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標題: 嵌入式傳真伺服器設計與小波壓縮於此系統中的應用
The Design of Embedded Fax Server and The Application of Wavelet in the System
作者: 林志鴻
Lin, Jyh-Horng
關鍵字: G3;G3;G4;MH;MR;MMR;fax;wavelet transform;context modeling;arithmetic coding;G4;MH;MR;MMR;傳真;小波轉換;上下文模型;算術編碼
出版社: 電機工程學系
影像壓縮為傳真機高速傳送時不可或缺的技術,CCITT所公布之G3、G4傳真機的編碼方式MH(Modified Huffman)、MR(Modified Read)、MMR(Modified MR)是在空間領域上作壓縮,是根據統計結果設計出的編碼表作編碼來達到壓縮目的,故其壓縮效果對於一般的文件可以說相當的良好,但是對於圖形的文件就不是很理想,因此將針對這方面來加以改善。

A fax server integrates the functionality of a fax machine into network. It can receive fax, then e-mail the received documents to administrator's mail box by attaching the files into the mail. Users can preview the documents, then decide whether to print it or not. It is both environment friendly and economical. It can be used in families, schools and companies, and make fax more popular.
Image compression is a crucial part of the fax process. The coding modes published by CCITT was G3 and G4. They used MH(Modified Huffman), MR(Modified Read) and MMR(Modified MR). All of them compress in spatial domain. The compression is achieved by encoding the scanned documents using predefined table determined by statistics in text documents. The compression ratio is generally good for text documents but it is not suitable for graphics and images. Therefore, we will improve it in the thesis.
The thesis uses wavelet transform to compress the fax documents. First, we use wavelet to transform the images. Then, we use context modeling to classify the transformed images. The goal of the classification is to make the probability in each class biases to a certain range. Finally, we use arithmetic coding to encode the images. We expect that it can achieve better compression ratio than the fax standard.
In the experiments, when we process general text documents, the compression ratio of wavelet is close to G3 encoding. When we process tables, the compression ratio of wavelet is better than G3 encoding. Although it's not better than G4 encoding in texts or tables, it's better than G3 and G4 encoding in graphics and images. We believe that using wavelet in fax compression is a good choice because it achieves a good balance between texts and images.
Appears in Collections:電機工程學系所

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