On decoding MPEG-4 reversible variable length codes

Recently, Webb presented some efficient indexing methods for decoding reversible variable length codes (RVLCs) which are used to encode MPEG-4 DCT coefficients. Given an RVLC, this paper presents two new indexing methods for decoding the RVLCs of MPEG-4 DCT coefficients. Compromising the time requirement, our proposed decoding methods need the least row memory requirement when compared to Webb's methods.     

On design of error-correcting reversible variable length codes

We propose an algorithm for construction of reversible variable length codes (RVLCs) with good error-correcting properties. The error-correcting properties are evaluated by a metric called the free distance, which is always greater than one in the case of the proposed RVLCs. Since variable length codes (VLCs) typically have free distance equal to one, the proposed RVLCs exhibit significant improvement in symbol error rate relative to VLCs constructed using standard methods.     

Joint source/channel coding for variable length codes

When using entropy coding over a noisy channel, it is customary to protect the highly vulnerable bitstream with an error correcting code. In this paper, we propose a technique which utilizes the residual redundancy at the output of the source coder to provide error protection for entropy coded systems     

Two algorithms for constructing efficient huffman-code based reversible variable length codes

In this paper, Huffman-code based reversible variable length code (RVLC) construction algorithms are studied. We use graph models to represent the prefix, suffix and Hamming distance relationships among RVLC candidate codewords. The properties of the so-obtained graphs are investigated in detail, based on which we present two efficient RVLC construction algorithms: algorithm 1 aims at minimizing the average codeword length while algorithm 2 jointly minimizes the average codeword length and maximizes the error detection probability at the same time.     

Error recovery for variable length codes

When an error occurs in the encoded bit stream produced by a variable length code, the decoder may lose synchronization. A state model for synchronization recovery is developed, and a method for determining the expected span of source symbols lost is presented. The performance of various codes with respect to error recovery is discussed. Two examples are given where equivalent optimal codes have a marked difference in their error recovery characteristics. Some open problems are indicated.     

Reversible variable length codes

Proposes some reversible variable length codes (RVLCs) which can be decoded instantaneously both in the forward and backward directions and have high transmission efficiency. These codes can be used, for example, in the backward reconstruction of video signals from the data last received when some signal is lost midway in the transmission. Schemes for a symmetrical RVLC requiring only a single code table and for an asymmetrical RVLC having short average code length are introduced. They compare favorably with other reversible codes such as B2 codes in several aspects     

Multiple-symbol parallel decoding for variable length codes

In this paper, a multiple-symbol parallel variable length decoding (VLD) scheme is introduced. The scheme is capable of decoding all the codewords in an N-bit block of encoded input data stream. The proposed method partially breaks the recursive dependency related to the VLD. First, all possible codewords in the block are detected in parallel and lengths are returned. The procedure results redundant number of codeword lengths from which incorrect values are removed by recursive selection. Next, the index for each symbol corresponding the detected codeword is generated from the length determining the page and the partial codeword defining the offset in symbol table. The symbol lookup can be performed independently from symbol table. Finally, the sum of the valid codeword lengths is provided to an external shifter aligning the encoded input stream for a new decoding cycle. In order to prove feasibility and determine the limiting factors of our proposal, the variable length decoder has been implemented on an field-programmable gate-array (FPGA) technology. When applied to MPEG-2 standard benchmark scenes, on average 4.8 codewords are decoded per cycle resulting in the throughput of 106 million symbols per second.     

Joint source/channel coding for image transmission with JPEG2000 over memoryless channels.

The high compression efficiency and various features provided by JPEG2000 make it attractive for image transmission purposes. A novel joint source/channel coding scheme tailored for JPEG2000 is proposed in this paper to minimize the end-to-end image distortion within a given total transmission rate through memoryless channels. It provides unequal error protection by combining the forward error correction capability from channel codes and the error detection/localization functionality from JPEG2000 in an effective way. The proposed scheme generates quality scalable and error-resilient codestreams. It gives competitive performance with other existing schemes for JPEG2000 in the matched channel condition case and provides more graceful quality degradation for mismatched cases. Furthermore, both fixed-length source packets and fixed-length channel packets can be efficiently formed with the same algorithm.     

JPEG image transmission over mobile network with an efficient channel coding and interleaving

This article studies improving of coloured JPEG image transmission over mobile wireless personal area network through the Bluetooth networks. This article uses many types of enhanced data rate and asynchronous connectionless packets. It presents a proposed chaotic interleaving technique for improving a transmission of coloured images over burst error environment through merging it with error control scheme. The computational complexity of the used different error control schemes is considered. A comparison study between different scenarios of the image transmission is held in to choose an effective technique. The simulation experiments are carried over the correlated fading channel using the widely accepted Jakes’ model. Our experiments reveal that the proposed chaotic interleaving technique enhances quality of the received coloured image. Our simulation results show that the convolutional codes with longer constraint length are effective if its complexity is ignored. It reveals also that the standard error control scheme of old Bluetooth versions is ineffective in the case of coloured image transmission over mobile Bluetooth network. Finally, the proposed scenarios of the standard error control scheme with the chaotic interleaver perform better than the convolutional codes with reducing the complexity.     

Extending the BACIC algorithm for robust transmission over a noisy channel

This study introduces error control to the block arithmetic coding for image compression (BACIC): a new method for lossless bilevel image compression. BACIC can successfully transmit bilevel images when channel bit error rates are as high as 10/sup -3/ while providing compression ratios twice that of G3, the only facsimile standard which incorporates error control into its algorithm.     

Soft decoding and synchronization of arithmetic codes: application to image transmission over noisy channels

The paper addresses the issue of robust and joint source-channel decoding of arithmetic codes. We first analyze dependencies between the variables involved in arithmetic coding by means of the Bayesian formalism. This provides a suitable framework for designing a soft decoding algorithm that provides high error-resilience. It also provides a natural setting for "soft synchronization", i.e., to introduce anchors favoring the likelihood of "synchronized" paths. In order to maintain the complexity of the estimation within a realistic range, a simple, yet efficient, pruning method is described. The algorithm can be placed in an iterative source-channel decoding structure, in the spirit of serial turbo codes. Models and algorithms are then applied to context-based arithmetic coding widely used in practical systems (e.g., JPEG-2000). Experimentation results with both theoretical sources and with real images coded with JPEG-2000 reveal very good error resilience performances.     

Robust transform image coder over noisy channel

A robust quantiser design for image coding is presented. The proposed quantiser can be viewed as the combination of compound of a quantiser, a variable length code (VLC) coder, and a channel coder. Simulation results show that our proposed scheme has a graceful distortion behaviour within the designed noise range     

Joint source-channel codes based on irregular turbo codes and variable length codes

Variable length codes (VLCs), used in data compression, are very sensitive to error propagation in the presence of noisy channels. To address this problem, several joint sourcechannel turbo techniques have been proposed in the literature. In this paper, we focus on pairs of source/VLC of low redundancy, i.e., when there is a good match between the source statistics and the length distribution of the VLC. It is a case not considered extensively in the literature so far and the classical concatenation of a VLC and a convolutional code is not satisfying. Through EXIT chart and interleaving gain analysis, we show that the introduction of a repetition code between the VLC and the convolutional code considerably improves global performance. In particular, excellent symbol error rates are obtained with reversible VLCs which are used in recent source codecs.     

Construction of efficient error-limiting variable length codes

A novel method for generating an optimal binary prefix condition code is described. The proposed code generation method generates optimal variable length codes that have short average error spans compared to the existing self-synchronising codes. A technique for calculating the expected error spans of variable length codes are also presented     

Soft-input soft-output decoding of variable length codes

We present a method for utilizing soft information in decoding of variable length codes (VLCs). When compared with traditional VLC decoding, which is performed using "hard" input bits and a state machine, the soft-input VLC decoding offers improved performance in terms of packet and symbol error rates. Soft-input VLC decoding is free from the risk, encountered in hard decision VLC decoders in noisy environments, of terminating the decoding in an unsynchronized state, and it offers the possibility to exploit a priori knowledge, if available, of the number of symbols contained in the packet     

Test for synchronizability of finite automata and variable length codes

A finite automation is called synchronizable ofNth order if the knowledge of the lastNoutputs suffices to determine the state of the automaton at one time during the lastNoutputs (including the initial and the final states). In an analogous manner synchronizability ofNth order is defined for variable length codes. The paper describes a test for synchronizability on a more general model, the coding graphs, and shows that finite automata and variable length codes are special cases of it.     

一种可变长码在视频编码中的应用

本文所讨论的一种可逆的可变长码，其码长分布与Golomb-Rice和exp-Golomb编码相同。其编码数据格式能够很好地应用于图像和视频的统计编码中，在保持编码效率的同时，很大程度地提高编码在信道传输中的纠错能力。     

Content-based multiple bitstream image transmission over noisy channels

We propose a novel combined source and channel coding scheme for image transmission over noisy channels. The main feature of the proposed scheme is a systematic decomposition of image sources so that unequal error protection can be applied according to not only bit error sensitivity but also visual content importance. The wavelet transform is adopted to hierarchically decompose the image. The association between the wavelet coefficients and what they represent spatially in the original image is fully exploited so that wavelet blocks are classified based on their corresponding image content. The classification produces wavelet blocks in each class with similar content and statistics, therefore enables high performance source compression using the set partitioning in hierarchical trees (SPIHT) algorithm. To combat the channel noise, an unequal error protection strategy with rate-compatible punctured convolutional/cyclic redundancy check (RCPC/CRC) codes is implemented based on the bit contribution to both peak signal-to-noise ratio (PSNR) and visual quality. At the receiving end, a postprocessing method making use of the SPIHT decoding structure and the classification map is developed to restore the degradation due to the residual error after channel decoding. Experimental results show that the proposed scheme is indeed able to provide protection both for the bits that are more sensitive to errors and for the more important visual content under a noisy transmission environment. In particular, the reconstructed images illustrate consistently better visual quality than using the single-bitstream-based schemes.     

一种JPEG2000图像传输中位平面错误修复算法

JPEG2000图像的编、解码是逐个位平面进行的,因此码流中任何的数据丢失都会影响最后的位平面及对应的小波系数.为了解决这一问题,JPEG2000标准中将错误的小波系数以零替换,但这一替换将影响很多非零系数,造成某些高频成分丢失.本文结合JPEG2000码流的特点提出一种新的错误修复算法.该算法将根据子带间和未损坏的位平面信息来修复损坏的位平面数据.试验结果表明所提出算法比现有算法的信噪比改进1~3个dB.     

Simplified expression for the expected error span recovery for variable length codes

An expression in the form of a series expansion for the error span recovery for variable length codes is presented. Numerical results for both the error span recovery and its standard deviation show complete agreement with those obtained via the complex exact functions. The expression is simple and can be applied to any model where the exact expression is prohibitively complicated.