Comparative analysis of bitplane-based wavelet image coders

Wavelet image encoders based on bitplanes give excellent results in the compression of still images. The bitplane concept has recently been generalised to vectors, and wavelet image encoders based on vector bitplanes have been proposed, some achieving slightly better rate /spl times/ distortion performances than scalar encoders. There remains the open question of whether the use of vector bitplanes has the potential of providing more significant rate /spl times/ distortion improvements over scalar versions. The authors address this question by analysing in detail the performance of adaptations, for the use of vector bitplanes, of four popular wavelet-based bitplane encoders. From this analysis, they determine where the gains in performance of encoders based on vector bitplanes come from. It is concluded that performance improvements may come by increasing the vector dimension, provided that codebooks with good packing properties are used.     

A bit allocation scheme for a class of embedded wavelet video encoders

In this paper, we investigate bit allocation strategies for a class of embedded wavelet video encoders. They take advantage of the precise control that such coders have over the bit-rate of each frame. We first show that a piecewise-linear model suits the rate × distortion characteristics of these encoders better than an exponential model, specially in low bit-rate applications. Then, we use an effective iterative procedure for dealing with the problem of frame dependency which yields improved rate × distortion results. Two types of embedded wavelet coders, using scalar and vector quantization, are tested. The results are encouraging, showing that the adoption of an adequate rate-control strategy can improve both objective and subjective quality of video sequences encoded using such embedded wavelet video encoders.     

A high-precision positioning servo-controller using non-sinusoidal two-phase type PLL

Most servomechanisms use encoders whose output signals are 90° phase-shifted sinusoidal waves for detecting angular position. These two-phase signals are not true sinusoidal waves and their distortion makes the positioning accuracy worsen. In this paper, the authors propose non-sinusoidal two-phase type PLL (Phase-Locked Loop) to increase positioning accuracy of servomechanisms. To obtain high-precision detection of angular position, an iterative learning method to compensate the wave distortion was tried, and a high-resolution and high-precision positioning controller that can use low-resolution encoders was obtained. This paper discusses the proposed method and gives experimental results.     

Convergent algorithms for successive approximation vectorquantisation with applications to wavelet image compression

Embedded wavelet coders have become very popular in image compression applications, owing to their simplicity and high coding efficiency. Most of them incorporate some form of successive approximation scalar quantisation. Recently developed algorithms for successive approximation vector quantisation have been shown to be capable of outperforming successive approximation scalar quantisation ones. In the paper, some algorithms for successive approximation vector quantisation are analysed. Results that were previously known only on an experimental basis are derived analytically. An improved algorithm is also developed and is proved to be convergent. These algorithms are applied to the coding of wavelet coefficients of images. Experimental results show that the improved algorithm is more stable in a rate×distortion sense, while maintaining coding performances compatible with the state-of-the-art     

Sliding block encoders that are rho-bar continuous functions of their input (Corresp.)

Sliding block encoders operating within a statistically contaminated source environment are considered. Stationary analog sources are studied using the rho-bar distance as the measure of contamination. Sufficient constructive conditions are developed for the design of sliding block encoders that guarantee rho-bar stability of their output when operating within a statistically contaminated source environment. The relationship of this stability to the robustness of the encoding scheme is discussed, where robustness is a local stability property applied on the output entropy and the average distortion.     

IP网络信源信道联合编码策略

面向IP网络,讨论了一种信源编码的失真估计模型,并用典型的视频编码器作了验证.提出了一种基于包的信道编码方法,并将该方法引入信道编码的失真估计中,对一种信道编码的失真估计模型作了改进.以前述内容为基础,提出了两种信源信道联合编码策略,实验结果表明,这两种策略得到的最优结果在很大程度上提高了视频重建质量.     

Multilevel diversity coding with distortion

In a Diversity Coding System, an information source is encoded by a number of encoders. There are a number of decoders, each of which can access a certain subset of the encoders. We study a diversity coding problem in which there are two levels of decoders. The reconstructions of the source by decoders within the same level are identical, and are subject to the same distortion criterion. Our results imply a principle of superposition when the source consists of two independent data streams. Practical codes achieving zero error can easily be constructed for this special case. A class of open problems on this topic is also suggested     

The partial side information problem with additional reconstructions

We consider a quadratic Gaussian distributed lossy source coding setup with an additional constraint of identical reconstructions between the encoder and the decoder. The setup consists of two correlated Gaussian sources, wherein one of them has to be reconstructed to be within some distortion constraint and match with a corresponding reconstruction at the encoder, while the other source acts as coded side information. We study the trade-off between the rates of two encoders for a given distortion constraint on the reconstruction. An explicit characterization of this trade-off is the main result of the paper. We also give close inner and outer bounds for the discrete memoryless version of the problem.     

Multiterminal source encoding with one distortion criterion

The authors unify earlier investigations concerning the encoding of two correlated sources {X_k}, {Y_k } by means of separate encoders. Decoding is done by a single decoder which receives the outputs from both encoders. The reconstruction of {X_k} is required to be perfect in the usual Shannon sense. The authors determine the admissible rate region R (D), where D is the distortion of the reconstruction of {Y_k}. The binary Hamming case is investigated explicitly     

Adaptive prediction in speech differential encoding systems

The design of speech coders that produce high-quality highly intelligible speech at 6 to 16 kb/s while retaining robustness to background and transmission impairments is an area of current research interest. Differential encoding structures employing adaptive quantization and adaptive prediction constitute one of the most promising approaches to achieving these design objectives. This paper focuses on the design and analysis of adaptive predictors for differential encoders. Several differential encoding systems, including adaptive predictive coding, differential pulse-code modulation, noise feedback coding, direct feedback coding, and prediction error coding, are described and related. Adaptive quantizers are briefly discussed and quantitative and qualitative indicators of speech coder performance are defined. The channel model, the speech model, and the research problem statements used in the design of differential encoders and adaptive predictors are presented. The nomenclature and theory of forward and backward adaptive prediction are developed, and several new backward adaptive algorithms based on various assumptions are presented. A detailed survey of theoretical and simulation results on adaptive prediction for speech differential encoders is given, and the effects of background and transmission impairments on these systems are discussed, Finally, the impact of adaptive predictors on rate distortion theory motivated coders is indicated. Numerous areas for future research are highlighted.     

Multiterminal source coding with high resolution

We consider separate encoding and joint decoding of correlated continuous information sources, subject to a difference distortion measure. We first derive a multiterminal extension of the Shannon lower bound for the rate region. Then we show that this Shannon outer bound is asymptotically tight for small distortions. These results imply that the loss in the sum of the coding rates due to the separation of the encoders vanishes in the limit of high resolution. Furthermore, lattice quantizers followed by Slepian-Wolf lossless encoding are asymptotically optimal. We also investigate the high-resolution rate region in the remote coding case, where the encoders observe only noisy versions of the sources. For the quadratic Gaussian case, we establish a separation result to the effect that multiterminal coding aimed at reconstructing the noisy sources subject to the rate constraints, followed by estimation of the remote sources from these reconstructions, is optimal under certain regularity conditions on the structure of the coding scheme     

LMM-based frame-level rate control for H.264/AVC high-definition video coding

Accurate distribution modeling for the DCT coefficients is greatly important for us to analyze the rate–distortion (R–D) behavior of video encoders. From the experiment, we observed that most of the existing models, paying more attention to the standard-definition (SD) videos, tend not to work well for high-definition (HD) videos. Motivated by this, in this paper, we address the statistical characteristics of DCT coefficients of HD videos coded by H.264/AVC. The contributions of this paper are threefold: first, Laplacian Mixture Model (LMM) is proposed to model the residues instead of using Laplacian or Cauchy distribution; second, the LMM-based analytic rate and distortion models are derived; third, building on the proposed rate and distortion models, a frame-level rate control algorithm is developed. Experimental results show that the proposed rate control method achieves a PSNR improvement of up to 0.85 dB compared with the rate control scheme adopted in the H.264 reference software [1]. Apart from the average visual quality improvement, the temporal visual quality fluctuation is reduced by 17%.     

On RD optimized progressive image coding using JPEG

Among the many different modes of operations allowed in the current JPEG standard, the sequential and progressive modes are the most widely used. While the sequential JPEG mode yields essentially the same level of compression performance for most encoder implementations, the performance of progressive JPEG depends highly upon the designed encoder structure. This is due to the flexibility the standard leaves open in designing progressive JPEG encoders. In this work, a rate-distortion (RD) optimized JPEG compliant progressive encoder is presented that produces a sequence of scans, ordered in terms of decreasing importance. Our encoder outperforms an optimized sequential JPEG encoder in terms of compression efficiency, substantially at low and high bit rates. Moreover, unlike existing JPEG compliant encoders, our encoder can achieve precise rate/distortion control. Substantially better compression performance and precise rate control, provided by our progressive JPEG compliant encoding algorithm, are two highly desired features currently sought for the emerging JPEG-2000 standard.     

Multi Gbit/s bit parallel WDM transmission using dispersion managedfibers

This paper demonstrates the feasibility of a bit parallel WDM (BP-WDM) system using dispersion managed fibers. An expression for the total bit skew as a function of the fiber dispersion and system bandwidth is derived and compared with experimental results. A 4 bit×10 Gbit/s-per bit BP-WDM transmission experiment over 30 km DMF is used and an aggregate bite rate×distance product of 1.2 Tbit/s-km is obtained. The total bit skew of the system is reduced to one half of the bit period. We believe that systems using BPWDM will be useful for computer interconnects in high-speed parallel systems and ring networks     

Robust transmission based on variable-rate error control andgenetic programming

This paper presents a novel variable-rate error control design algorithm matched to full-search vector quantizers (VQs) for robust transmission. In the algorithm, different locations of binary strings obtained from VQ encoders are protected by channel codes with different protection levels. The degree of protection at each location is determined by a genetic programming technique minimizing the end-to-end average distortion of transmission systems. The technique outperforms the equal error protection method. Moreover, as compared with a full search algorithm for optimal unequal error protection, our technique attains comparable performance with significantly lower computational complexities     

Distortion-rate theory for individual sequences

For every individual infinite sequenceuwe define a distortion-rate functiond(R|u)which is shown to be an asymptotically attainable lower bound on the distortion that can be achieved foruby any finite-state encoder which operates at a fixed output information rateR. This is done by means of a coding theorem and its converse. No probabilistic characterization ofuis assumed. The coding theorem demonstrates the existence of {em universal} encoders which are asymptotically optimal for every infinite sequence over a given finite alphabet. The transmission of individual sequences via a noisy channel with a capacityCis also investigated. It is shown that, for every given sequenceuand any finite-state encoder, the average distortion with respect to the channel statistics is lower bounded byd(C|u). Furthermored(C|u)is asymptotically attainable.     

The Hadamard transform-a tool for index assignment

We show that the channel distortion for maximum-entropy encoders, due to noise on a binary-symmetric channel, is minimized if the vector quantizer can be expressed as a linear transform of a hypercube. The index assignment problem is regarded as a problem of linearizing the vector quantizer. We define classes of index assignments with related properties, within which the best index assignment is found by sorting, not searching. Two powerful algorithms for assigning indices to the codevectors of nonredundant coding systems are presented. One algorithm finds the optimal solution in terms of linearity, whereas the other finds a very good, but suboptimal, solution in a very short time     

Nested input-constrained codes

An input-constrained channel, or simply a constraint, is a set S of words that is generated by a finite labeled directed graph. An encoder for S maps, in a lossless manner, sequences of unconstrained input blocks into sequences of channel blocks, the latter sequences being words of S. In most applications, the encoders are finite-state machines and, thus, presented by state diagrams. In the special case where the state diagram of the encoder is (output) deterministic, only the current encoder state and the current channel block are needed for the decoding of the current input block. In this work, the problem of designing coding schemes that can serve two constraints simultaneously is considered. Specifically, given two constraints S₁ and S ₂ such that S₁⊆S₂ and two described rates, conditions are provided for the existence of respective deterministic finite-state encoders ε₁ and ε₂ , at the given rates, such that (the state diagram of) ε₁ is a subgraph of ε₂ Such encoders are referred to as nested encoders. The provided conditions are also constructive in that they imply an algorithm for finding such encoders when they exist. The nesting structure allows to decode ε₁ while using the decoder of ε₂. Developments in optical recording suggest a potential application that can take a significant advantage of nested encoders     

The rate-distortion function for the quadratic Gaussian CEO problem

A new multiterminal source coding problem called the CEO problem was presented and investigated by Berger, Zhang, and Viswanathan. Recently, Viswanathan and Berger have investigated an extension of the CEO problem to Gaussian sources and call it the quadratic Gaussian CEO problem. They considered this problem from a statistical viewpoint, deriving some interesting results. In this paper, we consider the quadratic Gaussian CEO problem from a standpoint of multiterminal rate-distortion theory. We regard the CEO problem as a certain multiterminal remote source coding problem with infinitely many separate encoders whose observations are conditionally independent if the remote source is given. This viewpoint leads us to a complete solution to the problem. We determine the tradeoff between the total amount of rate and squared distortion, deriving an explicit formula of the rate-distortion function. The derived function has the form of a sum of two nonnegative functions. One is a classical rate-distortion function for single Gaussian source and the other is a new rate-distortion function which dominates the performance of the system for a relatively small distortion. It follows immediately from our result that the conjecture of Viswanathan and Berger on the asymptotic behavior of minimum squared distortion for large rates is true