Wavelet-Based Image Compression with Modified Search Order Coding and Crossband Vector Quantization
| Autor: | Jung-Chung Hsu, 許榮忠 |
|---|---|
| Rok vydání: | 2000 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 88 The discrete wavelet transform (DWT) is a powerful technique for image compression because of its flexibility in representing image and its ability is adapting to the human visual system characteristics. This thesis presents a new compression technique for the wavelet transformed coefficients, which mainly contains a modified search order coding (SOC) for lowest band and crossband vector quantization (VQ) for higher bands. Search-order coding (SOC) is an efficient technique originally designed for the compression of VQ indexes. This thesis modifies the SOC for efficiently coding the lowest band of the wavelet coefficients. For an input coefficient, a searching scheme is employed to find out the matched coefficient from the previous coefficient and then the corresponding search order of the matched coefficient is sent to the decoder. The search order is encoded with a simple and efficient variable-length code. In wavelet domain, there exists correlation among the coefficients of different resolution levels (or scales). This thesis employs a crossband vector quantization technique to exploit the correlation efficiently. It defines three independent 21-dimensional VQs to encode nine higher resolution bands. The output symbols of the SOC and crossband VQ are further encoded with several specially designed arithmetic coders, which improve the compression efficiency significantly. The simulation results indicate that the new wavelet-based technique achieves good picture quality at very low bit rate. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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