Using binarization and hashing for efficient SIFT matching

The well-known SIFT is capable of extracting distinctive features for image retrieval. However, its matching is time consuming and slows down the entire process. In the SIFT matching, the Euclidean distance is used to measure the similarity of two features, which is expensive because it involves taking square root. Moreover, the scale of the image database is usually too large to adopt linear search for image retrieval. To improve the SIFT matching, this paper proposes a fast image retrieval scheme transforms the SIFT features to binary representations. The complexity of the distance calculation is reduced to bit-wise operation and the retrieval time is greatly decreased. Moreover, the proposed scheme utilizes hashing for retrieving similar images according to the binarized features and further speeds up the retrieval process. The experiment results show the proposed scheme can retrieve images efficiently with only a little sacrifice of accuracy as compared to SIFT.     

SVD-based self-embedding image authentication scheme using quick response code features

Image authentication is a type of technique for the content protection of digital images. This technique is able to detect and locate tampered regions on a digital image. In this paper, two self-embedding image authentication approaches are proposed to involve distinctive singular values. Both of them extract self-characteristics of an image as the crucial authentication information for that image. Subsequently, this information is converted into the two dimensional code format and that codes are then embedded into digital image pixels. With the capability of error correction in two dimensional codes, the extracted authentication data, even being detected with a tamper, still can be completely restored and errorless. As well, it can be utilized to detect whether an image has been tampered with or not. According to experimental results, the proposed approaches are superior to other schemes for images that have been modified to a certain attack extent because the authentication data could be completely extracted in more effective way, and the tampered regions could be identified more accurately. In addition, the proposed approaches utilize these complete self-characteristics to restore tampered regions into their original states.     

OCDMA系统二维QPC地址码的设计和性能研究

通过对光纤信道波长片和时间片的重新组合,提出了一种新的适用于二维OCDMA系统的素数码(2D-QPC)的结构方案;给出了具体的码字设计步骤和过程;运用有限域理论,分析了码字的相关特性.在此基础上,根据"撞击法'研究2D-QPC应用于同步OCDMA系统时的用户容量和误码性能.结果表明:较之一维QPC,2D-QPC的相关特性有了很大的改进,最大自相关旁瓣由1降为0,最大互相关由2降为1;2D-QPC在系统容量上也有很大提高,在相同带宽,传输速率相同的情况下,比一维QPC的系统容量增加p 1倍.     

LDPC码的高性能信道纠错码理论

自从上世纪60年代信道编码理论提出至今,就如何构建一个模拟通信信道容量问题成为了各国学者努力研究的主要课题,并且形成了通信能力体现的一个主要问题。半个世纪以来,各国科学通过构造以两条主线为基础提出的香农条件算法。提出的LDPC码的优异性能吸引人们不断探讨它在各个领域的应用：在宽带接入网中的应用方面,基于二元LDPC的多电平编码计算方法,通过仿真实验证明了该方法在信道传输过程中的高性能算法。在进行算法记录模型方面,用磁记录中的高吞吐率和繁杂LDPC译码方案结合进行。     

一种改进的网络安全信道建立算法

讨论了基于对称加密算法DES的安全信道建立策略．该安全信道能实现通讯双方的认证和加密密钥的协商，并分析了该算法存在的不足。提出了一种改进的安全信道建立算法，新的算法能够承受已知明文攻击，同时还提高了加、解密运算的效率。     

基于结构图设计LDPC码及其性能仿真

提出了使用结构图设计列重为3的正则LDPC校验矩阵。所设计出的校验矩阵具有较大的围长,并且可以改变码长和码率。这些码可以很好的使用在通信和数据存储领域。最后对这些设计出的LDPC码进行了计算机仿真,仿真的数据结果表明:设计出的码在加性白高斯噪声信道下比随机产生的LDPC码有着更为优良的性能。     

异步OCDMA系统素数地址码的设计和分析

在伽罗华有限域理论的基础上,用素域上的二次素数序列对素数码的码函数进行改进.结合MPC和EPC降低互相关值的方法,讨论异步OCDMA系统用户地址码的结构优化.分析MSPC的相关特性:最大互相关为2,最大自相关旁瓣为1,在此基础上,进一步构造出ESPC码字,该码字的自相关旁瓣和互相关的最大值均为1.较之由线性码函数确定的素数码,该码字的峰值旁瓣比大大增加.有利于提高系统传输性能,同时给信号探测提供便利.     

格雷码的反码、补码与带符号格雷码的补码

针对格雷码算法较少的问题,研究了格雷码的求反、取补和带符号格雷码的补码表示.得到了首位取反即为格雷码的反码,再加1即为格雷码的补码的结论.补码表示的带符号格雷码的符号位的权为-1,n位二进制补码符号位的权为-2n-1.这些研究结果将会给格雷码的计算机运算带来方便.     

几何失真景像边缘距离变换匹配的定位精度研究

本文首先建立摄像机高度和姿态发生增量变化时景像几何失真的理论模型，然后对边缘距离变换匹配方法的匹配精度进行了理论分析，导出了边缘距离变换匹配定位精度的解析表达式。     

极化码及性质

主要介绍了基于二元离散无记忆信道的极化码的构造以及相关性质。极化码不但能够在离散对称信道的条件下达到系统的对称容量,而且编译码的复杂度和码字长度几乎呈线性关系,即当码字长度为N时,其复杂度约为O（Nlog N）。最后讨论了极化码的应用以及研究热点。     

基于RS的IP网络视频JSCC策略研究

针对IP网络视频通信中数据分组丢失严重影响视频通信质量的问题,引入具有良好抗分组丢失性能的RS信道编码方法,在深入分析基于RS码的网络环境下的端到端视频传输失真基础上,提出了一种基于RS码的IP网络环境下的网络视频信源信道联合编码(JSCC,joint source channel coding)方案,该方案可以根据当...     

相位编码体制雷达码型选择综合分析

对相位编码体制雷达信号中常用的几种二相编码进行了简要的性能分析;从工程实现的综合性能角度出发,对其中两种比较典型的编码——L序列码和随机序列码的自相关和互相关性进行仿真、分析、比较,提出在实际工程应用中最好选用随机序列码作为相位编码体制雷达的码元。     

红外图像序列的目标增强和检测

文中主要研究了远距离红外图像序列的目标增强和检测问题,提出了基于局部纹理特征的红外图像增强算法,利用红外图像目标和背景区域局部纹理特征的差异来增强目标和背景区域的对比度;为了提高目标检测的速度和精度,利用序列图像的帧间相关信息,采用边检测边跟踪边确认的目标检测方法。实验结果表明,对于远距离、小目标的红外图像,这种增强算法在目标对比度和细节方面都明显优于直方图均衡化方法,而本文采用的目标检测方法仅需很少几帧图像就能检测和跟踪目标,可以在确保目标检测的可靠性的前提下,提高目标的检测速度。     

Turbo码译码算法的比较性分析

在研究MAP，Max—Log—MAP，Log—MAP和SOVA算法原理基础上，通过仿真，对LDg—MAP和SOVA算法进行了比较性分析，同时指出了迭代次数、帧长和信噪比对Turbo码性能的影响。     

Comparing orthonormal matrices for two-dimensional image transform coding by means of the gain distortion function

The gain distortion function is defined as a performance measure for the comparison of orthonormal transforms on the basis of the rate distortion theory. It estimates the number of bits per picture element that can be saved by transform coding. Gain distortion functions were computed for several transforms of the dimension 8 × 8.     

MPEG—4的验证模型及其图象分割技术

即将诞生的ＭＰＥＧ－４，除了其高压缩率外，主要特点是对音视频数据采用基于内容的操作存取及传输，文中阐述了ＭＰＥＧ－４的基于内容的特点，灵活及可扩展的结构形式和有效的开发方式－验证模型法。最后简要介绍实现ＭＰＥＧ－４的关键技术之一的图象分割。     

一种新的二维光正交码的设计及性能分析

以修正二次素数码(MSPC)作为扩时序列,单重合序列(OCS)作为跳频序列,构造了新的二维地址码MSPC/OCS.分析MSPC/OCS的码字性能,得出了互相关均值,并对该码字进行了仿真比较.结果表明,当码重、任意两个相邻"切普"波长的最小间隔一定时,增加跳频码片数,不仅能降低MSPC/OCS码的误码率,还能增加码字容量...     

Color image quality assessment based on sparse representation and reconstruction residual

Image quality assessment (IQA) is a fundamental problem in image processing. While in practice almost all images are represented in the color format, most of the current IQA metrics are designed in gray-scale domain. Color influences the perception of image quality, especially in the case where images are subject to color distortions. With this consideration, this paper presents a novel color image quality index based on Sparse Representation and Reconstruction Residual (SRRR). An overcomplete color dictionary is first trained using natural color images. Then both reference and distorted images are represented using the color dictionary, based on which two feature maps are constructed to measure structure and color distortions in a holistic manner. With the consideration that the feature maps are insensitive to image contrast change, the reconstruction residuals are computed and used as a complementary feature. Additionally, luminance similarity is also incorporated to produce the overall quality score for color images. Experiments on public databases demonstrate that the proposed method achieves promising performance in evaluating traditional distortions, and it outperforms the existing metrics when used for quality evaluation of color-distorted images.