The Experts below are selected from a list of 10458 Experts worldwide ranked by ideXlab platform
Long-wen Chang - One of the best experts on this subject based on the ideXlab platform.
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Designing JPEG quantization tables based on human visual system
Signal Processing: Image Communication, 2001Co-Authors: Ching Yang Wang, Shiuh Ming Lee, Long-wen ChangAbstract:In this paper, we propose a systematic procedure to design a quantization table based on the human visual system model for the baseline JPEG coder. By incorporating the human visual system model with a uniform quantizer, a perceptual quantization table is derived. The quantization table can be easily adapted to the specified resolution for viewing and printing. Experimental results indicate that the derived HVS-based quantization table can achieve better performance in rate-distortion sense than the JPEG default quantization table.
Choy, Tuck C - One of the best experts on this subject based on the ideXlab platform.
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On Dirac Quantisation rules and the trace anomaly
2021Co-Authors: Choy, Tuck CAbstract:In this article I shall clarify various aspects of the Dirac Quantisation rules of 1930\cite{Dirac}, namely (i) the choice of antisymmetric Poisson brackets, (ii) the first Quantisation Rule 1 (iii) the second Quantisation Rule 2, and their relations to the trace anomaly. In fact in 1925 Dirac already had a preliminarily formulation of these rules \cite{Dirac3}. Using them, he had independently rediscovered the Born-Jordan Quantisation rule \cite{BornJordan1925} and called it the quantum condition. This is the best known and undoubtedly most significant of the canonical Quantisation rules of quantum mechanics. We shall discuss several violations of the Poisson-Lie algebra (assumed by Dirac), starting from antisymmetry, which is the first criterion for defining a Lie algebra. Similar violations also occur for the Leibniz's rule and the Jacobi identity, the latter we shall also prove for all our quantum Poisson brackets. That none of these violations jeopardised Dirac's ingenious original derivation \cite{Dirac} of his first Quantisation Rule 1, is quite remarkable. This is because the violations are all of higher orders in $\hbar$. We shall further show that (ii) does not automatically lead to a trace anomaly for certain bounded integrable operators. Several issues that are both pedagogical and foundational arising from this study show that quantum mechanics is still not a finished product. I shall briefly mention some attempts and options to complete its development.Comment: 8 pages no figure
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On Dirac Quantisation rules and the trace anomaly
2020Co-Authors: Choy, Tuck CAbstract:In this article I shall clarify three aspects of the Dirac Quantisation rules of 1931, namely (i) the choice of antisymmetric Poisson brackets, (ii) the first (Poisson bracket) Quantisation rule and finally (iii) the second Dirac Quantisation rule, also known by him as the quantum condition, which is the best known of the canonical Quantisation rules of quantum mechanics. I shall further show that (i) and (ii) do not lead to a trace anomaly for bounded operators, unlike (iii). It is at the final proposed rule (iii) that the trace anomaly emerges. Several issues that are both pedagogical and foundational arising from this study show that quantum mechanics is still not a finished product. I shall discuss options to complete its development.Comment: 8 pages no figure
Ching Yang Wang - One of the best experts on this subject based on the ideXlab platform.
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Designing JPEG quantization tables based on human visual system
Signal Processing: Image Communication, 2001Co-Authors: Ching Yang Wang, Shiuh Ming Lee, Long-wen ChangAbstract:In this paper, we propose a systematic procedure to design a quantization table based on the human visual system model for the baseline JPEG coder. By incorporating the human visual system model with a uniform quantizer, a perceptual quantization table is derived. The quantization table can be easily adapted to the specified resolution for viewing and printing. Experimental results indicate that the derived HVS-based quantization table can achieve better performance in rate-distortion sense than the JPEG default quantization table.
Savvidou Konstantina - One of the best experts on this subject based on the ideXlab platform.
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Gravitational effects in macroscopic quantum systems: a first-principles analysis
2021Co-Authors: Anastopoulos Charis, Lagouvardos Mihalis, Savvidou KonstantinaAbstract:We analyze the weak-field limit of General Relativity with matter and its possible Quantisations. This analysis aims towards a predictive quantum theory to provide a first-principles description of gravitational effects in macroscopic quantum systems. This includes recently proposed experiments on the generation of (Newtonian) gravitational forces from quantum distributions of matter, and phenomena like gravity-induced entanglement, gravitational cat states, gravity-induced Rabi oscillations, and quantum causal orderings of events. Our main results include: (i) The demonstration that these phenomena do not involve true gravitational degrees of freedom. (ii) We show that, unlike full general relativity, weak gravity with matter is a parameterised field theory, i.e., a theory obtained by promoting spacetime coordinates to `dynamical' variables. (iii) Quantisation via gauge-fixing leads to an effective field theory that account for some phenomena, but at the price of spacetime observables becoming ambiguous. This ambiguity is a manifestation of the problem of time that persists even in weak gravity. (iv) A consistent Quantisation of parameterised field theories is essential for a predictive and spacetime covariant theory of weak gravity that describes gravitational effects in macroscopic quantum systems. We also discuss the implication of our results to gravitational decoherence theories, the notion of locality in gravity vis-a-vis quantum information theory, and the intriguing possibility that proposed solutions to the problem of time can be tested in weak-gravity quantum experiments.Comment: 31 page
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Gravitational effects in macroscopic quantum systems: a first-principles analysis
2021Co-Authors: Anastopoulos Charis, Lagouvardos Mihalis, Savvidou KonstantinaAbstract:We analyze the weak-field limit of General Relativity with matter and its possible Quantisations. This analysis aims towards a predictive quantum theory to provide a first-principles description of gravitational effects in macroscopic quantum systems. This includes recently proposed experiments on the generation of (Newtonian) gravitational forces from quantum distributions of matter, and phenomena like gravity-induced entanglement, gravitational cat states, gravity-induced Rabi oscillations, and quantum causal orderings of events. Our main results include: (i) The demonstration that these phenomena do not involve true gravitational degrees of freedom. (ii) We show that, unlike full general relativity, weak gravity with matter is a parameterised field theory, i.e., a theory obtained by promoting spacetime coordinates to `dynamical' variables. (iii) Quantisation via gauge-fixing leads to an effective field theory that account for some phenomena, but at the price of gauge dependence that manifests more strongly on spacetime observables. This ambiguity is a manifestation of the problem of time that persists even in weak gravity. (iv) A consistent Quantisation of parameterised field theories is essential for a predictive and spacetime covariant theory of weak gravity that describes gravitational effects in macroscopic quantum systems. We also discuss the implication of our results to gravitational decoherence theories, the notion of locality in gravity vis-a-vis quantum information theory, and the intriguing possibility that proposed solutions to the problem of time can be tested in weak-gravity quantum experiments.Comment: 35 pages; This new version includes extended interpretational discussions, additional references, and other minor change
N S Lu - One of the best experts on this subject based on the ideXlab platform.
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framework for reducing digital to analogue converter Quantisation error in servo control systems
Iet Control Theory and Applications, 2008Co-Authors: N S LuAbstract:A framework for reducing the digital‐to‐analogue convertor (DAC) Quantisation effect in servo control systems is proposed. In the framework, two compensators are used to shape the spectrum of the DAC Quantisation noise. One compensator, which is an anti-windup-based compensator, not only filters out the high-frequency part of the Quantisation noise, but also provides stability and performance in the presence of control saturation. The other compensator, which is a Quantisation error feedback compensator, provides effective reduction of the low-frequency noise and can account for the spectral distribution of DAC Quantisation noise by an optimal choice of some parameters. Theorems concerning the solvability and the stability are given. Systematic procedures to design the compensators for single-input-single-output (SISO) and multi-input-multi-output (MIMO) plants are also suggested. To validate the performance of the framework, servo control of an optical disc head is considered. Experiments indicate that the output error caused by DAC Quantisation is significantly reduced.
