DPCM variable length coding system for image using bifix‐free pattern
Tadao Saito, Hiroshi Inose, Kazuhisa Yanaka · Electronics and Communications in Japan (Part I Communications) · 1981
Abstract In the past, variable length DPCM coding of gray scale image utilized block coding such as Hoffman coding scheme. However, if the midriser quantizer is used, the two levels close to zero level will occur with high probability. In such a case, the Huffman coding without extending the information source still results in a considerable level of redundancy. This is because the codewords can exist only at the tips of the branches of the coding‐tree, which is the constraint for the instantaneously decodable block code. This paper proposes a coding scheme which applies a technique similar to that used for transparency acquisition in the HDLC scheme, to insert a dummy bit into the non‐blocked codewords. In principle, it uses the properties of the bifix‐free pattern. When the two quantized levels close to zero occur with high probability, the proposed coding scheme yields a higher compression factor than does the Huffman code. Furthermore, the coding parameters can be varied adaptively depending on the properties of the image. Both the theoretical aspect of the proposed scheme and the simulation based on the standard test images are discussed in this paper.