八向对称重用策略降低全景图像查表展开法查找表空间

为解决全景图像查表展开法所需查找表空间过大问题,提出八向对称重用的策略.首先,把展开前圆环状全景图像看作一系列同心圆环,沿圆心将这些圆环均匀划分成八个对称的扇形区域.然后,利用空间几何对称性原理,建立八个区域中像素点之间的对称变换关系,这样只需保存一个扇形区域的全景变换像素坐标映射结果,从而将查找表存储空间降低为原来的八分之一.嵌入式应用实验表明,与传统的全景图像查表展开方法相比,所提出方法不仅将所需查找表存储空间降低了8倍,而且将全景图像展开速度平均提高2.74倍.     

面向高光谱分类的局部几何稀疏保持嵌入EI北大核心CSCD

大量维数约简(Dimensionality reducion, DR)方法表明保持数据间稀疏特性的同时,确保几何结构的保持能更有效提取出具有鉴别性的特征,为此本文提出一种联合局部几何近邻结构和局部稀疏流形的维数约简方法.该方法首先通过局部线性嵌入方法重构每个样本以保持数据的局部线性关系,同时计算样本邻域内的局部稀疏流形结构,在此基础上通过图嵌入框架保持数据的局部几何近邻结构和稀疏结构,最后在低维嵌入空间中使类内数据尽可能聚集,提取低维鉴别特征,从而提升地物分类性能.在Indian Pines和PaviaU高光谱数据集上的实验结果表明,本文方法相较于传统维数约简方法能明显提高地物的分类性能,总体分类可达到83.02%和91.20%,有利于实际应用.     

适用于嵌入式系统的二维DCT算法

提出一种简单、快速的二维DCT算法,即将二维DCT的变换系数和图像的像素值事先 乘好,形成查找表,在实现直接二维DCT变换时,把表调入内存,乘积的结果就能通过寻址的方式得 到而无需乘法器,速度很快,非常适合嵌入式系统的设计。在设计查找表时,优化了其结构,减小了存 储空间。实验结果表明了算法的有效性。     

向量运算中的ROM表压缩技术研究

本文对向量内积运算电路实现过程中的ROM表容量需求进行了研究.由于传统实现方法中ROM表的大小随向量维数N呈指数增长,因此ROM表压缩技术十分重要.在分析OBC编码和部分和技术的基础上,本文提出了基于级联技术的压缩方法.理论分析表明先部分和再OBC编码的级联技术具有更好的压缩效果,将该方法在DCT中的实验进一步验证了该结论.     

一种新的广义Hough变换算法

广义Hough变换(GHT)是检测不规则图形的一个有效方法.但是在检测不规则多边形图形时,由于建立参考表R要以梯度为索引项,使得某几个梯度值中的条目数过多,在向参数空间映射时会造成大量的投票冗余,从而影响了变换的效率.而改进的GHT算法在建立参考表时采用了几何特征角来代替梯度,使得建立的R表中各梯度索引项的条目数分布的更均匀,减少了参数空间的投票冗余,提高了算法的效率.实验证明该改进方法的有效性.     

核稀疏保留投影及在步态识别中的应用

针对已有基于线性变换的稀疏保留投影方法在解决实际问题时,会遇到维数灾难和小样本问题.通过引入核方法,提出一种核稀疏保留投影方法.首先采用非线性变换将原始数据映射到高维特征空间,而后在这个高维空间进行稀疏重构,并对得到的系数矩阵进行降维优化,最终得到所需的投影矩阵.将其应用到步态识别中,采用CASIA(B)步态数据库进行实验分析,实验结果表明,本文方法取得了令人满意的识别效果.     

面向打印的光谱色彩管理中间空间构造方法

针对光谱色彩管理中光谱空间维度高引起多光谱图像处理时间长、所需存储空间大的问题,提出构造中间空间的方法。首先通过分析色彩管理过程,引入中间空间,建立以中间空间为设备无关颜色空间的光谱色彩管理流程;然后针对多光谱图像的打印输出,采用主成分分析法对打印机特征化光谱样本进行降维,将降维后的特征空间作为中间空间;最后采用特征向量矩阵实现任意多光谱图像数据到中间空间的变换。实验表明,采用打印机特征化光谱样本生成的中间空间与光谱空间的变换效率高,变换的光谱和色度精度高,图像数据降维后能保持源图像光谱的主要信息。     

自适应加权特征字典与联合稀疏相结合的遥感目标检测

随着分辨率的提高,遥感图像空间包含的有用信息越来越丰富,这使得遥感数据的处理变得更加复杂,容易发生维数灾难并影响识别效果。针对这一情况,提出一种自适应加权特征字典与联合稀疏相结合的遥感图像目标检测方法(GJ-SRC)。首先将训练图像和待测图像进行Gabor变换以提取特征图像。然后计算各个特征值在进行稀疏表示时的贡献权重,通过自适应方法构造特征字典,使字典具有更强的判别能力。最后,提取每一类图像的公共特征和单个图像的私有特征构成联合字典,并利用测试图像稀疏表示进行目标检测识别。为了避免Gabor变换产生的维数灾难,在处理过程中采用PCA方法对特征字典进行降维,以降低计算成本。实验表明,与现有的SRC方法和遥感目标检测方法等相比,所提方法具有较好的检测效果。     

一种有效的高属性维稀疏数据聚类算法

聚类分析是数据挖掘最常见的技术之一,数据的规模、维数和稀疏性都是制约聚类分析的不同方面.本文提出一种有效的高属性维稀疏数据聚类方法.给出稀疏相似度、等价关系的相似度、广义的等价关系的定义.基于对象间的稀疏相似度和等价关系原理形成初始等价类,通过等价关系的相似度修正初始等价关系,使得最终聚类结果更合理.该算法聚类过程不依赖于输入样本的排列顺序,高维稀疏数据的有效压缩提高算法在维数较高时的执行效率,适合于高维稀疏数据的聚类分析.     

基于局部线性逼近的流形学习算法

流形学习方法是根据流形的定义提出的一种非线性数据降维方法,主要思想是发现嵌入在高维数据空间的低维光滑流形.局部线性嵌入算法是应用比较广泛的一种流形学习方法,传统的局部线性嵌入算法的一个主要缺点就是在处理稀疏源数据时会失效,而实际应用中很多情况还要面对处理源数据稀疏的问题.在分析局部线性嵌入算法的基础上提出了基于局部线性逼近思想的流形学习算法,其通过采用直接估计梯度值的方法达到局部线性逼近的目的,从而实现高维非线性数据的维数约简,最后在S-曲线上进行稀疏采样测试取得良好降维效果.     

Comparison of numerical and computational aspects between two constraint-based contact methods in the description of wheel/rail contacts

Multibody System Dynamics - The numerical and computation aspects of the Knife-edge Equivalent Contact (KEC) constraint and lookup table (LUT) methods are compared in this paper. The LUT method...     

用于功放线性化的自适应预失真可变索引方法研究及实现

该文提出了一种用于功放线性化的预失真查找表（LUT）的可变索引方法及其实现。在这种方法中,查找表项的密度与功率放大器非线性程度成比例,与传统LUT地址寻址方法相比,这种方法具有简单、灵活、自适应、易于实现等特点,并在FPGA中成功实现。实现结果表明,这种方法是切实可行的。     

Adaptive predistortion using threshold decomposition‐based piecewise linear modeling

A new adaptive predistortion approach for nonlinear power amplifiers based on the piecewise linear (PWL) approximation of nonlinear functions is presented. The PWL model is obtained using threshold decomposition (TD) of the input‐output characteristics. The TD based PWL model is used to develop a baseband predistorter using both the direct and the indirect learning architectures. The proposed predistorter is proved to provide a better performance in suppressing nonlinear distortion than conventional polynomial predistorters and a reduced hardware complexity as compared to lookup table (LUT) approach. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

A system level implementation strategy and partitioning heuristic for LUT-based applications

Partitioning an application among interacting hardware and software components is an important part of system design. In this paper, we introduce a new implementation strategy and partitioning heuristic, well adapted to applications that are composed of functions that can either be implemented in software or in hardware as lookup tables (LUT). Simulation results are presented to show the performance and speedup that the method can achieve.     

基于SoPC的二维IDCT分布式算法的IP核研究

研究基于SOPC的视频解码系统中二维IDCT硬件设计与实现.针对二维IDCT的运算量大、乘法运算多,导致占用FPGA资源多和系统速度慢等问题,其设计采用-维IDCT复用,研究分布式算法实现乘法累加,并使用偏移二进制编码来减小其查找表大小,其直接占用FPGA逻辑单元内的查找表LUT,没有寄存器或内置RAM.综合结果表明,...     

Retrieval of canopy biophysical variables from bidirectional reflectance: Using prior information to solve the ill-posed inverse problem

Estimation of canopy biophysical variables from remote sensing data was investigated using radiative transfer model inversion. Measurement and model uncertainties make the inverse problem ill posed, inducing difficulties and inaccuracies in the search for the solution. This study focuses on the use of prior information to reduce the uncertainties associated to the estimation of canopy biophysical variables in the radiative transfer model inversion process. For this purpose, lookup table (LUT), quasi-Newton algorithm (QNT), and neural network (NNT) inversion techniques were adapted to account for prior information. Results were evaluated over simulated reflectance data sets that allow a detailed analysis of the effect of measurement and model uncertainties. Results demonstrate that the use of prior information significantly improves canopy biophysical variables estimation. LUT and QNT are sensitive to model uncertainties. Conversely, NNT techniques are generally less accurate. However, in our conditions, its accuracy is little dependent significantly on modeling or measurement error. We also observed that bias in the reflectance measurements due to miscalibration did not impact very much the accuracy of biophysical estimation.     

Pipelined Architecture for Multi-String Matching

We present a pipelined approach to hardware implementation of the Aho-Corasick (AC) algorithm for string matching called P-AC. By incorporating pipelined processing, the state graph is reduced to a character trie that only contains forward edges. Edge reduction in P-AC is very impressive and is guaranteed algorithmically. For a signature set with 4434 strings extracted from the Snort rule set, the memory cost of P-AC is only 21.5 bits/char. The simplicity of the pipeline control plus the availability of 2-port memories allow us to implement two pipelines sharing the set of lookup tables on the same device. By doing so, the system throughput can be doubled with little overhead. The throughput of our method is up to 8.8 Gbps when the system is implemented using 550MHz FPGA.     

An Efficient Design of Variable Length Decoder for MPEG-1/2/4

In this paper, a novel and area-efficient variable length decoder (VLD) for MPEG-1/2/4 is presented. Instead of carrying out every variable length coding table with one dedicated lookup table (LUT) directly, we employ an efficient clustering-merging technique to reduce both the size of a single LUT and the total number of LUTs required for MPEG-1/2/4. Synthesis results show that our VLD occupies 10666 gate counts and operates at 125 MHz by using the standard cell from Artisan TSMC's 0.18 $mu{rm m}$ process. As demonstrated, the proposed design outperforms other VLDs with less hardware cost. It can decode a symbol of different standards in every cycle and support video resolution of HD1080 at 30 frames/s for MPEG-1/2/4 real-time decoding.      

Speedup of color palette indexing in self-organization of Kohonen feature map

Based on the self-organization of Kohonen feature map (SOFM), recently, Pei et al. presented an efficient color palette indexing method to construct a color table for compression. Taking the palette indexing method as a representative, this paper presents two new strategies, the pruning-based search strategy and the lookup table (LUT)-based update strategy, to speed up the learning process in the SOFM. Based on four typical testing images, experimental results illustrate that our proposed two strategies have 35% execution-time improvement ratio in average. The practical improvement ratio is very close to that in the theoretical analysis.     

基于多处理机结构的IP路由搜索技术

随着因特网的飞速发展以及128位地址的IPV6的出现,路由表变得日益庞大,这给IP目标地址的查找速度提出了更高的要求。IP地址查询使用的不是精确匹配,而是最长前缀匹配,因查询极其复杂。论文针对现有的IP查询技术的缺点和不足,提出了一种基于多处理器结构的搜索技术,这种技术减少了查找的比较次数和存储空间。