black and 0 for white). A scan line could be transmitted as a sequence of these bits, but this is not generally efficient, since there can be long sequences of the same bit value. In run-length coding, rather than send the entire list of bits, the data is recoded as the bit color followed by the number of bits of that color. For example, a scan line containing the bits 00011111100011 could be shortened by run-length coding as (0,3) (1,6) (0,3) (1,2). For even more efficiency, if we transmitted the first "color" bit and quantity (0,3 in the example), we do not need to include any of the following "color" bits (since each will be the opposite of the prior one), and we can shorten it to 0,3,6,3,2. This method greatly improves efficiency during data transmission.

• Related terms: CCITT, group (G3)