Block DCT to wavelet transcoding in transform domain

The Discrete Cosine Transform (DCT) to wavelet transcoding provides input for several wavelet-based post-processing techniques of the DCT-coded image/video signals. Transcoding in domain transform avoids inverse transform and retransform operations and saves computation. In this paper, we propose a new technique for transcoding the DCT blocks to wavelet coefficients directly in the transform domain. We perform filtering, IDCT and downsampling operations in a single combined step. The proposed technique achieves the same computational result as that of a spatial domain technique. The transcoding matrices used in the proposed technique are found to satisfy certain symmetric and sparse properties, which are exploited to reduce the computational cost. As the number of zeros in the DCT coefficients is significantly higher compared to the spatial domain, computational cost reduces significantly. Also, with the proposed technique, it is possible to speedup the operation by ignoring some elements in the filtering matrices whose magnitudes are smaller than a threshold value. We demonstrate the application of the proposed transcoding for deblocking of the DCT-coded images in wavelet domain.     

Foveation embedded DCT domain video transcoding

Video transcoding is a key technology to support video communications over heterogeneous networks. Although quite a bit of research effort has been made in video transcoding due to its wide applications, most video transcoding techniques proposed in the literature are optimized based on the simple mean squared error (MSE) metric which does not correlate well with the human visual perception. In this paper, foveation, a property of the HVS, is exploited in video transcoding. The proposed foveation embedded DCT domain video transcoding can reduce the bit rate without compromising visual quality or achieve better subjective quality for a given bit rate by shaping the compression distortion according to the foveated contrast sensitivity function of the HVS. In addition, fast algorithms for video foveation filtering and DCT domain inverse motion compensation are developed, which significantly improve the efficiency of video transcoding.     

Joint image splicing detection in DCT and Contourlet transform domain

Splicing is a fundamental and popular image forgery method and image splicing detection is urgently called for digital image forensics recently. In this paper, a Markov based approach is proposed to detect image splicing. The paper applies the Markov model in the block discrete cosine transform (DCT) domain and the Contourlet transform domain. First, the original Markov features of the inter-block between block DCT coefficients are improved by considering the different frequency ranges of each block DCT coefficients. Then, additional features are extracted in Contourlet transform domain to characterize the dependency of positions among Contourlet subband coefficients. And these features are extracted from single color channel for gray image while extracted from three color channels for color image. Finally, Support Vector Machines (SVMs) are exploited to classify the authentic and spliced images for the gray image dataset while ensemble classifier to the color image dataset. The experiment results demonstrate that the proposed detection scheme outperforms some state-of-the-art methods when applied to Columbia Image Splicing Detection Evaluation Dataset (DVMM), and ranks fourth in phase 1 on the Live Ranking of the first Image Forensics Challenge.     

基于DCT变换的QWT域改进的图像盲水印算法

针对数字图像的版权保护,基于离散余弦变换和四元数小波变换,提出了一种新的改进的盲水印算法,先根据待嵌入水印的大小对载体图像进行四元数小波变换,获得与幅值和相位信息相对应的4幅低频子带,然后对每个低频子带分别进行全局离散余弦变换,最后通过修改两个随机子带中特定位置上DCT系数的大小关系嵌入水印,利用分阶线性Logistic映射产生的混沌序列预处理经Arnold置乱后的水印信息和确定水印的嵌入位置.实验结果表明,该算法对添加噪声、JPEG压缩、滤波和亮度及对比度调整等攻击都具有很强的鲁棒性.     

Wavelet transform domain filters: a spatially selective noisefiltration technique

Wavelet transforms are multiresolution decompositions that can be used to analyze signals and images. They describe a signal by the power at each scale and position. Edges can be located very effectively in the wavelet transform domain. A spatially selective noise filtration technique based on the direct spatial correlation of the wavelet transform at several adjacent scales is introduced. A high correlation is used to infer that there is a significant feature at the position that should be passed through the filter. The authors have tested the technique on simulated signals, phantom images, and real MR images. It is found that the technique can reduce noise contents in signals and images by more than 80% while maintaining at least 80% of the value of the gradient at most edges. The authors did not observe any Gibbs' ringing or significant resolution loss on the filtered images. Artifacts that arose from the filtration are very small and local. The noise filtration technique is quite robust. There are many possible extensions of the technique. The authors see its applications in spatially dependent noise filtration, edge detection and enhancement, image restoration, and motion artifact removal. They have compared the performance of the technique to that of the Weiner filter and found it to be superior.     

Image extraction in DCT domain

More and more digital images are being stored in compressed formats, among which the format using discrete cosine transform (DCT) coefficients is widely adopted (JPEG, MPEG, H.263 etc). To exploit those successful image processing techniques developed in the pixel domain, the authors propose a fast image extraction algorithm to allow images to be extracted directly from compressed DCT coefficients without full decompression. In the proposed technique the extracted images retain quality comparable with that of fully decoded images. However, the computing cost and the storage expense incurred by the proposed algorithm are very much lower than the costs of full decompression. The experiments also demonstrate that the proposed algorithm has tremendous potential in that all existing image processing techniques developed in the pixel domain can be directly applied to compressed images, without involving full decompression.     

基于DCT变换的噪声估计算法

噪声极大地影响了图像视频处理算法的有效性。提出了一种基于DCT变换的自适应噪声估计算法,其采用DCT系数作为块均匀度的度量,较好地适应了高低噪声的情况。此外,算法复杂度不大,能适用于各种实时图像视频处理系统。     

Fast DCT domain filtering using the DCT and the DST

A method for efficient spatial domain filtering, directly in the discrete cosine transform (DCT) domain, is developed and proposed. It consists of using the discrete sine transform (DST) and the DCT for transform-domain processing on the in JPEG basis of the previously derived convolution-multiplication properties of discrete trigonometric transforms. The proposed scheme requires neither zero padding of the input data nor kernel symmetry. It is demonstrated that, in typical applications, the proposed algorithm is significantly more efficient than the conventional filtered spatial domain and earlier proposed DCT domain methods. The proposed method is applicable to any DCT-based image compression standard, such as JPEG, MPEG, and H.261.     

Downsampling versus folding in the DCT domain

Signals can be split into subbands using ideal bandpass filters in the discrete cosine transform (DCT) domain. We show that decimation by band folding is not equivalent to downsampling but results in two convolution operations that involve both the odd and even samples of the signal     

DCT域网格编码矢量量化

本文提出了在离散余弦变换(DCT)域作网格编码矢量量化(TCVQ),并利用量化后相关性的新方法.该方法结合了DCT变换、矢量量化和网格编码量化的优点,它充分利用信号DCT域和时域的相关性来逼近率失真下界,并利用维特比算法来寻找最佳量化序列.同时,它还利用量化后码字间存在的相关性来进一步降低编码率.仿真结果表明,该方法在保持高压缩比的同时具有很高的信噪比性能.在相同编码率下它比全搜索矢量量化(VQ)好1dB左右.同时该方法具有计算量适中,解码简单以及对误差扩散不敏感的优点.     

一种基于DCT变换的语音数字水印算法研究

随着数字媒体的广泛应用,其版权保护也显得日益重要,数字水印(watermarking)近年来引起了人们的高度重视,并逐渐成为多媒体信号处理领域的一个研究热点.本文研究了一种基于DCT变换域的语音数字水印算法,并且为提高算法的安全性,采用线性移位寄存器进行了类似加密的处理.通过实验证明该算法具有较强的稳健性和安全性.     

New polynomial transform algorithm for multidimensional DCT

A new algorithm for the type-II multidimensional discrete cosine transform (MD-DCT) is proposed. Based on the polynomial transform, the rD-DCT with size N₁×N₂×···×N _r, where N_i is a power of 2, can be converted into a series of one dimensional (1-D) discrete cosine transforms (DCTs). The algorithm achieves considerable savings on the number of operations compared with the row-column method. For example, the number of multiplications for computing an r-dimensional DCT is only 1/r times that needed by the row-column method, and the number of additions is also reduced. Compared with other known polynomial transform algorithms for MD-DCT and the most recently presented algorithm for MD-DCT, the proposed one uses about the same number of operations. However, advantages such as better computational structure and flexibility in the choice of dimensional sizes can be achieved     

Wavelet coding method using small block DCT

A novel wavelet image compression method is introduced. The method applies the small block discrete cosine transform to certain parts of the wavelet coefficients before quantisation and coding. Experiments show that the new method achieves good results with only a negligible increase in total complexity     

K-L变换编码与DCT变换编码及其比较

讨论了DCT变换和K－L变换的基本过程，通过便证系统地就两者之间的若干问题进行了比较与分析。     

基于预测编码与DCT变换编码的比较

深入分析了预测编码与DCT变换编码的异同点，并从编码增益、块效应系数、预测与变换与变换前后的能量关系等多方面比较了两种编码的优缺点。     

Robust color image hiding method in DCT domain

Although muchresearch has been devotedto embed agray i mage and binary watermark information into agray cover-i mage or a color cover-i mage[1 ,2],little re-search has been done on inserting a color i mage into acolor cover-i mage.Color i mage is characte…     

Wavelet transform in scattering data interpolation

A fast algorithm for scattering data interpolation is presented. Based on the multiresolution wavelet transform, a preconditioning scheme is proposed to expedite the slow computation speed in the interpolation problem. By applying the wavelet transform before and after any conventional iterative solving method, fast data interpolation can be easily achieved.<>     

基于HVS的DCT域数字水印技术

提出了一种结合HVS的DCT域自适应图像水印算法,该算法根据人类视觉系统的频率、亮度、对比度特点,利用JND阈值自适应地调整要嵌入的水印强度,并根据人类视觉频率响应函数表征的人眼对中频信息敏感度较低频信息敏感度低的特点,把水印信息嵌入到经过DCT变换后的原始图像中频区域,完成数字水印的嵌入。     

Postprocessing technique for blocking artifacts reduction in DCT domain

An effective post-processing technique is proposed to reduce the blocking artifacts in the block discrete cosine transform (BDCT)-coded images. Simulation results indicate that the proposed scheme outperforms conventional post-processing techniques in both PSNR and visual quality.