Browsing by Author "Chang, WT"

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Adaptive interpolator with context modeling in lifting scheme for lossless coding
(2000)
Chang, WT
;
Ho, WJ
;
電信工程研究所
;
Institute of Communications Engineering
Adaptive interpolation with double-interpolator is used for image coding. The double-interpolator means that two adaptive prediction stages are used. The outer loop is an adaptive FIR predictor. The inner loop is an texture based bias estimation. The bias means a content dependent estimated prediction error. By assuming the signals to consist of polynomials of various degrees, the predictor of the outer loop is constructed by linearly combining a set of maximally nat filters. The maximally flat filter is the filtering implementation of the Lagrange interpolation. The prediction is done block by block. Within a block, similar with the lifting scheme, a hierarchical multiresolution prediction is used starting from the fewest resolution 2 by 2 sub-block. The least square prediction error criterion is used to derive the weighting coefficients of the predictor. To further reduce the prediction error, an inner loop to estimate the prediction error is included. Within the inner loop, the pixel to be predicted is classified into groups according to the neighborhood condition. The accumulated mean of the prediction errors of all the pixels within the same group is considered as the bias of the prediction error. This bias is then extracted from the actual prediction error to reduce entropy.
Adaptive predictor based on maximally flat halfband filter in lifting scheme
(1999-11-01)
Ho, WJ
;
Chang, WT
;
電信工程研究所
;
Institute of Communications Engineering
For the complex short time-varying signals, a high-order predictor does not always yield good performance. For this, we investigate the use of a short-order adaptive predictor. Since the maximally flat filters are the optimal predictors for polynomial signal prediction, the adaptation is based on the combination of a set of maximally flat filters. For compression efficiency, the dynamic ranges of the weighting variables are specially considered. For this, based on the Bernstein filters, another form to represent the weighting variables is used. These two sets of weighting coefficients can be transformed into each other with a simple linear transform. Thus, the adaptation can be made in both the time domain and the frequency domain. For block-based image coding, the least square criterion is used to derive the weighting coefficients. Experimental results show that the adaptive predictor performs better than the SSP transform, the median edge detector (MED), and the gradient adjusted predictor (GAP).
Combinative motion estimation algorithm and the corresponding architecture for complex motion phenomenon
(1998-02-01)
Liu, PC
;
Chang, WT
;
Shen, WZ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Combining the features of block matching algorithm and block recursive algorithm a new motion estimation method is proposed for complex motion phenomenon. With the full searching procedure used in block matching algorithm and the adaptive searching procedure used in block recursive algorithm, the proposed combinative algorithm can be used to estimate more complex motion parameters such as translation, zoom, rotation and image deformation and get good performance. To reduce the computational complexity, the corresponding architecture of the combinative algorithm is also proposed. With this architecture the computation amount can be largely reduced to make the proposed algorithm can be used for real time motion estimation.
Creative mechanism design for a prosthetic hand
(2004-11-01)
Chang, WT
;
Tseng, CH
;
Wu, LL
;
機械工程學系
;
Department of Mechanical Engineering
In this paper, an auxiliary methodology called the creative mechanism design is introduced into the innovation of gripping devices for prosthetic hands. This methodology is a systematic approach based on modification of existing devices for the generation of all possible topological structures of mechanisms and mechanical devices. An existing gripping device (Teh Lin ATG-5F prosthetic hand) constructed by a planar six-bar linkage with one degree of freedom is dealt with by using this methodology. Through the processes of generalization, number synthesis, specialization and particularization for the existing design, five new mechanisms are created in this study to apply to anthropomorphic prosthetic hands. The results show that the methodology for creative mechanism design is a powerful tool for creating new categories of mechanisms to avoid existing designs that have patent protection and can help designers in the conceptual phase. Also, this methodology is validated as a useful way to improve prosthetic hands for amputees.
Motion parameter estimation based on the block recursive algorithm with finite word length
(1997-11-01)
Liu, PC
;
Chang, WT
;
Shen, WZ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Three parameter motion model can better describe the motion trajectory of picture element in video sequence. Combining the features of block process and recursive estimation, a block recursive algorithm is proposed to calculate these three motion parameters with compensating the variety of block position to get better stability. To get the simplification requirement for hardware implementation, the representation accuracy of displaced frame difference and gradient that are given is analyzed, From these analysis we propose a quantized block recursive algorithm with quantized grandient to reduce the computational complexity. With this simplification the quantized motion estimation algorithm could get sufficient computational speed to meet the requirement of real time application with the least accuracy loss.
Motion parameter estimation based on the block recursive algorithm with finite word length
(1997-11-01)
Liu, PC
;
Chang, WT
;
Shen, WZ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Three parameter motion model can better describe the motion trajectory of picture element in video sequence. Combining the features of block process and recursive estimation, a block recursive algorithm is proposed to calculate these three motion parameters with compensating the variety of block position to get better stability. To get the simplification requirement for hardware implementation, the representation accuracy of displaced frame difference and gradient that are given is analyzed, From these analysis we propose a quantized block recursive algorithm with quantized grandient to reduce the computational complexity. With this simplification the quantized motion estimation algorithm could get sufficient computational speed to meet the requirement of real time application with the least accuracy loss.
Multigrid computation for curve fitting in the wavelet domain
(1998-03-05)
Ho, WJ
;
Chang, WT
;
電信工程研究所
;
Institute of Communications Engineering
A multi-layer multigrid algorithm for curve fitting in the wavelet domain is presented. This algorithm is achieved by applying a wavelet transform to each grid of the conventional multigrid structure. Using a wavelet transform, the convergent rate in each grid is improved and the total system can converge more quickly.
Petri net-based analysis on object assignment in distributed object-oriented systems
(1998-09-01)
Chang, WT
;
Tseng, CC
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Chou, WK
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資訊工程學系
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Department of Computer Science
Object-oriented programming [9], which treats objects as processes in execution, has shown significant effectiveness in distributed systems. This effectiveness is greatly influenced by how objects are assigned to nodes. In this paper, we present a colored generalized stochastic Petri net (CGSPN) model to analyze the behavior of object invocations when an assignment strategy is applied. The effectiveness of an object assignment is also analyzed by our CGSPN model. Moreover, this analysis provides guidelines to develop an efficient object assignment strategy. [4-8].
Quantization noise reduction for DCT coded images
(2004-08-01)
Kuo, CC
;
Chang, WT
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電信工程研究所
;
Institute of Communications Engineering
By modelling the quantization error as additive white noise in the transform domain, Wiener filter is used to reduce quantization noise for DCT coded images in DCT domain. Instead of deriving the spectrum of the transform coefficient, a DPCM loop is used to whiten the quantized DCT coefficients. The DPCM loop predicts the mean for each coefficient. By subtracting the mean, the quantized DCT coefficient is converted into the sum of prediction error and quantization noise. After the DPCM loop, the prediction error can be assumed uncorrelated to make the design of the subsequent Wiener filter easy. The Wiener filter is applied to remove the quantization noise to restore the prediction error. The original coefficient is reconstructed by adding the DPCM predicted mean with the restored prediction error. To increase the prediction accuracy, the decimated DCT coefficients in each subband are interpolated from the overlapped blocks.
Recursive minimum energy algorithm for image interpolation
(1998-02-01)
Liu, PC
;
Chang, WT
;
Shen, WZ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An interpolation method based on the criterion to maximize the smoothness is proposed. In contrast to the conventional approach, where the interpolated signal is made smooth by low-pass filtering, in the proposed method, the smoothness is obtained by minimizing a global energy function. With the minimum energy formulation for interpolation, a recursive method is used to derive the solution and named as the recursive minimum energy algorithm. Because the smoothness is improved by increasing the calculation iteration but not by increasing the tap length, the controllability of this system is increased. Experiments show that the smoothness and the frequency performance obtained by the proposed algorithm are better than those of the conventional method. Also, the corresponding architecture design for the image interpolation is presented and shown to be suit for VLSI implemented.
Recursive minimum energy algorithm for image interpolation
(1998-02-01)
Liu, PC
;
Chang, WT
;
Shen, WZ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An interpolation method based on the criterion to maximize the smoothness is proposed. In contrast to the conventional approach, where the interpolated signal is made smooth by low-pass filtering, in the proposed method, the smoothness is obtained by minimizing a global energy function. With the minimum energy formulation for interpolation, a recursive method is used to derive the solution and named as the recursive minimum energy algorithm. Because the smoothness is improved by increasing the calculation iteration but not by increasing the tap length, the controllability of this system is increased. Experiments show that the smoothness and the frequency performance obtained by the proposed algorithm are better than those of the conventional method. Also, the corresponding architecture design for the image interpolation is presented and shown to be suit for VLSI implemented.
Recursive wiener filter for motion parameter estimation in three-parameter motion model
(1998-12-01)
Liu, PC
;
Chang, WT
;
資訊工程學系
;
Department of Computer Science
Motion compensation is used to reduce the displaced frame difference (DFD) during the video coding. To increase the accuracy of the point correspondence during the compensation, a three-parameter motion model is considered. The matching error can be significantly reduced as compared with that of the two-parameter block matching. To derive the parameters, a partial full search method is used. The full search is used when the zoom value is set at one. Otherwise, the gradient-based algorithm is used, Since the DFD is a nonlinear function of the image gradients and the motion parameters, a linearized model is considered. To eliminate the linearization error, Wiener filtering is used to smoothen the DFD to improve the convergence condition of the iterative gradient search. To make the gradient-based search more robust to the gradient variation, several gradient estimation methods are also compared.
Recursive wiener filter for motion parameter estimation in three-parameter motion model
(1998-12-01)
Liu, PC
;
Chang, WT
;
資訊工程學系
;
Department of Computer Science
Motion compensation is used to reduce the displaced frame difference (DFD) during the video coding. To increase the accuracy of the point correspondence during the compensation, a three-parameter motion model is considered. The matching error can be significantly reduced as compared with that of the two-parameter block matching. To derive the parameters, a partial full search method is used. The full search is used when the zoom value is set at one. Otherwise, the gradient-based algorithm is used, Since the DFD is a nonlinear function of the image gradients and the motion parameters, a linearized model is considered. To eliminate the linearization error, Wiener filtering is used to smoothen the DFD to improve the convergence condition of the iterative gradient search. To make the gradient-based search more robust to the gradient variation, several gradient estimation methods are also compared.
Switching level optimization for adaptive modulation
(2004)
Lai, L
;
Yeh, C
;
Chang, WT
;
電信工程研究所
;
Institute of Communications Engineering
Two formulations that are commonly used in the determination of the switching levels are the Torrance cost function and the Lagrangian optimization. From the Lagrangian optimization, it can be seen that the switching levels can be each separately related to the target bit error rate with the constraint that the average bit error satisfies the target bit error requirement. This provides a search direction for the optimum solution of the Torrance formulation. Also, it is verified that if the target bit error is neglected, the Torrance formulation can find the optimum solution for the possible lowest bit error rate. In this case, each switching level is only related to two adjacent modulation modes. Based on this relation, we approximate the Torrance formulation with a two-mode one-dimensional search problem. From this decomposition, we further develop a one mode cost function to evaluate the cost of using one specific modulation mode as a function of instantaneous SNR. Switching levels can be determined by simply comparing these one mode cost function.
Wiener filter for zoom parameter estimation in three-parameter motion model
(1997)
Liu, PC
;
Shen, WZ
;
Chang, WT
;
交大名義發表
;
電子工程學系及電子研究所
From the linearized Taylor series expansion, an iterative, gradient-based method is used to estimate the zoom and pan motion parameters. In order to take into account the high order expansion error, the Wiener filtering techniques are investigated. It is shown that the expansion error can be efficiently removed with the Wiener filter. However, the reliability of the estimated parameters is still highly dependent upon the accuracy of the gradient information of the images.