RAPID CODEBOOK SEARCH ALGORITHM FOR SAR RAW DATA COMPRESSION

This paper presents a simple but eifective algorithm to speed up the codebook search in a vector quantization scheme of SAR raw data when a minimum square error(MSE) criterion is used. A considerable reduction in the number of operations is achieved.     

Embedding of any type of data in images based on a human visual model and multiple-based number conversion

A novel approach to embedding any type of digital data into a cover image is proposed, which utilizes a human visual model to guarantee that the modification of the cover image is imperceptible. A quantized contrast function based on the model is constructed first. The gray values of each 3×3 sub-image of the cover image are used to compute, using the function, a range of gray levels with the same contrast as that of the central pixel of the sub-image. The embedding process proceeds by replacing the gray value of the central pixel by one of the values in the range. This guarantees that the changes be imperceptible. The data to be embedded is treated as a binary stream and is partitioned into a number of sub-streams. A multiple-base number conversion mechanism is used to convert each sub-stream of data into values which are then embedded in the central pixels of sub-images. The embedded data can be extracted out from the resulting stego-image without referencing the original image. Experimental results show that the proposed method is feasible.     

Quantizer design for interconnected feedback control systems

In this paper, we consider the design of interconnected H-infinity feedback control systems with quantized signals. We assume that a decentralized static output feedback has been designed for an interconnected continuous-time LTI system so that the closed-loop system is stable and a desired H-infinity disturbance attenuation level is achieved, and that the subsystems’ measurement outputs are quantized before they are passed to the local controller. We propose a localoutput- dependent strategy for updating the quantizers’ parameters, so that the overall closed-loop system is asymptotically stable and achieves the same H-infinity disturbance attenuation level. Both the pre-designed controllers and the quantizers’ parameters are constructed in a decentralized manner, depending on local information.     

基于最佳位分配技术的图象编码

提出了一个新的位分配算法，它可以有效地分配一个给定的位的限额给任意不同的量化器集合.这种算法产生一个最佳或接近最佳位分配，它允许位分配集合值被限制成非负整数.该算法用在小波图象编码中，实验表明,这种算法是十分有效的.     

框架扩展下的多描述MDSQ编码的改进

数据在差错信道下可能会发生数据包丢失等问题,而研究开发实时并且具有较好鲁棒性的媒体流数据编码已成为当前一个热门研究领域,多描述编码则是解决上述问题的一种很好的编码方式。框架是一组冗余的基,通过框架表示的数据具有很强的差错恢复性和鲁棒性。通过框架扩展对多描述MDSQ算法进行改进。通过实验表明,该算法简单、有效,能够很好地提高数据恢复质量。     

Quantizer offset selection for improved requantization transcoding

In this paper, we provide an analysis of the requantization problem in order to improve the requantization process. This analysis is based on theoretical R-D results of requantized Laplacian sources instead of minimizing requantization errors as commonly found in the literature. We derive the effective quantizer characteristic by applying superposition to the quantizer characteristics of encoder and transcoder. Further investigation shows that the effective quantizer has a periodic property. Using the memoryless property of the probability distribution function and the periodic property of the effective quantizer characteristic, we derive expressions for entropy and distortion. Based on the theoretical R-D model, requantization for fine and coarse quantized signals is investigated. The analysis of the R-D behavior shows that a heuristic can be derived which improves the requantization process. Finally, the results from the R-D analysis are verified for requantization transcoding of H.264/AVC video streams. We show that the transcoding process for H.264/AVC video streams, which corresponds to coarse quantization, is improved with gains up to 1 dB.     

基于量化器优化的JPEG信息隐藏算法

在以保密通信为应用背景的信息隐藏算法中,如何在JPEG文件隐藏大量的信息是一个较有挑战性的问题.本文对在JPEG文件中的高频区隐藏信息的算法进行了介绍分析.并针对该算法在隐藏信息量较大时,载体图像的视觉质量下降较大的缺点,提出了一种基于量化器优化设计的信息隐藏算法.该算法通过量化器的优化设计来抑制嵌入信息时引入的高频噪声,从而达到改善载体图像视觉质量的目的.实验结果证明,这种方法能大量的减少高频噪声的引入.     

Bit plane modification for improving MSE-near optimal DPCM-based block truncation coding

A hybrid method of block truncation coding (BTC) and differential pulse code modulation (DPCM) offers better visual quality than the standard BTC for small block sizes due to its inherent multitone representation. Recently, a two-level quantizer design method has been proposed to increase the coding performance of the DPCM-BTC framework. However, the design method is near optimal in the sense that its coding performance depends on the initial bit plane patterns. In this paper, we propose a bit plane modification (BPM) algorithm to achieve further performance improvement. The BPM algorithm, inspired by error diffusion, effectively distributes large quantization error at a certain pixel to its neighboring pixels having small quantization errors by changing partial bit patterns. Experimental results show that the proposed algorithm successfully achieves much higher coding performance than various conventional BTC methods. The average PSNR performance of the proposed method is 2.31 dB, 5.15 dB, and 5.15 dB higher than that of BTC, DPCM-BTC, and a recently developed BTC scheme using error diffusion and bilateral filtering, respectively.     

一种新的量化反馈控制系统稳定性分析方法

针对一类量化反馈控制系统,在考虑量化范围和量化误差的情况下,建立该系统的动态数学模型.利用Lyapunov稳定性理论,结合线性矩阵不等式(LMI),给出了基于LMI和时变Lyapunov函数的渐近稳定性判据.假设量化器参数满足一定条件,则通过该判据能分析和判定量化反馈控制系统的渐近稳定性,并进一步设计相应的量化反馈控制律.与已有的方法相比,该方法更加有效且求解方便.数值仿真结果表明了该方法的有效性.     

基于最佳量化的序列图像编码转换码率控制策略

该文分析了编码转换缓冲区的状态，导出了编码转换缓冲区为防止解码器缓冲区下道和上道应满足的条件，建立了序列图像编码转换模型．并根据编码转换缓冲器的状态和信道速率，为待编码帧在图像层上预分配目的序列图像编码比特数，使用DCT系数分布特性来表征图像特性．继而为帧内每一具体宏块选定最佳量化因子，提出了基于最佳量化的码率控制策略．模拟实验表明，该码率控制策略能有效地减少、避免缓冲区出现上、下道的情况，使输出码率趋于稳定，提高了重建序列图像的信噪比．