One of the main drawbacks of fractal im-age coding (FIC) is its time-consuming encoding process. So how to speed up the encoding process is a challenging issue of FIC research. As both sequential solutions and parallel ones have their advantages and disadvantages, we combine them together to further speed up the encoding phase. In this paper a derivative tree topology is first pro-posed to provide support for complex parallelism. Then a dual-classification technique is designed for speeding up the fractal image coding with Same-Sized Block Mapping, which improves the decoded image quality. Finally, some experimental results with good performance are presented.

The fractal image coding technique has attracted a degree of interest for its low bit rate. But the reconstructed image is of medium quality. This problem has prevented the fractal technique from being practically used. In order to improve the compression fidelity, a new affine ransformation is roposed in this paper. Meanwhile, its contractivity requirement is analyzed, and the optimal parameters are derived using the least square method. The new affine transformation has been practically used in image coding. Experiments show that the PSNR can reach 28.7dB at a compression ratio (CR) of 16.4 for the 256 256 8 "Lena" image. Comparison with other fractal coding schemes shows that the new affine transformation can improve the reconstructed image quality efficiently.

A new image data compression method using fractals and the discrete cosine transforms (DCT) is presented. The original image is first encoded by fractals in the DCT domain, then the error image is encoded using the DCT. Experiments show that the method can achieve high fidelity at a high compression ratio.

In Fractal image coding (FIC), a parti-tioning of the original im age into ranges and domains is required, which greatly afects the coding performance. Usually, the more adaptive to the image content the partition is, the higher performance it can achieve. Nowadays, some alleged Region-based fractal coders (RBFC) using split-and-merge strategy can achieve better adaptivity and perform ance com pared with traditional rectangular block partitions. However, the regions are still with linear con. tour. In this paper, we present a Freely-shaped Region-based fractal coder rFs. (RBFC) using a two-step partitioning, i. e. coarse partitioning bas ed on fractal dim ension and fine partitioning based on region growth, which brings freely-shaped regions. Our highly im age-adaptive scheme can achieve better rate. distortion curve than conventional scheme, even more visually pleasing resultsat the same perform ance.

目前，大多数鲁棒图像水印所面临的最大问题就是几何攻击，而几何攻击又以仿射变换为主，攻击者只需对目标图像做轻微的几何形变就可以使嵌入其中的水印信息失效。本文在PingDong等人提出的基于图像归一化方法的抵抗任意仿射变换攻击的鲁棒数字水印的基础上[1]，改进了原有的归一化方法，去掉了归一化过程中的约束条件，简化了归化的过程。并且在此基础上提出一种新的水印嵌入方案，克服了文献[1]中水印方案水印不可见性较差的问题。实验证明，本文提出的方案对仿射变换攻击具有很好的鲁棒性，嵌入的水印容量较大且水印图像的质量较高。