Browsing by Author "Ho, WJ"

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Adaptive interpolator with context modeling in lifting scheme for lossless coding
(2000)
Chang, WT
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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).
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.