利用离散余弦变换的语音信号压缩方案

利用离散余弦变换后的语音信号能量主要集中在低频段的特点以及语音信号的短时平稳性，研究三种基于一维离散余弦变换的语音压缩方案。Matlab仿真结果表明三种方案的数据压缩率高，重建语音信号具有艮好的清晰度和自然度。     

DGT与DCT在图像编码中的性能比较

介绍了二维实值离散Gabor变换（RDGT）的快速算法,并着重探讨了二维实值离散Gabor变换与二维离散余弦变换在图像编码中的性能及差异。     

DCT域迭代混合的数字图像水印

提出了基于离散余弦变换和迭代混合的图像水印算法。选取图像DCT域的中频系数,对其运用迭代混合技术嵌入水印,用新的DCT系数置换原来位置的DCT系数。本系统主要包括水印的嵌入、水印的提取和水印的攻击实验三部分,其中水印图像的攻击试验又包括三种攻击试验:椒盐噪声干扰、滤波和剪切攻击,利用这三种攻击来测试水印算法的性能。仿真实验结果表明,该水印算法对于噪声干扰、滤波和剪切攻击都具有较好的鲁棒性,也是图像迭代混合思想成功应用于数字水印方面的一个例子。     

On the discrete cosine transform computation

A generalized signal flow graph for the forward and inverse discrete cosine transform (DCT) based on the Hou's recursive algorithm is described. The regular structure of the generalized signal flow graph enables to realize the DCT and inverse DCT computation for any given N = 2^m, m > 0, and is effectively implementable on a VLSI chip. Computer program for the DCT and inverse DCT computation is also presented.     

基于离散余弦变换和主成分分析的光照条件人脸识别

在光照变化条件下,人脸识别的正确率急剧下降,为了解决该难题,提出了一种离散余弦变换和主成分分析相融合的光照变化条件人脸识别方法.首先对人脸图像进行分块,并采用离散余弦变换对每一个子块提取DCT系数,然后采用主成分分析提取人脸特征,并采用深度学习算法建立人脸识别的分类器,最后采用ORL和Yale B人脸库进行仿真实验,测试其有效性和优越性.实验结果表明,相比其它光照人脸识别方法,本文方法提高了光照人脸图像的识别率,消除了光照变化的不利影响,具有较强的鲁棒性.     

An enhanced technique for online discrete cosine transform-based time-varying delay estimation

Time-delay estimation is developed in the transform domain where discrete cosine transform (DCT) coefficients of time-varying delay signals are estimated. The DCT is very efficient in compacting the signal energy in a small number of coefficients. Hence, the estimation of time-varying delay is obtained through the calculation of a small number of the DCT coefficients. An online maximum likelihood estimator of time-varying delay is developed. The coefficients of the transformed delay signal are obtained by maximizing the likelihood function. When dealing with noisy signals, it is observed that increasing the number of estimated DCT coefficients beyond a certain level does not produce better estimates of the delay signal. This happens because the extra DCT coefficients accommodate the noise present in the received signals.     

离散余弦变换和全息技术相融合的图像压缩感知重构

为了获得理想的图像重构效果,提出一种基于离散余弦变换和全息技术相融合的图像重构算法。首先采用离散余弦变换对图像进行分解保留少数的低频分量,从而构建压缩感知的稀疏基加快重构速度,然后采用全息技术对图像重构结果进行处理,提高图像重构效果,最后采用仿真实验测试算法的性能。实验结果表明,相对于当前经典图像重构算法,本文算法不仅提高了图像重构质量,而且加快了图像重构速度,具有较好的实际应用价值。     

H.264的变换编码和量化过程分析

对H．264协议的变换编码和量化进行了理论分析，给出了具体实现过程，论证了这种变换和量化方式的特点、有效性及应用前景。     

NEW FAST ALGORITHM OF 2-D DISCRETE COSINE TRANSFORM

In this paper, a new algorithm for the fast computation of a 2-D discrete cosine transform (DCT) is presented. It is shown that the N×N DCT, where N = 2m, can be computed using only N 1-D DCT's and additions, instead of using 2N 1-D DCT's as in the conventional row-column approach. Hence the total number of multiplications for the proposed algorithm is only half of that required for the row-column approach, and is also less than that of most of other fast algorithms, while the number of additions is almost comparable to that of others.     

Image encryption based on the finite field cosine transform

In this paper, a novel image encryption scheme is proposed. The technique involves two steps, where the finite field cosine transform is recursively applied to blocks of a given image. In the first step, the image blocks to be transformed result from the regular partition of subimages of the original image. The transformed subimages are regrouped and an intermediate image is constructed. In the second step, a secret-key determines the positions of the intermediate image blocks to be transformed. Besides complying with the main properties required by image encryption methods, the proposed scheme provides benefits related to computational complexity and encoding of the ciphered-images.     

基于DCT和小波的图像和视频编码性能的比较研究

在比较编码性能时,许多人分析了图像和视频编码的离散余弦变换(DCT)和小波变换性能差别,普遍认为图像的小波编码在压缩比和编码质量方面优于传统的DCT变换编码.说明了研究图像和视频压缩算法应当从全面的系统观点来考虑,即把重点放在各要素之间的量化、熵编码和编码系统中的复杂的相互影响的研究上.     

一种无乘法的整数DCT快速实现方法

提出了一种无乘法的整数离散余弦变换(DCT)的实现方法:首先将蝶形运算的浮点数放大为整数,将浮点运算转化成定点的整数运算,然后根据蝶形运算的特点,将蝶形中的乘法转化为基于数值移位和累加的运算过程,从而得到一种通用的快速DCT实现方法.     

一种DCT域多重视频盲水印算法

针对多用户共享版权问题,提出了一种DCT域多重视频盲水印算法.该算法结合Amold置乱及视觉系统特性,通过自适应地调整视频画面绿色分量的DCT系数,实现了不同水印在视频载体中的嵌入.根据视频内容灵活地选择嵌入系数,将经过Arnold置乱的不同图像水印嵌入到视频画面绿色分量的DCT中低频系数里,较好地实现了多重水印在视频载体中的嵌入及盲提取.仿真实验表明,文中算法对常规视频攻击表现出了较好的稳定性,并且具有算法复杂度低及实用性强等特点.     

基于离散小波变换的网络流量多重分形模型

网络流量过程中所蕴含的分形尺度特性对网络性能有显著的影响。因此研究能全面准确地刻画网络流量过程在小时间／空间尺度上的复杂奇异性特征和大时间／空间尺度上的长程依赖性特征的流量模型对Internet网络工程有重要的意义。本文对实测的流量数据(从著名的校园网和国内著名的ISP)进行了分析，利用小波技术构建了一个新的网络流量的多重分形模型，通过模拟验证，发现该新模型能以较简洁的形式捕捉实际网络流量特性，并具有刻画真实流量数据中的多重分形特征的能力。     

基于离散Hartley变换的OFDM实现模型

本文研究离散Hartley变换在OFDM系统中的应用,提出一种基于离散Hartley变换的OFDM实现模型.分析了新模型在加性高斯白噪声信道下的传输性能和算法复杂度.新模型与基于离散傅立叶变换(DFT)的OFDM系统具有相同的传输性能,但计算复杂度降低,时效性提高,且调制与解调算法一致.     

基于小波变换和离散余弦变换的fisher脸识别

本文结合几种现有的人脸识别特征提取算法,先对人脸图像进行小波分解去噪;然后通过离散余弦变换对低频分量作进一步特征提取和压缩,保留人脸图像中对光照、姿态、表情变化不敏感的识别信息;接着利用PCA和LDA相结合得到最终的识别特征;最后采用欧式距离和最近邻分类器识别人脸。实验采用ORL标准人脸库验证了这种组合的有效性。     

一种基于小波变换的灰度数字水印嵌入技术

根据图像小波变换后小波系数的特点,提出了一种新的数字水印嵌入技术。该方法所嵌入的不再是传统的数值序列和二值图像,而是把一幅64×64×8bit的图像作为水印信息嵌入到图像中。实验证明,该水印具有较好的透明性和较好的顽健性。     

A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10⁻³, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.     

基于量化系数均方误差准则的运动估计算法

提出了一种基于量化系数均方误差匹配准则的DCT域运动估计视频编码算法.算法中采用了一种新的运动估计匹配准则,该准则在DCT域内计算逆量化的残差均方误差值.由于该准则已考虑到量化噪声对运动残差能量的影响,因此与传统编码算法相比较,在图像质量基本不变的前提下码率更低.仿真结果显示,基于量化系数均方误差准则的DCT域运动估计算法具有较高的编码效率.