提高分形图像编码质量与速度的方案

分形图像编码十余年来在图像处理尤其是图像压缩领域引起了人们的极大兴趣。众所周知，编码时间长是这项技术的主要缺点，许多改进方案因此被提出以加快编码过程。然而，在这些加快方案中，大多数仅仅是在解码图像质量或多或少有所下降的条件下减少编码时间的。该文提出进一步提高解码图像质量和编码速度的方案：一是预先在待编码图像中添加高斯白噪声以进一步减少不满足对比度因子约束的domain块的数目；二是对小方差range块直接用其均值块代替以进一步加快编码速度。实验结果显示，对于三幅复杂性不同的标准测试图像，本方案确实能够从解码质量和编码速度方面改进传统分形图像编码。

Improving Fractal Image Coding in Terms of Quality and Speed

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 well known that long encoding time is the main drawback of this technique and many improved schemes have been proposed to accelerate the encoding process.However,most of them can reduce the encoding time only at the cost of more or less degradation in the decoded image quality.On the basis of the authors' results published in this journal(No.8,2004),this paper further proposed two strategies which improved both quality and speed of fractal encoding:first,a priori adding additive white Gaussian noise(AWGN) into the image being encoded to reduce the domain blocks that are unlikely to meet the constraint on contrast scaling factors;second,range blocks with small standard deviations are directly approximated by the constant block(i.e.,all the intensity values are replaced by the intensity mean) to accelerate the encoding process.The simulation results demonstrate that,for three standard test images with different complexities,the proposed scheme can really improve the traditional fractal coding method in terms of quality and speed.