关键词: 图像压缩, 分形, 分形图像编码, 主对角和特征

Abstract: Fractal image coding has received much interest over the past decade in the area of image processing，especially in the context of image compression.It is hardly useful in reality due to the fatal drawback of being quite time consuming during its encoding process.In order to shorten coding time，the fast scheme is proposed to limit the search space on the basis of an inequality linking the root-mean-square and newly-defined main diagonal sum features of normalized block.It can effectively confine the searching scope of best-matched block for an input range block to the neighbourhood of the initial-matched block（i.e.，the domain block having the closest main diagonal sum features to the input range block being encoded）.Moreover，the scheme further propose two strategies：One is all codebook blocks with small standard deviations can be excluded from the domain pool；the other is range blocks with small standard deviations are directly approximated by the intensity mean block.The algorithm is proved feasible in theroy，simulation test results demonstrate that，for three standard test images，the proposed scheme averagely obtain the speedup of 30 times or so，while can accomplish good quality of the reconstructed images against the full search method.

Key words: image compression, fractal, fractal image coding, main diagonal sum feature