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AN IMPROVED PHASE SPAN SEARCH STRATEGY FOR FRACTAL IMAGE CODING

In this paper, an improved phase span search strategy is proposed to speedup the fractal encoder. First, a coordinate system is constructed using the two lowest discrete cosine transformation (DCT) coefficients of image blocks. By mapping image blocks into the coordinate system, some image blocks with similar edge shapes will be concentrated on a specific region. Therefore the purpose of speedup can be reached by limiting the search space on the specific region. Second, embedding the edge property into the search strategy, the speedup ratio will can be lifted further. Experimental results show that, compared with the full search method, the encoding speed of the proposed method is about 94 times faster, while the penalty of retrieved image quality is only decaying 0.9 dB.