Novel hybrid fractal image encoding algorithm using standard deviation and DCT coefficients

In this paper, a fast fractal encoding algorithm using standard deviation (STD) and DCT coefficients is proposed. First, the STD values of domain blocks are calculated. Then, domain blocks are sorted by their STD values. During the encoding process, each range block is limited to search in the domain blocks with similar STD values. Since the searching space is reduced, the encoding speed is improved. Moreover, for improving the quality of the retrieved image, an auxiliary encoding algorithm (AEA) is proposed, and it could encode range blocks in which the pixel values fluctuate greatly. In the decoding step, a kind of simple line fitting on block boundaries is used to reduce the blocking effects. Simulation results show that the runtime of the proposed method is reduced greatly compared to the full search method. And the new algorithm could obtain good quality and higher compression ratio than the baseline encoding algorithm.