An Extension of the CCITT Facsimile Codes for Dithered Pictures
O. Johnsen, Arun N. Netravali · Bell System Technical Journal · 1981
The International Telegraph and Telephone Consultative Committee (CCITT) has recently recommended two redundancy reduction codes for the digital transmission of two-level facsimile. It is of interest to transmit other types of still pictures using these codes. In this paper we develop a method for bilevel dithered pictures, wherein pictures are preprocessed reversibly to permit efficient coding by the CCITT codes. The preprocessing consists of local rearrangement of picture elements to obtain large contiguous black and white areas. The main advantage of these schemes over the existing ones is that they require the addition of a simple processor to a standardized facsimile coder. One of the schemes has the additional advantage that even in the absence of the postprocessor at the receiver, a distorted but recognizable picture is obtained. A compression ratio of 1.5 to 3.5 is obtained with these methods, which is comparable with other coding schemes.