Nathanael J. Brittain and Mahmoud R. El-Sakka, "Grayscale Two-Dimensional Lempel-Ziv Encoding", International Conference on Image Analysis and Recognition, ICIAR'2005, LNCS 3656, pp. 328-334, Springer-Verlag Berlin Heidelberg, September 2005, Toronto, Canada.
Dictionary-based compression methods are a popular form of data file compression. LZ77, LZ78 and their variants are likely the most famous of these methods. These methods are implemented to reduce the one-dimensional correlation in data, since they are designed to compress text. Therefore, they do not take advantage of the fact that, in images, adjacent pixels are correlated in two dimensions. Previous attempts have been made to linearize images in order to make them suitable for dictionary-based compression, but results show that no single linearization is best for all images. In this paper, a true two-dimensional dictionary-based lossless image compression scheme for grayscale images is introduced. Testing results show that the compression performance of the proposed scheme outperforms and surpasses any other existing dictionary-based compression scheme. The results also show that it slightly outperforms JPEG-2000's compression performance, when it operates in its lossless mode, and it is comparable to JPEG-LS's compression performance, where JPEG-2000 and JPEG-LS are the current image compression standards.