An Electroabsorption Modulator Monolithically Integrated with a Semiconductor Optical Amplifier and a Dual-Waveguide Spot-Size Converter

A semiconductor optical amplifier and electroabsorption modulator monolithically integrated with a spot-size converter input and output is fabricated by means of selective area growth,quantum well intermixing,and asymmetric twin waveguide technology.A 1550～1600nm lossless operation with a high DC extinction ratio of 25dB and more than 10GHz 3dB bandwidth are successfully achieved.The output beam divergence angles of the device in the horizontal and vertical directions are as small as 7.3°×18.0°,respectively,resulting in a 3.0dB coupling loss with a cleaved single-mode optical fiber.     

基于运动矢量统计的同步视频水印算法

通过分析运动矢量的数据统计特性,提出一种基于统计的抗同步攻击视频水印算法.该算法水印信息表示空间与数据特性紧密联系,具有物理空间、时间不可划分性,克服了传统水印算法的检测器对水印同步的依赖性.实验表明,该算法具有很好的鲁棒性和不可感知性,能够抵抗帧删除等同步攻击以及基于视频内容的攻击;在帧删除率小于18%时,水印正确率大于80%.     

"多媒体计算机技术"课程研究型本科教学

研究型本科教学是对传统教学观的发展与创新.在研究型教学实践过程中,可采用基于问题和启发式学习的教学方法.这两种教学方法可以帮助教师培养学生的批判性和创造性思维能力,同时还可以培养学生在实际操作中提出问题、分析问题、解决问题和评价问题的能力.本文结合"多媒体计算机技术"课程教学实践活动,将研究型教学方法应用在本科教学中,对研究型本科教学的内容选择、时间安排进行探索.在内容选择上,以数字水印技术为切入点引入基于启发式的教学方法;在教学手段上以课堂讨论、教师点评的方式进行辅助教学.     

一种基于HVS的空域分块数字水印技术

数字水印作为一种防护技术,在数字产品的保护认证方面越发显得重要,成为当前计算机领域研究的热点问题之一。提出了一种在空域采用分块重复嵌入水印信息和HVS相结合的水印技术。实验结果说明,分块技术在空域的使用提高了水印的嵌入强度和降低计算复杂度,该算法在抵抗旋转、裁剪、缩放方面等有较强能力;水印算法与HVS技术的有效性相结合,数字水印具有很好的掩蔽性。     

基于可见水印的课件版权保护研究

互联网络的快速发展推动了网络课程和远程教育的广泛应用。课件是一种重要的网络教学资源,为保护制作者的权益,将可见水印和可逆数据隐藏技术相结合应用于课件版权保护系统中。版权通告采用了自适应图像特性的可见水印技术,为能按需还原图像采用了基于直方图的可逆数据隐藏技术。该算法使版权水印标识在不影响图像使用的基础上清晰可见,并且可去除水印,完全恢复出原始图像。实验结果验证了该算法应用于课件版权保护的有效性。     

Robust image hash function using local color features

Conventional image hash functions only exploit luminance components of color images to generate robust hashes and then lead to limited discriminative capacities. In this paper, we propose a robust image hash function for color images, which takes all components of color images into account and achieves good discrimination. Firstly, the proposed hash function re-scales the input image to a fixed size. Secondly, it extracts local color features by converting the RGB color image into HSI and YCbCr color spaces and calculating the block mean and variance from each component of the HSI and YCbCr representations. Finally, it takes the Euclidian distances between the block features and a reference feature as hash values. Experiments are conducted to validate the efficiency of our hash function. Receiver operating characteristics (ROC) curve comparisons with two existing algorithms demonstrate that our hash function outperforms the assessed algorithms in classification performances between perceptual robustness and discriminative capability.     

四元数域彩色图像整体式水印算法

该文提出一种结合四元数变换域和四元数分解方法的整体式彩色图像水印算法。首先对彩色载体图像进行分块四元数傅里叶变换得到其频域矩阵,然后对频域单位小块进行四元数奇异值分解,根据分解得到四元数酉矩阵前若干列中对角线元素的幅值构造水印序列,并将水印隐藏到分解得到的实系数奇异值中。仿真实验表明,该文提出的水印方法不仅可以把嵌入水印带来的误差扩散到载体图像的各个颜色分量上,而且比传统的将彩色图像划分为各个单独色彩通道,分别进行水印嵌入的方法不可见性更好,并且,通过构造与奇异值酉矩阵相关的水印序列可以有效解决现有四元数水印算法存在的误检测率以及水印图像易伪造问题。     

单边干涉图相位校正技术与关键问题

基于傅里叶变换红外光谱仪干涉图的单边过零采样和非对称性,对Forman卷积法干涉图相位校正方法进行分析和改进。针对Forman卷积法相位校正过程中需卷积运算,硬件实现难的问题,应用三个快速傅里叶变换(FFT)运算实现线性卷积,节省运算时间。并通过仿真分析了小双边数据量、切趾函数、多次相位校正等对干涉图相位校正效果的影响。在以500K的红外黑体为辐射源,获取红外光谱范围的大气吸收谱实验中,通过HgCdTe点探测器获取单边过零干涉图,采用改进的Forman法对干涉图进行相位校正和光谱重建,经标定、归一化后的复原光谱,光谱分辨率为4cm-1,波长误差比较小,有比较高的准确度。     

基于多级小波分解的复合数字水印检测技术

针对多级小波分解的复合数字水印嵌入技术,为从一个可能已经受到各种图像处理的水印图像中提取水印,提出了一种有效的复合水印提取与检测方法,可充分利用图像的能量分布特征,在高频和低频部分分别提取水印并进行检测.试验证明,该方法有效地保证水印提取的可靠性,具有较好的实用性.     

Layered Access Control Schemes on Watermarked Scalable Media

Intellectual Property (IP) protection is a critical element in multimedia transmission and delivery systems. Conventional IP protection on multimedia data can be categorized into encryption and watermarking. In this paper, a structure to perform layered access control on scalable media by combining encryption and robust watermarking is proposed, implemented, and verified. By taking advantages of the nature of both encryption and watermarking, copyrights of multimedia contents can be well protected and at the same time, multiple-grade services can be provided. In the summated examples, we assume a scalable transmission scheme over the broadcasting environment and use it to test the effectiveness of proposed method. When the embedded watermark is extracted with high confidence, the key to decrypt the next layer can be perfectly recovered. Then, the media contents are reconstructed and the copyrights are assured. The application examples also demonstrate the practicality of the proposed system.