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.

相关反馈方法是对基于内容图像检索系统的有效改进，它将人类视觉特性逐步引入检索过程，有效地减小了图像低层特征表示与图像语义理解之问的差异。但传统的相关反馈算法存在反馈次数多，且无法积累用户反馈信息等缺点。本文针对这些缺点，在相关反馈图像检索系统中引入了可更新特征库。即在原始特征索引库的基础之上引入了一个用户可修改的特征索引库，系统可以将用户多次反馈的信息逐步嵌入到这个特征索引库中。与此同时，我们提出了一种基于多分辨率分析的彩色图像纹理特征描述方法，并将其用于特征库的构建中。我们在一个含有10 000幅图像的图像库上所做的测试结果表明：与Illinois大学的MARS系统相比[1]，本系统可明显提高系统检索准确率和相关反馈的收敛速度。

数字水印技术是现代版权保护的手段之一，而数字水印系统的鲁棒性是其能够起到版权保护作用的必要条件，也是当前的研究热点。本文提出了一种Turbo 编码的图像水印的软判决检测算法，在不改变原有的嵌入算法的前提下，只需在接收端采用软判决检测算法就能有效地提高水印系统的鲁棒性。在本文提出的方案中，首先把原始水印信息进行Turbo 编码，在图像DFT变换域中，修改两个相同频点系数的大小关系来嵌入经过编码的水印信息。在检测水印时，采取软判决检测算法提取用于Turbo 译码的软输入信息，可有效地提高系统的鲁棒性。实验结果表明，软判决检测的比特错误率普遍低于硬判决检测的比特错误率，在高斯噪声情况下，甚至能低0.169。

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 robustness against geometrical attacks remains one of the most challenging issues in watermarking of images and video. This Paper presents several improvements of the video watermarking approach presented in [1], namely (i) using a temporally low-pass watermark and (ii) synchronization to resist attacks along the temporal axis. In order to improve the watermark detection performance. we propose: to rose to use an amplitude. limiting filter and a whitening filter during the watermark extraction process. Experimental results show that the proposed techniques achieve good performanee.