254 research outputs found
Lower Bounds on the Redundancy of Huffman Codes with Known and Unknown Probabilities
In this paper we provide a method to obtain tight lower bounds on the minimum
redundancy achievable by a Huffman code when the probability distribution
underlying an alphabet is only partially known. In particular, we address the
case where the occurrence probabilities are unknown for some of the symbols in
an alphabet. Bounds can be obtained for alphabets of a given size, for
alphabets of up to a given size, and for alphabets of arbitrary size. The
method operates on a Computer Algebra System, yielding closed-form numbers for
all results. Finally, we show the potential of the proposed method to shed some
light on the structure of the minimum redundancy achievable by the Huffman
code
Improved Sequential MAP estimation of CABAC encoded data with objective adjustment of the complexity/efficiency tradeoff
International audienceThis paper presents an efficient MAP estimator for the joint source-channel decoding of data encoded with a context adaptive binary arithmetic coder (CABAC). The decoding process is compatible with realistic implementations of CABAC in standards like H.264, i.e., handling adaptive probabilities, context modeling and integer arithmetic coding. Soft decoding is obtained using an improved sequential decoding technique, which allows to obtain various tradeoffs between complexity and efficiency. The algorithms are simulated in a context reminiscent of H264. Error detection is realized by exploiting on one side the properties of the binarization scheme and on the other side the redundancy left in the code string. As a result, the CABAC compression efficiency is preserved and no additional redundancy is introduced in the bit stream. Simulation results outline the efficiency of the proposed techniques for encoded data sent over AWGN and UMTS-OFDM channels
Fast, Small and Exact: Infinite-order Language Modelling with Compressed Suffix Trees
Efficient methods for storing and querying are critical for scaling
high-order n-gram language models to large corpora. We propose a language model
based on compressed suffix trees, a representation that is highly compact and
can be easily held in memory, while supporting queries needed in computing
language model probabilities on-the-fly. We present several optimisations which
improve query runtimes up to 2500x, despite only incurring a modest increase in
construction time and memory usage. For large corpora and high Markov orders,
our method is highly competitive with the state-of-the-art KenLM package. It
imposes much lower memory requirements, often by orders of magnitude, and has
runtimes that are either similar (for training) or comparable (for querying).Comment: 14 pages in Transactions of the Association for Computational
Linguistics (TACL) 201
General form of almost instantaneous fixed-to-variable-length codes
A general class of the almost instantaneous fixed-to-variable-length (AIFV)
codes is proposed, which contains every possible binary code we can make when
allowing finite bits of decoding delay. The contribution of the paper lies in
the following. (i) Introducing -bit-delay AIFV codes, constructed by
multiple code trees with higher flexibility than the conventional AIFV codes.
(ii) Proving that the proposed codes can represent any uniquely-encodable and
uniquely-decodable variable-to-variable length codes. (iii) Showing how to
express codes as multiple code trees with minimum decoding delay. (iv)
Formulating the constraints of decodability as the comparison of intervals in
the real number line. The theoretical results in this paper are expected to be
useful for further study on AIFV codes.Comment: submitted to IEEE Transactions on Information Theory. arXiv admin
note: text overlap with arXiv:1607.07247 by other author
Optimality of Huffman Code in the Class of 1-bit Delay Decodable Codes
For a given independent and identically distributed (i.i.d.) source, Huffman
code achieves the optimal average codeword length in the class of instantaneous
code with a single code table. However, it is known that there exist
time-variant encoders, which achieve a shorter average codeword length than the
Huffman code, using multiple code tables and allowing at most k-bit decoding
delay for k = 2, 3, 4, . . .. On the other hand, it is not known whether there
exists a 1-bit delay decodable code, which achieves a shorter average length
than the Huffman code. This paper proves that for a given i.i.d. source, a
Huffman code achieves the optimal average codeword length in the class of 1-bit
delay decodable codes with a finite number of code tables
Adaptive arithmetic data compression: An Implementation suitable for noiseless communication channel use
Noiseless data compression can provide important benefits in speed improvements and cost savings to computer communication. To be most effective, the compression process should be off-loaded from any processing CPU and be placed into a communication device. To operate transparently, It also should be adaptable to the data, operate in a single pass, and be able to perform at the communication link\u27s speed. Compression methods are surveyed with emphasis given to how well they meet these criteria. In this thesis, a string matching statistical unit paired with arithmetic coding, is investigated in detail. It is implemented and optimized so that its performance (speed, memory use, and compression ratio) can be evaluated. Finally, the requirements and additional concerns for the implementation of this algorithm into a communication device are addressed
Contributions in image and video coding
Orientador: Max Henrique Machado CostaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: A comunidade de codificação de imagens e vídeo vem também trabalhando em inovações que vão além das tradicionais técnicas de codificação de imagens e vídeo. Este trabalho é um conjunto de contribuições a vários tópicos que têm recebido crescente interesse de pesquisadores na comunidade, nominalmente, codificação escalável, codificação de baixa complexidade para dispositivos móveis, codificação de vídeo de múltiplas vistas e codificação adaptativa em tempo real. A primeira contribuição estuda o desempenho de três transformadas 3-D rápidas por blocos em um codificador de vídeo de baixa complexidade. O codificador recebeu o nome de Fast Embedded Video Codec (FEVC). Novos métodos de implementação e ordens de varredura são propostos para as transformadas. Os coeficiente 3-D são codificados por planos de bits pelos codificadores de entropia, produzindo um fluxo de bits (bitstream) de saída totalmente embutida. Todas as implementações são feitas usando arquitetura com aritmética inteira de 16 bits. Somente adições e deslocamentos de bits são necessários, o que reduz a complexidade computacional. Mesmo com essas restrições, um bom desempenho em termos de taxa de bits versus distorção pôde ser obtido e os tempos de codificação são significativamente menores (em torno de 160 vezes) quando comparados ao padrão H.264/AVC. A segunda contribuição é a otimização de uma recente abordagem proposta para codificação de vídeo de múltiplas vistas em aplicações de video-conferência e outras aplicações do tipo "unicast" similares. O cenário alvo nessa abordagem é fornecer vídeo com percepção real em 3-D e ponto de vista livre a boas taxas de compressão. Para atingir tal objetivo, pesos são atribuídos a cada vista e mapeados em parâmetros de quantização. Neste trabalho, o mapeamento ad-hoc anteriormente proposto entre pesos e parâmetros de quantização é mostrado ser quase-ótimo para uma fonte Gaussiana e um mapeamento ótimo é derivado para fonte típicas de vídeo. A terceira contribuição explora várias estratégias para varredura adaptativa dos coeficientes da transformada no padrão JPEG XR. A ordem de varredura original, global e adaptativa do JPEG XR é comparada com os métodos de varredura localizados e híbridos propostos neste trabalho. Essas novas ordens não requerem mudanças nem nos outros estágios de codificação e decodificação, nem na definição da bitstream A quarta e última contribuição propõe uma transformada por blocos dependente do sinal. As transformadas hierárquicas usualmente exploram a informação residual entre os níveis no estágio da codificação de entropia, mas não no estágio da transformada. A transformada proposta neste trabalho é uma técnica de compactação de energia que também explora as similaridades estruturais entre os níveis de resolução. A idéia central da técnica é incluir na transformada hierárquica um número de funções de base adaptativas derivadas da resolução menor do sinal. Um codificador de imagens completo foi desenvolvido para medir o desempenho da nova transformada e os resultados obtidos são discutidos neste trabalhoAbstract: The image and video coding community has often been working on new advances that go beyond traditional image and video architectures. This work is a set of contributions to various topics that have received increasing attention from researchers in the community, namely, scalable coding, low-complexity coding for portable devices, multiview video coding and run-time adaptive coding. The first contribution studies the performance of three fast block-based 3-D transforms in a low complexity video codec. The codec has received the name Fast Embedded Video Codec (FEVC). New implementation methods and scanning orders are proposed for the transforms. The 3-D coefficients are encoded bit-plane by bit-plane by entropy coders, producing a fully embedded output bitstream. All implementation is performed using 16-bit integer arithmetic. Only additions and bit shifts are necessary, thus lowering computational complexity. Even with these constraints, reasonable rate versus distortion performance can be achieved and the encoding time is significantly smaller (around 160 times) when compared to the H.264/AVC standard. The second contribution is the optimization of a recent approach proposed for multiview video coding in videoconferencing applications or other similar unicast-like applications. The target scenario in this approach is providing realistic 3-D video with free viewpoint video at good compression rates. To achieve such an objective, weights are computed for each view and mapped into quantization parameters. In this work, the previously proposed ad-hoc mapping between weights and quantization parameters is shown to be quasi-optimum for a Gaussian source and an optimum mapping is derived for a typical video source. The third contribution exploits several strategies for adaptive scanning of transform coefficients in the JPEG XR standard. The original global adaptive scanning order applied in JPEG XR is compared with the localized and hybrid scanning methods proposed in this work. These new orders do not require changes in either the other coding and decoding stages or in the bitstream definition. The fourth and last contribution proposes an hierarchical signal dependent block-based transform. Hierarchical transforms usually exploit the residual cross-level information at the entropy coding step, but not at the transform step. The transform proposed in this work is an energy compaction technique that can also exploit these cross-resolution-level structural similarities. The core idea of the technique is to include in the hierarchical transform a number of adaptive basis functions derived from the lower resolution of the signal. A full image codec is developed in order to measure the performance of the new transform and the obtained results are discussed in this workDoutoradoTelecomunicações e TelemáticaDoutor em Engenharia Elétric
Compression algorithms for biomedical signals and nanopore sequencing data
The massive generation of biological digital information creates various computing
challenges such as its storage and transmission. For example, biomedical
signals, such as electroencephalograms (EEG), are recorded by multiple sensors over
long periods of time, resulting in large volumes of data. Another example is genome
DNA sequencing data, where the amount of data generated globally is seeing explosive
growth, leading to increasing needs for processing, storage, and transmission
resources. In this thesis we investigate the use of data compression techniques for
this problem, in two different scenarios where computational efficiency is crucial.
First we study the compression of multi-channel biomedical signals. We present
a new lossless data compressor for multi-channel signals, GSC, which achieves compression
performance similar to the state of the art, while being more computationally
efficient than other available alternatives. The compressor uses two novel
integer-based implementations of the predictive coding and expert advice schemes
for multi-channel signals. We also develop a version of GSC optimized for EEG
data. This version manages to significantly lower compression times while attaining
similar compression performance for that specic type of signal.
In a second scenario we study the compression of DNA sequencing data produced
by nanopore sequencing technologies. We present two novel lossless compression algorithms
specifically tailored to nanopore FASTQ files. ENANO is a reference-free
compressor, which mainly focuses on the compression of quality scores. It achieves
state of the art compression performance, while being fast and with low memory
consumption when compared to other popular FASTQ compression tools. On the
other hand, RENANO is a reference-based compressor, which improves on ENANO,
by providing a more efficient base call sequence compression component. For RENANO
two algorithms are introduced, corresponding to the following scenarios: a
reference genome is available without cost to both the compressor and the decompressor;
and the reference genome is available only on the compressor side, and a
compacted version of the reference is included in the compressed le. Both algorithms
of RENANO significantly improve the compression performance of ENANO,
with similar compression times, and higher memory requirements.La generación masiva de información digital biológica da lugar a múltiples desafíos informáticos, como su almacenamiento y transmisión. Por ejemplo, las señales biomédicas, como los electroencefalogramas (EEG), son generadas por múltiples sensores registrando medidas en simultaneo durante largos períodos de tiempo,
generando grandes volúmenes de datos. Otro ejemplo son los datos de secuenciación de ADN, en donde la cantidad de datos a nivel mundial esta creciendo de forma explosiva, lo que da lugar a una gran necesidad de recursos de procesamiento, almacenamiento y transmisión. En esta tesis investigamos como aplicar técnicas de compresión de datos para atacar este problema, en dos escenarios diferentes donde
la eficiencia computacional juega un rol importante.
Primero estudiamos la compresión de señales biomédicas multicanal. Comenzamos presentando un nuevo compresor de datos sin perdida para señales multicanal, GSC, que logra obtener niveles de compresión en el estado del arte y que al mismo tiempo es mas eficiente computacionalmente que otras alternativas disponibles. El compresor utiliza dos nuevas implementaciones de los esquemas de codificación predictiva
y de asesoramiento de expertos para señales multicanal, basadas en aritmética
de enteros. También presentamos una versión de GSC optimizada para datos de
EEG. Esta versión logra reducir significativamente los tiempos de compresión, sin
deteriorar significativamente los niveles de compresión para datos de EEG.
En un segundo escenario estudiamos la compresión de datos de secuenciación
de ADN generados por tecnologías de secuenciación por nanoporos. En este sentido,
presentamos dos nuevos algoritmos de compresión sin perdida, específicamente
diseñados para archivos FASTQ generados por tecnología de nanoporos. ENANO
es un compresor libre de referencia, enfocado principalmente en la compresión de
los valores de calidad de las bases. ENANO alcanza niveles de compresión en el
estado del arte, siendo a la vez mas eficiente computacionalmente que otras herramientas
populares de compresión de archivos FASTQ. Por otro lado, RENANO es
un compresor basado en la utilización de una referencia, que mejora el rendimiento
de ENANO, a partir de un nuevo esquema de compresión de las secuencias de bases.
Presentamos dos variantes de RENANO, correspondientes a los siguientes escenarios:
(i) se tiene a disposición un genoma de referencia, tanto del lado del compresor
como del descompresor, y (ii) se tiene un genoma de referencia disponible solo del
lado del compresor, y se incluye una versión compacta de la referencia en el archivo
comprimido. Ambas variantes de RENANO mejoran significativamente los niveles
compresión de ENANO, alcanzando tiempos de compresión similares y un mayor
consumo de memoria
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