提升小波变换与分形相结合的图像压缩

提出了一种提升小波变换与分形相结合的图像压缩方案.充分利用小波变换后系数能量的分布特性,对提升小波变换后的低频部分采用改进的分形图像压缩编码,其余部分采用集合分裂嵌入块(SPECK)编码算法.试验结果表明,该方法在提高了压缩效率的同时,获得了较高的恢复图像质量.     

基于改进SPECK的雷达图像无损压缩算法

针对VDR雷达图像的无损压缩技术要求高速、高效、低内存占用量的特点,在分析图像整数小波变换的基础上,研究一种基于整数小波和改进SPECK快速无损压缩算法.该算法利用整数小波对图像进行变换,进而采用SPECK进行编码.SPECK算法采用易于计算和并行处理的块结构,不仅提高了编码速度,还具有动态存储小、容错性好等特点.算法中还引入了哈希表和综合匹配法对SPECK算法进行了改进.通过对VDR雷达图像的无损压缩实验证明,该算法不仅提高了压缩速度,而且提高了压缩比,具有广泛的应用价值.     

R-D optimized tree-structured compression algorithms with discrete directional wavelet transform

A new image coding method based on discrete directional wavelet transform (S-WT) and quad-tree decomposition is proposed here. The S-WT is a kind of transform proposed in [V. Velisavljevic, B. Beferull-Lozano, M. Vetterli, P.L. Dragotti, Directionlets: anisotropic multidirectional representation with separable filtering, IEEE Trans. Image Process. 15(7) (2006)], which is based on lattice theory, and with the difference with the standard wavelet transform is that the former allows more transform directions. Because the directional property in a small region is more regular than in a big block generally, in order to sufficiently make use of the multidirectionality and directional vanishing moment (DVM) of S-WT, the input image is divided into many small regions by means of the popular quad-tree segmentation, and the splitting criterion is on the rate-distortion sense. After the optimal quad-tree is obtained, by means of the embedded property of SPECK, a resource bit allocation algorithm is fast implemented utilizing the model proposed in [M. Rajpoot, Model based optimal bit allocation, in: IEEE Data Compression Conference, 2004, Proceedings, DCC 2004.19]. Experiment results indicate that our algorithms perform better compared to some state-of-the-art image coders.