Rate Control Algorithms for Non-Embedded Wavelet-Based Image Coding

During the last decade, there has been an increasing interest in the design of very fast wavelet image encoders focused on specific applications like interactive real-time image and video systems, running on power-constrained devices such as digital cameras, mobile phones where coding delay and/or available computing resources (working memory and power processing) are critical for proper operation. In order to reduce complexity, most of these fast wavelet image encoders are non-(SNR)-embedded and as a consequence, precise rate control is not supported. In this work, we propose some simple rate control algorithms for these kind of encoders and we analyze their impact to determine if, despite their inclusion, the global encoder is still competitive with respect to popular embedded encoders like SPIHT and JPEG2000. In this study we focus on the non-embedded LTW encoder, showing that the increase in complexity due to the rate control algorithm inclusion, maintains LTW competitive with respect to SPIHT and JPEG2000 in terms of R/D performance, coding delay and memory consumption.     

基于人眼视觉特性的三维小波变换视频质量评价方法

视频质量评价(VQA)的研究对于视频系统的发展起 到重要作用。为了更有效地分析评价视频系统性能,本文提出了一种结合人眼视觉特性的三 维小波变换(3D-DWT)客观VQA方法。首先利用3D-DWT对视频中各帧组(GoF)序列进行分解; 计算分解产生的各子带序列质量并将其筛选组合得到GoF质量;再结合时域人眼视 觉特性,利用各GoF的平均亮度以及运动剧烈程度等特征对各GoF质量进行加权组合,得到最 终的视频质 量。本文方法利用了3D-DWT进行视频时域特征的表述,在一定程度上解决了VQA时 域信息描 述困难的问题。在LIVE视频数据库上的实验结果表明,本文评价方法对于视频数据库中所有 失真视频评价 结果与其主观质量的线性相关系数(LCC)值在0.8以上,Spearma n等级相关系数(SROCC)值在0.79以上。与 已有相关方法相比,所提出方法更接近于主观测试结果,具有更好的评价性能。     

Encoder adaptable difference detection for low power video compression in surveillance system

As a state-of-the-art video compression technique, H.264/AVC has been deployed in many surveillance cameras to improve the compression efficiency. However, it induces very high coding complexity, and thus high power consumption. In this paper, a difference detection algorithm is proposed to reduce the computational complexity and power consumption in surveillance video compression by automatically distributing the video data to different modules of the video encoder according to their content similarity features. Without any requirement in changing the encoder hardware, the proposed algorithm provides high adaptability to be integrated into the existing H.264 video encoders. An average of over 82% of overall encoding complexity can be reduced regardless of whether or not the H.264 encoder itself has employed fast algorithms. No loss is observed in both subjective and objective video quality.     

Video encoder optimisation based on energy reservation property of DCT

To reduce the computational complexity for standard-based video encoders, an optimisation technique based on the energy reservation property of discrete cosine transform (DCT) is proposed and applied to both motion estimation and DCT. While proved to be computationally efficient, the algorithms introduce no obvious quality loss and can be easily embedded in an existing video encoder.     

Design of parallel fault-secure encoders for systematic cyclic block transmission codes

In this paper, we consider the problem of designing parallel fault-secure encoders for various systematic cyclic linear codes used in data transmission. It is assumed that the data to be encoded before transmission are stored in a fault-tolerant RAM memory system protected against errors using a cyclic linear error detecting and/or correcting code. The main idea relies on taking advantage of the RAM check bits to control the correct operation of the cyclic code encoder as well. A slightly modified encoder allows not only for encoding the transmission data stream but also, independently and in parallel, to generate the reference check bits which allow for concurrent error detection in the encoder itself. The error detection capacity proves to be effective and grants good levels of protection as shown by error injection campaigns on encoders for various standard linear cyclic error detecting and error correcting codes. Moreover, the complexity evaluation of the FPGA implementations of the encoders shows that their fault-secure versions compare favorably against the unprotected ones, both with respect to hardware complexity and the maximal frequency of operation.     

Efficient Multi-rate Encoder of QC-LDPC Codes Based on FPGA for WIMAX Standard

An efficient multi-rate encoder for IEEE 802.16e LDPC codes which outperforms current single rate encoders with acceptable hardware consumption and effi-cient memory consumption is proposed. This design uti-lizes the common dual-diagonal structure in parity matri-ces to avoid the inverse matrix operation which requires extensive computations. Parallel Matrix-vector multipli-cation (MVM) units, bidirectional operation and storage compression are applied to this multi-rate encoder to in-crease the encoding speed and significantly reduce the quantity of memory bits required. The proposed encoding architecture also contributes to the design of multi-rate encoders whose parity matrices are dual-diagonally struc-tured and have an Approximately lower triangular (ALT) form, such as in IEEE 802.11n and IEEE 802.22. Simu-lation results verified that the proposed encoder can effi-ciently work for all code rates specified in WIMAX stan-dard. With a maximum clock frequency of 117 MHz, the encoder achieves 3 to 10 times higher throughput than prior works. The proposed encoder is capable to switch among six rates by adjusting the input parameter and it achieves the throughput up to 1Gbps.     

An analysis on optimal rates of BDB encoders for RLL and MTR systems

In most recording channels, modulation codes are employed to transform user data to sequences that satisfy some desirable constraint. Run-length-limited (RLL(d,k)) and maximum transition run (MTR(j,k)) systems are examples of constraints that improve timing and detection performance. A modulation encoder typically takes the form of a finite-state machine. Alternatively, a look-ahead encoder can be used instead of a finite-state encoder to reduce complexity. Its encoding process involves a delay called look-ahead. If the input labeling of a look-ahead encoder allows block decodability, the encoder is called a bounded-delay-encodable block-decodable (BDB) encoder. These classes of encoders can be viewed as generalizations of the well-known deterministic and block-decodable encoders. Other related classes are finite-anticipation and sliding-block decodable encoders. In this paper, we clarify the relationship among these encoders. We also discuss the characterization of look-ahead and BDB encoders using the concept of path-classes. To minimize encoder complexity, look-ahead is desired to be small. We show that for nonreturn to zero inverted (NRZI) versions of RLL|,(0,k),RLL(1,k), and RLL(d,infin), a BDB encoder does not yield a higher rate than an optimal block-decodable encoder. However, for RLL(d,k) such that dges4 and d+2lesk相似文献   

Convolutional codes I: Algebraic structure

A convolutional encoder is defined as any constant linear sequential circuit. The associated code is the set of all output sequences resulting from any set of input sequences beginning at any time. Encoders are called equivalent if they generate the same code. The invariant factor theorem is used to determine when a convolutional encoder has a feedback-free inverse, and the minimum delay of any inverse. All encoders are shown to be equivalent to minimal encoders, which are feedback-free encoders with feedback-free delay-free inverses, and which can be realized in the conventional manner with as few memory elements as any equivalent encoder, Minimal encoders are shown to be immune to catastrophic error propagation and, in fact, to lead in a certain sense to the shortest decoded error sequences possible per error event. In two appendices, we introduce dual codes and syndromes, and show that a minimal encoder for a dual code has exactly the complexity of the original encoder; we show that systematic encoders with feedback form a canonical class, and compare this class to the minimal class.     

一种MPEG4标准的快速及高效视频编码器

提出了一个基于MPEG4的快速高效存储的DCT视频编码器，用他把一个H．261视频数据流转换为一个低比特率、低空间分辨率的MPEG4流，并进行无线视频处理。和现有编码器相比，他不仅能够大大地节省实际需要存储空间，计算复杂度也降低了许多，实验结果表明设计的编码器得到的视频质量与象素领域方法得到的视频质量相当。     

Refreshment need metrics for improved shape and texture object-based resilient video coding

Video encoders may use several techniques to improve error resilience. In particular, for video encoders that rely on predictive (inter) coding to remove temporal redundancy, intra coding refreshment is especially useful to stop error propagation when errors occur in the transmission or storage of the coded streams, which can cause the decoded quality to decay very rapidly. In the context of object-based video coding, the video encoder can apply intra coding refreshment to both the shape and the texture data. In this paper, shape refreshment need and texture refreshment need metrics are proposed which can be used by object-based video encoders, notably MPEG-4 video encoders, to determine when the shape and the texture of the various video objects in the scene should be refreshed in order to improve the decoded video quality, e.g., for a given bit rate.     

DCT-Domain Embedded Memory Compression for Hybrid Video Coders

Hybrid video compression schemes such as MPEG2 and H.263 use an image memory for motion-compensated coding. In VLSI implementations, this image is usually stored in external RAM because of its large size. To reduce the overall system costs, we propose to compress the image by a factor of 4 to 5 before storage, which then enables embedding of the image memory on the encoder IC itself. The proposed encoder architecture remains in the DCT-domain, so motion estimation and compensation are now performed from this domain. To control and guarantee the actual storage, scalable compression is used. A hardware implementation is feasible and worthwhile compared to traditional encoders with no noticeable loss in performance.     

Distributed Monoview and Multiview Video Coding

Growing percentage of the world population now uses image and video coding technologies on a regular basis. These technologies are behind the success and quick deployment of services and products such as digital pictures, digital television, DVDs, and Internet video communications. Today's digital video coding paradigm represented by the ITU-T and MPEG standards mainly relies on a hybrid of block- based transform and interframe predictive coding approaches. In this coding framework, the encoder architecture has the task to exploit both the temporal and spatial redundancies present in the video sequence, which is a rather complex exercise. As a consequence, all standard video encoders have a much higher computational complexity than the decoder (typically five to ten times more complex), mainly due to the temporal correlation exploitation tools, notably the motion estimation process. This type of architecture is well-suited for applications where the video is encoded once and decoded many times, i.e., one-to-many topologies, such as broadcasting or video-on-demand, where the cost of the decoder is more critical than the cost of the encoder.     

视频编码中的块运动估计算法分析（一）

在视频压缩的一些国际标准，如Ｈ．２６１．Ｈ．２６３．ＭＰＥＧ１．ＭＰＥＧ２．ＨＤＴＶ中，视频系统编码器的复杂性最主要取决于运动估计。本文以ＭＰＥＧ２编码为例，通过计算机模拟实验，得出了一些常用运动估计算法的对比实验结果，以及常用的几种匹配函数时的对比实验结果。     

一种高效视频编码器的设计

提出了一个基于MPEG-4的快速高效存储的DCT视频编码器的设计原理,用它把一个H.261视频数据流转换为一个低比特率、低空间分辨率的MPEG-4流,并进行无线视频处理.和现有编码器相比,它不仅能够大大节省实际需要的存储空间,计算复杂度也降低了许多,实验结果表明,编码器得到的视频质量与像素领域方法得到的视频质量相当.     

All-Optical Analog-to-Digital Conversion Using Split-and-Delay Technique

We propose a simplified configuration of all-optical analog-to-digital (A/D) conversion using nonlinear optical loop mirrors (NOLMs). While the conventional scheme of such all-optical A/D conversion requires encoders and threshold, for -bit resolution, the proposed configuration realizes an -bit resolution only using a single encoder and threshold, based on a split-and-delay technique, in which the encoder and the threshold operate more than times as fast as the sampling speed. After discussing detailed design issues of the NOLM-based encoder with particular emphasis on the so-called counterpropagating effects, all-optical 3-bit A/D conversion at 10 GS/s is experimentally demonstrated using the proposed configuration.     

An adaptive congestion control scheme for real time packet videotransport

We show that modulating the source rate of a video encoder based on congestion signals from the network has two major benefits: the quality of the video transmission degrades gracefully when the network is congested and the transmission capacity is used efficiently. Source rate modulation techniques have been used in the past in designing fixed rate video encoders used over telephone networks. In such constant bit rate encoders, the source rate modulation is done using feedback information about the occupancy of a local buffer. Thus, the feedback information is available instantaneously to the encoder. In the scheme proposed, the feedback may be delayed by several frames because it comes from an intermediate switching node of a packet switched network. The paper shows the proposed scheme performs quite well despite this delay in feedback. We believe the use of such schemes will simplify the architecture used for supporting real time video services in future nationwide gigabit networks     

一种基于硬件实现的快速运动估计半像素级搜索算法

研究了在绝对差和准则下的整像素级块匹配和半像素级块匹配的联系，对绝对差和进行了合理的数学曲线拟合，通过数学曲线来预测最小绝对差和所在半像素位置，从而得到半像素级最佳匹配矢量。分析了三种不同的凹函数预测模型，提出了一种适合硬件实现的运动估计快速半像素级搜索算法。该算法直接根据整像素级运动估计的结果来推算半像素级运动估计结果，在很大程度上降低了半像素级运动估计的运算复杂度，从而利用低码率视频编码的实时实现。试验结果表明该算法可获得较好的重建图像质量。该算法利于硬件实现，可以方便地集成到现有的视频编码器中，具有较好的实用价值。     

Art of constructing low-complexity encoders/decoders forconstrained block codes

A rate p : q block encoder is a dataword-to-codeword assignment from 2^p p-bit datawords to 2^p q-bit codewords, and the corresponding block decoder is the inverse of the encoder. When designing block encoders/decoders for constrained systems, often, more than 2^p codewords are available. In this paper, as our main contribution, we propose efficient heuristic computer algorithms to eliminate the excess codewords and to construct low hardware complexity block encoders/decoders. For (0,4/4) and (0,3/6) PRML constraints, block encoders/decoders generated using the proposed algorithms are comparable in complexity to human-generated encoders/decoders, but are significantly simpler than lexicographical encoders/decoders     

Online rate control for video streams

A mechanism for varying the frame rate of pre-encoded video clips online is described. The mechanism relies on two different encoders. An offline encoder creates a high-quality bit stream encoded at 30 fps, as well as separate files containing motion vectors for the same clip at lower frame rates. An online encoder decodes the bit stream (if necessary) and re-encodes it at lower frame rates in real time using the precomputed, stored motion information. Online frame rate control, used in conjunction with dynamic bit rate control, allows clients to solve the rate mismatch between the bandwidth available to them and the bit rate of the pre-encoded bit stream. Clients can therefore choose the amount of trade-off between temporal and spatial quality while resolving the rate mismatch problem. Moreover, online frame rate control provides a natural means for implementing a VCR-like fast forward control for video streaming applications, without increasing bandwidth consumption.An earlier version of this paper appeared in Proceedings of ACM Multimedia, 1999, pp. 141–144.