<title>Hybrid fractal image coding method</title>

Abstract

In recent years, fractal image compression has been paid great attention because of its potential of high compression ratio. In the previously published encoding techniques, an image is usually partitioned into nonoverlapping blocks, and each block is encoded by a self-affirm mapping from a larger block. A high cost of the searching process is generally needed to encode a block. With the help of experiments, we discovered blocks do exist which cannot be well matched with any larger blocks under self-affirm transform. To encode these kinds of blocks with the present fractal encoding method may result in relatively low fidelity on these blocks. In this paper, we propose a hybrid fractal encoding method based on DCT and self- affirm transforms to improve local fidelity and encoding speed. The concept of short distance piecewise self-similarity (SDPS) is defined. Those blocks possessing SDPS are encoded with near-center self-affirm transform method. Other blocks are encoded with quasi-JPEG algorithm. Our method makes use of both the advantages of fractal coding technique, possessing the potential of high compression ratio, and the advantages of JPEG algorithm providing high fidelity at low or medium compression.