Variable Length Coding Research Articles

Variable-Length Coding with Cost Allowing Non-Vanishing Error Probability

We derive a general formula of the minimum achievable rate for fixed-to-variable length coding with a regular cost function by allowing the error probability up to a constant $\varepsilon$. For a fixed-to-variable length code, we call the set of source sequences that can be decoded without error the dominant set of source sequences. For any two regular cost functions, it is revealed that the dominant set of source sequences for a code attaining the minimum achievable rate with a cost function is also the dominant set for a code attaining the minimum achievable rate with the other cost function. We also give a general formula of the second-order minimum achievable rate.

An information hiding method based on context-based adaptive variable length coding

Current video information hiding algorithms based on H.264 cannot meet the requirement of real-time transmission and get compromise between embedding strength and the changing amplitude of bits stream. To solve these problems, a real-time video information hiding method in CAVLC for H.264/AVC is proposed, which combines information hiding with CAVLC process, and embeds the secret information in the number of trailing coefficients of 4 × 4 macroblocks. Aiming at alleviating video degradation and the embedded secret in real-time transmission, the method is time-efficient and robust. Experimental results show that the embedding process cannot bring detectable video degradation, and only cause a small change in the length of the video stream. Moreover, the embedded secret information can be recovered correctly when being transferred under different RTP lost channels. And the secret information can be extracted directly from the encoded stream without resorting to the original video.

An information hiding method based on context-based adaptive variable length coding

Current video information hiding algorithms based on H.264 cannot meet the requirement of real-time transmission and get compromise between embedding strength and the changing amplitude of bits stream. To solve these problems, a real-time video information hiding method in CAVLC for H.264/AVC is proposed, which combines information hiding with CAVLC process, and embeds the secret information in the number of trailing coefficients of 4 × 4 macroblocks. Aiming at alleviating video degradation and the embedded secret in real-time transmission, the method is time-efficient and robust. Experimental results show that the embedding process cannot bring detectable video degradation, and only cause a small change in the length of the video stream. Moreover, the embedded secret information can be recovered correctly when being transferred under different RTP lost channels. And the secret information can be extracted directly from the encoded stream without resorting to the original video.

STATISTICAL ENCODING FOR IMAGE COMPRESSION BASED ON HIERARCHICAL GRID INTERPOLATION

Algorithms of statistical encoding for image compression are investigated. An approach is proposed to increase the efficiency of variable-length codes when compressing images with losses. An algorithm of statistical encoding is developed for use as part of image compression methods that encode a de-correlated signal with an uneven probability distribution. An experimental comparison of the proposed algorithm with the algorithms ZIP and ARJ is performed while encoding the specific data of the hierarchical compression method. In addition, an experimental comparison of the hierarchical method of image compression, including the developed coding algorithm, with the JPEG method and the method based on the wavelet transform is carried out.

Statistical encoding for image compression based on hierarchical grid interpolation

Algorithms of statistical encoding for image compression are investigated. An approach is proposed to increase the efficiency of variable-length codes when compressing images with losses. An algorithm of statistical encoding is developed for use as part of image compression methods that encode a de-correlated signal with an uneven probability distribution. An experimental comparison of the proposed algorithm with the algorithms ZIP and ARJ is performed while encoding the specific data of the hierarchical compression method. In addition, an experimental comparison of the hierarchical method of image compression, including the developed coding algorithm, with the JPEG method and the method based on the wavelet transform is carried out.

A high-payload, reversible data hiding scheme based on histogram modification in JPEG bitstream

In this paper, we have presented a high-payload, reversible data hiding scheme that is focused on embedding secret data into joint photographic experts group (JPEG) bitstream by using histogram modification. In JPEG, for AC coefficients, 162 different variable length codes (VLCs) are defined and assigned by Huffman coding for all 162 run/size possibilities. After parsing VLC usage in the bitstream, we generated a histogram of run/size. According to a peak point and the nearest zero point of the histogram, the secret data were embedded by modifying the corresponding VLC values slightly. The experimental results and comparing the performance of our scheme with those of other existing schemes demonstrated that the proposed scheme preserved the quality of the image with no distortion and achieved the goal of high embedding capacity.

A Simplified Joint Source and Channel Coding System for Data Transmission over Fading Channel

The major challenge with multimedia communication lies in the demand for higher data rates with better quality of service and lower latency over the wireless channel. Multimedia content is usually source encoded with variable length codes (VLCs) for optimizing bandwidth utilization. VLCs, even though uniquely decodable, suffer from the problem of error propagation. A single bit error can cause an entire block of data to be decoded wrongly, because the ending of a codeword and the beginning of the next can no longer be determined correctly. Several joint source-channel coding (JSCC) techniques are studied in literature to have efficient source coding with resilience to channel errors, but such methods pose a prohibitively high computational complexity. A variant of JSCC for efficient transmission of information is presented in this paper. The information text is encoded by reversible VLC (RVLC) and corresponding to it, a header sequence is generated. Since the headers are critical in decoding a block, they are channel coded with convolution code to protect from errors. Orthogonal frequency division multiplexing is used to provide high data rate communication and robustness to multipath fading. The performance of the system is analysed over Rayleigh fading channel in terms letter error rate (LER) and computational complexity. The proposed method is seen to provide a good LER performance at moderate to high signal to noise ratio, along with minimal computational complexity, when compared with the contemporary JSCC based schemes. Theoretical performance bounds for the error rate of the proposed system are also derived.

Simplified search and construction of capacity‐approaching variable‐length constrained sequence codes

A technique was recently reported to construct high-rate variable-length constrained sequence codes. In this study, the authors outline an algorithm that simplifies the search procedure that is integral to that technique. This algorithm enables examination of a large search space limited only by length and/or number of codewords in order to determine codeword and sourceword lengths that result in high-rate codes. They also describe a straightforward approach to construct codewords and sourcewords of the required lengths in order to complete the design of instantaneously-decodeable capacity-approaching codes that satisfy the specified sequence constraints. They provide results that demonstrate the usefulness of this approach.

Variable length integer codes based on radix number system conversion

A new coding scheme called radix conversion variable length code (RCVLC) is proposed to represent non-negative integers from small values to very large values. RCVLC obtains lowest code length to represent mid-range and large-range integers than Fibonacci code, Elias codes and other existing schemes. This RCVLC is applied as an entropy coder of the Burrows–Wheeler Transform data compressor to compress Calgary corpus which contains both binary and text files. It is observed from the experimental results that the new RCVLC obtains better compression than the existing coding schemes on an average.

Highly Secure and Fast Video Encryption Using Minimum Overhead in H.264/AVC Bitstream

Abstract This paper primarily focuses on the encryption method used to design a selective video encryption scheme to meet following objectives. Encryption and decryption are able to secure in bits-level cryptographic security (after encryption), as well as in the pixel-level visual content security (after decoding for unauthorized user) to meet with sensitive video applications with minimum encryption overhead. It provides perceptual encryption with total scrambling of visual content. Besides, it also makes provision for randomness, not only in spatial but also in the temporal domain. It is presumed that an overall encryption and decryption scheme is quick enough to meet real-time applications. There is no change in the quality of video for genuine users. However, these objectives have been achieved in our proposed algorithm in expense of slight changes in compression bandwidth. The proposed algorithm encrypts residue data and motion vectors after entropy encoding to scramble spatial and temporal resolution. Encryption of motion vectors is based on Expo-Golomb entropy coding in inter-coded macroblock and DC value of residues is encrypted based on context-adaptive variable-length coding (CAVLC) in intra-coded macroblock. In addition, encryption is carried out using an advanced encryption system (AES) in a counter mode stream cipher. The paper deals with security analysis of a proposed scheme in terms of cryptography, as well as perception security.

BASIS OF APPROACH FOR CREATING TECHNOLOGY FOR CYBER DEFENCE OF VIDEO INFORMATION RESOURCES IN THE INFOCOMMUNICATION SPACE

Consider the placing technology of variable length codes in the slots of equal length with modern threats in information and telecommunication systems. Displaying effect distortion variable length codes adopted by the integrity of video information resource. The process of restoration of picture elements if errors in accepted slot. Substantiated conditions for efficient coding in using of slots technology of variable length codes.

A Novel Decode-Aware Compression Technique for Improved Compression and Decompression

With compressed bit streams, more configuration information can be stored using the same memory. The access delay is also reduced, because less bits need to be transferred through the memory interface. To measure the efficiency of bit stream compression, compression ratio (CR) is widely used as a metric. it is a major challenge to develop an efficient compression technique that can significantly reduce the bit stream size without sacrificing the decompression performance. Our approach combines the advantages of previous compression techniques with good compression ratio and those with fast decompression. This paper makes three important contributions. First, it performs smart placement of compressed bit streams to enable fast decompression of variable-length coding. Next, it selects bitmask-based compression parameters suitable for bit stream compression. Finally, it efficiently combines run length encoding and bitmask-based compression to obtain better compression and faster decompression.

Fast H.264 Video Decoding by Bit Order Reversing and Its Application to Real-time H.264 Video Encryption

The demand on fast H.264 video processing technology is highly increasing since the electronics devices with encoding, transmission, and decoding high-resolution video are becoming popular in the consumer market. In this paper, we present a fast H.264 video decoding method by modifying the algorithm dealing with parsing bit-stream of variablelength code (VLC). The key idea of our approach is to reverse the bit order in a fast way through LUT (Look-Up-Table) in order to reduce the bit pattern extraction time for VLC stream. We demonstrated the speedup by employing the proposed idea for H.264 realtime video encryption application. The experimental results show about 11% execution time reduction in the part of video stream parsing function and 3.1% time reduction in the whole video encryption system.

Iterative symbol decoding of variable-length codes with convolutional codes

In this paper, we present a symbol-level iterative source-channel decoding (ISCD) algorithm for reliable transmission of variable-length codes (VLCs). Firstly, an improved source a posteriori probability (APP) decoding approach is proposed for pack-etized variable-length encoded Markov sources. Also proposed is a recursive implementation based on a three-dimensional joint trellis for symbol decoding of binary convolutional codes. APP channel decoding on this joint trellis is realized by modification of the Bahl-Cocke-Jelinek-Raviv algorithm and adaptation to the non-stationary VLC trellis. Simulation results indicate that the proposed ISCD scheme allows to exchange between its constituent decoders the symbol-level extrinsic information and achieves high robustness against channel noises.

A Novel Steganography Technique for SDTV-H.264/AVC Encoded Video

Today, eavesdropping is becoming a common issue in the rapidly growing digital network and has foreseen the need for secret communication channels embedded in digital media. In this paper, a novel steganography technique designed for Standard Definition Digital Television (SDTV) H.264/AVC encoded video sequences is presented. The algorithm introduced here makes use of the compression properties of the Context Adaptive Variable Length Coding (CAVLC) entropy encoder to achieve a low complexity and real-time inserting method. The chosen scheme hides the private message directly in the H.264/AVC bit stream by modifying the AC frequency quantized residual luminance coefficients of intrapredicted I-frames. In order to avoid error propagation in adjacent blocks, an interlaced embedding strategy is applied. Likewise, the steganography technique proposed allows self-detection of the hidden message at the target destination. The code source was implemented by mixing MATLAB 2010 b and Java development environments. Finally, experimental results have been assessed through objective and subjective quality measures and reveal that less visible artifacts are produced with the technique proposed by reaching PSNR values above 40.0 dB and an embedding bit rate average per secret communication channel of 425 bits/sec. This exemplifies that steganography is affordable in digital television.

Joint Selective Encryption of CAVLC and Signs of Motion Vectors for H.264/AVC

Abstract Currently, researchers are orienting their effort to selective encryption in order to protect video sequences against attacks during their transmission over a public channel. The reasons for this trend are of great importance. To reduce video data amount, the video compression chain is essential and to ensure their security, while in transmission, an encryption algorithm is evident. Thus, inserting the encryption module in the video compression chain is better than applying compression and encryption separately in terms of computing time. This paper presents a chaos based encryption method inserted in the H.264 Advanced Video Coding (AVC) used for video conferencing applications. The selective encryption was applied on context adaptive variable length coding (CAVLC) and on the signs of motion vectors. The results were deducted according to the values of peak signal to noise ratio (PSNR), structural similarity (SSIM) and the encryption rate (ER). Combining selective encryption of CAVLC (SE-CAVLC) and motion vector sign encryption (MVSE) are interesting in terms of enhancing the encryption and to damage the visual quality of the decoded video for both Intra and Inter predicted frames.

VLSI –Fuzzy Decision Controller Based ECG Encoder

The electrocardiogram (ECG) is an important biomedical signal and widely used to monitor the function of heart. Continuous remote monitoring of ECG signal of the patients has become necessary nowadays. Since ECG sensors produces large amount of data continuously, it is difficult to store and transmit ECG records. Hence VLSI based data compression techniques are used for low power wireless transmission and transmit more data with limited bandwidth. In this perspective, a novel VLSI (Very Large Scale Integration) based data compression algorithm using fuzzy based decision controller is proposed in which four second order prediction equations had been mathematically formulated based on the present and past 2 samples. In order to select the appropriate equation based on the present, difference of the past samples and slope directions of sample, a fuzzy based decision controller is implemented for encoding. The difference between predicted and original data is encoded and listed in the lookup table. The lookup table maintains a variable length code at every instant to represents a shorter code length for frequently occurring difference values and longer code length for less probable difference values. The proposed method shows an improvement of 2.667 compression ratio, delay, time period and power consumption than the existing system with compromise in the number of logical elements.

Transmission Error Analysis and DC Coefficient Recovery for Compressed Image

ABSTRACTMost of the image coding algorithms like Joint Photographic Expert Group (JPEG), JPEG 2000 use variable length coding (VLC) at last stage of encoder. This VLC makes compressed image transmission more prone to noise. Even a single bit error in the DC coefficients can propagate to other blocks. This paper describes the effect of error occurring at various aspects on the decoded image. This paper proposed modified USO (MUSO) method to recover DC coefficients at post-processing stage of decoding. Simulation results shows that using MUSO method, computational time reduces as well as quality gets improved even at high bit error in AC coefficients.

Implementing Entropy Codec for H.264 Video Compression Standard

Entropy coding is a lossless compression technique which is supported in H.264/AVC standard by different techniques. According to baseline and the extended profiles of H.264/AVC, two variable length techniques are for seen. The first one is context adaptive variable length coding (CAVLC) and the other is exponential Golomb (Exp-Golomb) one. The CAVLC is used to quantize transform residues after reordering them by ZigZag scanning while Exp-Golomb coding is used to quantize other syntax elements. Within the frame of realizing the whole H246 standards, this paper, introduces an implementation of these two codec techniques for baseline profile using Matlab and Simulink. The main concept is to implement CAVLC and Exp-Golomb decoder according to H.264/AVC standard and then device a technique to implement CAVLC & Exp-Golomb encoder. The different implementations are utilized to verify each other.

Zero-Delay and Causal Secure Source Coding

We investigate the combination between causal/zero-delay source coding and information-theoretic secrecy. Two source coding models with secrecy constraints are considered. We start by considering zero-delay perfectly secret lossless transmission of a memoryless source. We derive bounds on the key rate and coding rate needed for perfect zero-delay secrecy. In this setting, we consider two models that differ by the ability of the eavesdropper to parse the bit-stream passing from the encoder to the legitimate decoder into separate messages. We also consider causal source coding with a fidelity criterion and side information at the decoder and the eavesdropper. Unlike the zero-delay setting where variable-length coding is traditionally used but might leak information on the source through the length of the codewords, in this setting, since delay is allowed, block coding is possible. We show that in this setting, a separation of encryption and causal source coding is optimal.