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将值域块分为自相似值域块和非自相似值域块两大类，其中非自相似值域块是导致分形图像编码速度低的主要原因之一．定义了值域决的零位移自相似系数和σ－α空间，研究了两类值域块在σ－α空间中的分布规律，据此建立了一种分类模型，可以方便地将这两类值域块区分开来．实验结果表明，在压缩比和恢复图像质量受损不大的情况下，基于这一分类模型的分形图像编码方法的编码速度有了显著提高．
The value range block is divided into two categories: self-similar range block and non-self-similar range block, among which the non-self-similar range block is one of the main reasons leading to the low speed of the fractal image coding. The zero-displacement self-similarity coefficient and σ-α space are defined. The distribution of two types of range block in σ-α space is studied. A classification model is established, Value range block to distinguish. The experimental results show that the coding speed of the fractal image coding method based on this classification model has been greatly improved under the condition of less compression ratio and less damaged image quality.