Study on the distribution of DCT residues and its application to R-D analysis of video coding

Quantization errors in discrete-cosine-transform (DCT) video compression are known as DCT residues. Knowledge on their distribution is essential in understanding rate-distortion (R-D) behaviors of generic video coding. Traditional R-D analysis adopted a simplified distortion model. Those distortion models took only quantization parameter into account. They lack adaptability to variation of video sources, as the distribution of coding errors also depends on the statistics of video source. Another common approach models the distribution of DCT residues by fitting experimental data from coded pictures to conjectured statistical distributions, but it did not provide insights into what gives rise to the distribution of DCT residues. This paper intends to quantify the distribution of DCT residues with respect to video source and with respect to the quantization strategy by understanding the quantization of DCT frequency components. Moreover, it is applied to derive an R-D model to show the advantage of the proposed distribution model.     

基于帧DCT变换的鲁棒视频水印算法

为了对数字视频进行版权保护,结合离散余弦变换和数字视频的相关理论,提出了一种基于帧DCT变换的鲁棒视频水印算法.先对水印进行预处理,然后选择嵌入强度,将水印信息多次重复嵌入到视频帧分块DCT变换的中频系数中.提取水印时无须原始视频的参与.实验结果表明,该算法具有较好的不可见性和较强的鲁棒性.     

DCT-based video downscaling transcoder using split and merge technique.

For a conventional downscaling video transcoder, a video server has firstly to decompress the video, perform downscaling operations in the pixel domain, and then recompress it. This is computationally intensive. However, it is difficult to perform video downscaling in the discrete cosine transform (DCT)- domain since the prediction errors of each frame are computed from its immediate past higher resolution frames. Recently, a fast algorithm for DCT domain image downsampling has been proposed to obtain the downsampled version of DCT coefficients with low computational complexity. However, there is a mismatch between the downsampled version of DCT coefficients and the resampled motion vectors. In other words, significant quality degradation is introduced when the derivation of the original motion vectors and the resampled motion vector is large. In this paper, we propose a new architecture to obtain resampled DCT coefficients in the DCT domain by using the split and merge technique. Using our proposed video transcoder architecture, a macroblock is splitted into two regions: dominant region and the boundary region. The dominant region of the macroblock can be transcoded in the DCT domain with low computational complexity and re-encoding error can be avoided. By transcoding the boundary region adaptively, low computational complexity can also be achieved. More importantly, the re-encoding error introduced in the boundary region can be controlled more dynamically. Experimental results show that our proposed video downscaling transcoder can lead to significant computational savings as well as videos with high quality as compared with the conventional approach. The proposed video transcoder is useful for video servers that provide quality service in real-time for heterogeneous clients.     

基于FPGA的二维DCT变换的实现

二维离散余弦变换(DCT)在图像处理和视频编码中起重要的作用。以MPEG 2全I帧编码为背景,在现场可编程门阵列(FPGA)上实现8×8像素的二维DCT变换。算法首先把8×8像素的二维DCT变换化简成8次一维DCT变换加上适当的蝶形运算和顺序重排操作。试验表明,方案可以只用一个一维DCT模块实现输入采样率为74.25MHz的二维DCT变换。     

Zero-quantised discrete cosine transform prediction technique for video encoding

A new analytical model to eliminate redundant discrete cosine transform (DCT) and quantisation (Q) computations in block-based video encoders is proposed. The dynamic ranges of the quantised DCT coefficients are analysed, then a threshold scheme is derived to determine whether the DCT and Q computations can be skipped without video quality degradation. In addition, fast DCT/inverse DCT (IDCT) algorithms are presented to implement the proposed analytical model. The proposed analytical model is compared with other comparable analytical models reported in the literature. Both the theoretical analysis and experimental results demonstrate that the proposed analytical model can greatly reduce the computational complexity of video encoding without any performance degradation and outperforms other analytical models     

一种高清视频低延时远程传输方法

针对远程高清视频传输延迟问题,提出了一种改进的DCT系数量化方法.此方法通过一个自适应取样函数对DCT压缩量化系数进行了分块取样,再对DCT系数重构量化后以百兆以太网的IP包进行实时压缩传输,且接收端通过IDCT变换进行解压,并加入均值为零的噪声处理,解决了图像压缩的块效应问题,从而实现远程实时传输高清视频,满足了民用中对高清视频远程实时传输的要求.     

一种用于实时视频处理的高速二维DCT的电路设计和实现

绝大多数的国际图像和视频压缩标准都采用DCT(离散余弦变换)进行传输编码。本文介绍了一种基于矩阵分解算法的高速实时二维DCT处理器。为了满足视频处理的实时性，整个电路设计中广泛采用了流水线技术，文中详细介绍了二维DCT处理器的电路结构，最后给出了它的FPGA实现。     

A CMOS image sensor with analog two-dimensional DCT-basedcompression circuits for one-chip cameras

This paper presents a CMOS image sensor with on-chip compression using an analog two-dimensional discrete cosine transform (2-D DCT) processor and a variable quantization level analog-to-digital converter (ADC). The analog 2-D DCT processor is essentially suitable for the on-sensor image compression, since the analog image sensor signal can be directly processed. The small and low-power nature of the analog design allows us to achieve low-power, low-cost, one-chip digital video cameras. The 8×8-point analog 2-D DCT processor is designed with fully differential switched-capacitor circuits to obtain sufficient precision for video compression purposes. An imager array has a dedicated eight-channel parallel readout scheme for direct encoding with the analog 2-D DCT processor. The variable level quantization after the 2-D DCT can be performed by the ADC at the same time. A prototype CMOS image sensor integrating these core circuits for compression is implemented based on triple-metal double-polysilicon 0.35-μm CMOS technology. Image encoding using the implemented analog 2-D DCT processor to the image captured by the sensor is successfully performed. The maximum peak signal-to-noise ratio (PSNR) is 36.7 dB     

一种自适应DCT域数字视频水印方案

数字视频广播中的水印一般应当能够在视频编码的同时完成水印的嵌入。针对MPEG2视频压缩编码选用DCT变换进行数据压缩,提出一种自适应DCT域数字视频水印方案,数字水印主要嵌入在视频码流的I帧,嵌入强度和位置根据一定的准则自适应选取。实验结果显示,在不可感知性和鲁棒性方面,自适应方案具有良好性能。     

Motion analysis in 3D DCT domain and its application to video coding

Global, constant-velocity, translational motion in an image sequence induces a characteristic energy footprint in the Fourier-transform (FT) domain; spectrum is limited to a plane with orientation defined by the direction of motion. By detecting these spectral occupancy planes, methods have been proposed to estimate such global motion. Since the discrete cosine transform (DCT) is a ubiquitous tool of all video compression standards to date, we investigate in this paper properties of motion in the DCT domain. We show that global, constant-velocity, translational motion in an image sequence induces in the DCT domain spectral occupancy planes, similarly to the FT domain. Unlike in the FT case, however, these planes are subject to spectral folding. Based on this analysis, we propose a motion estimation method in the DCT domain, and we show that results comparable to standard block matching can be obtained. Moreover, by realizing that significant energy in the DCT domain concentrates around a folded plane, we propose a new approach to video compression. The approach is based on 3D DCT applied to a group of frames, followed by motion-adaptive scanning of DCT coefficients (akin to “zig-zag” scanning in MPEG coders), their adaptive quantization, and final entropy coding. We discuss the design of the complete 3D DCT coder and we carry out a performance comparison of the new coder with ubiquitous hybrid coders.     

Computation reduction for standard-based video encoders based on the energy preservation property of DCT

Based on the energy preservation property of DCT, an optimization technique for motion estimation (ME), DCT, and quantization for standard-based video encoders is developed. First, a stopping criterion for ME is proposed to reduce the number of checking points in finding the motion vectors, and save the computations. The advantage of introducing such a stopping criterion lies in its adaptability to the quantization parameter and applicability to various fast ME algorithms. Then, the DCT and quantization are jointly optimized by tracing the remaining signal energy and removing unnecessary calculations in the process of DCT and quantization. A pruned 2-D DCT based on Huang's fast DCT algorithm is presented to demonstrate the superiority of this algorithm to the full DCT and an existing all-zero block detection method. Although proved to be computationally efficient, the algorithms introduce no obvious quality loss.     

基于H.264/AVC的音视频同步压缩方法

利用H.264/AVC标准中DCT系数的奇偶特性.在编码端将音频比特流嵌入到视频DCT系数中一起压缩传输,在解码端解出视频同时根据相应算法提取出音频信息,从而实现音视频的同步压缩.实验表明该方法在不增加数据量的前提下,可以无失真地还原出音频信号,对视频质量影响很小.     

The quantized DCT and its application to DCT-based video coding

The two-dimensional (2-D) discrete cosine transform (DCT) and the subsequent quantization of the transform coefficients are two computationally demanding steps of any DCT-based video encoder. In this paper, we propose an efficient joint implementation of these two steps, where the precision in computing the DCT can be exchanged for a reduction in the computational complexity. First, the quantization is embedded in the DCT, thus eliminating the need to explicitly quantize the transform coefficients. A multiplierless integer implementation of the quantized DCT (QDCT) is then proposed that performs shift and add operations instead of full multiplications. A sequence of multiplierless QDCT algorithms is obtained with increasing precision and number of computations. Finally, further savings in computations are obtained by terminating the DCT computations whenever intermediate results indicate that the transform and quantization steps will likely result in a block of zero values. The proposed algorithms are applied to, and results are presented for, high-quality MPEG-2 and low bit rate H.263 video encoding.     

An operational rate-distortion optimal single-pass SNR scalablevideo coder

We introduce a new methodology for signal-to-noise ratio (SNR) video scalability based on the partitioning of the DCT coefficients. The DCT coefficients of the displaced frame difference (DFD) for inter-blocks or the intensity for intra-blocks are partitioned into a base layer and one or more enhancement layers, thus, producing an embedded bitstream. Subsets of this bitstream can be transmitted with increasing video quality as measured by the SNR. Given a bit budget for the base and enhancement layers the partitioning of the DCT coefficients is done in a way that is optimal in the operational rate-distortion sense. The optimization is performed using Lagrangian relaxation and dynamic programming (DP). Experimental results are presented and conclusions are drawn     

改进的3D DCT视频编码方案

文中详细研究了离散余弦变换（DCT）的原理及统计特性,提出一种改进的3D DCT的视频编码方案。该算法在不影响信噪比的情况下,运算量减少了1/7,且编码与解码的运算量相当。     

DCT域快速下采样运动向量滤波器

目前的视频压缩标准多数采用DCT变换编码和运动补偿技术。运动估计约占整个编码时间的60％、运动补偿约占10％。所以在视频转码中，运动向量的再使用技术是十分重要的，目前较好的方法是欧氏最小距离方法，它的主要缺点是估计精度不高，本文对此进行了改进，提出了DCT、域快速下采样运动向量滤波器，其重建图像的峰值信噪声比Shanableh等人提出的方法平均高0．2dB。     

基于DCT域的任意分辨率视频可伸缩编码

空间分辨率可伸缩编码能够满足网络视频对不同码率的要求以及不同用户显示终端的需求,成为近几年研究热点.由此提出一种基于DCT域准卷积的任意分辨率下采样方法,该方法通过分析子块与宏块DCT系数之间的关系,实现了由子块DCT系数预测宏块DCT系数,通过低通滤波器截取预测的宏块低频DCT系数,实现任意分辨率下采样.实验证明:该方法适合诸如H.264、AVS等基于DCT变换的视频编码标准,且提供灵活的空间可伸缩能力.     

一种改进的可分级视频编码方法及其网络传输研究

该文提出了一种改进的可分级视频编码方法。为了适应流媒体的分层传输要求,该方法通过对DCT系数量化残差的位平面编码产生视频流的增强层部分,其基本层码流由更多的子基本层组成,各子基本层通过宏块级DCT系数重排及VLC重组生成。同时,该文设计了一种针对该分层视频流数据的网络传输自适应不等重丢包保护(AUPLP)策略,在估计当前可利用带宽资源的基础上,实时调整不同层数据的保护力度,并控制传输截断的层数。仿真结果表明,与传统方法相比该文方案在低带宽时可获得平均1.2dB的编码增益,AUPLP的应用也大大改善了视频流媒体的传输质量。     

Low bit-rate video coding with spatio-temporal geometric transforms

A low bit-rate video coding technique that uses spatio-temporal geometric transforms is presented. Motion compensation based on the bilinear transform is employed to reduce the temporal redundancy of the video. The spatial redundancy of the motion compensated error images is reduced by a combination of fractals and the DCT. It is shown that in the objects boundaries of the motion compensated error image fractals outperforms the DCT, while in the smooth areas the DCT is better than fractals. A hybrid combination of fractals and the DCT gives the best result. The performance of this hybrid codec with geometrically transformed motion compensation is compared against the H.261 standard video codec at 64 kbit/s     

基于NEDA算法的二维DCT硬件加速器的设计实现

应用二维DCT的图像压缩系统,DCT的运算量较大,为了突破该瓶颈,设计了基于NEDA算法的DCT硬件加速器,该设计方案采用移位相加代替乘法运算,并用RAM代替ROM,有效地节省了硬件资源.给出了Verilog仿真结果,结果表明该加速器可以在使用资源非常少的情况下,正确地实现二维DCT运算,适合于各种视频图像压缩方面的应用.