臺灣博碩士論文加值系統

隨著科技的發展，多媒體的需求也與日俱增，很多用戶端的設備都需要多媒體的服務，隨著設備的不同所需的視訊訊號的解析度也會跟著不同，因此一個可以提供快速變換解析度的解碼器便異常重要。現在多數的解決辦法都朝向直接在離散餘弦轉換域上作解析度轉換的工作，但是大多數的論文都只提到如何對2的倍數做快速解調變，在這一篇論文裡，我們將提到如何快速的將視訊或影像訊號在離散餘弦轉換域上做任意倍數的解析度變換。
我們將提出一個方法可以在離散餘弦轉換域上對一數列做內插或壓縮的方法，這一個方法並不會增加原來的運算量，因為這一個方法只是把原來的數列乘上一常數，而這一個步驟可以跟轉碼器裡的量化步驟做在一起，接下來就是利用離散餘弦轉換本身的對稱性質對一個較小的離散餘弦轉換方塊做對應的反離散餘弦轉換然後把這些小塊的方塊組合成一塊大一點的方塊再對他做對應的離散餘弦轉換，由於選擇特殊的大小去做離散餘弦轉換和反離散餘弦轉換，所以相乘的結果可以使得最後的結果有很多零的項，而零的項並不會增加計算量，利用這一個特性可以使得計算量大大的減少，然後把我們的結果跟用雙線性的方法做出來的結果來比較會發現我們的結果的計算量少很多，而且我們方法的PSNR也比較高，因此我們的方法有比較好的結果。

Due to the advances in technology, the demand on transmission of multimedia becomes greater than ever. Many subscriber devices need the service of transmitting multimedia. According to the resolution of each device, the resolution of the video will need to adapt to the specific device. Hence a transcoder which will provide the service of translating resolution efficiently becomes more and more important. Recently, most researches concentrate on translating the resolution in the DCT-Domain. However, most papers just dealt with how to scale the picture by “2”. In this thesis we will propose a fast algorithm on resolution translation in DCT-domain for any scale factors.
We first propose a method to interpolate or decimate the DCT-domain sequence. This method won’t increase the original calculation capability, because the method needs to only multiply the original sequence by a scalar term, and this step can be combined into the quantization step in the transcoder. Then we take advantage of the symmetric property of DCT, preserve fewer low-frequency coefficients, and transform them back to spatial domain using smaller DCT. Then combine a proper number of them into a bigger block and transform them into DCT-domain using the proper DCT. Because we choose the size of block carefully, we will have many zero terms in the resulting matrices. Using this result we can save computation dramatically. Finally we compare our result with the bilinear scheme, and find that our scheme will have higher PSNR values and fewer calculation demand.

Abstract i
Table of Contents ii
List of Figures iv
Chapter 1: Introduction 1
1.1 Overview 1
1.2 Thesis Organization 3
Chapter 2: Overview of DCT-domain Video Transcoder 4
2.1 Structure of Video Transcoder 4
2.2 DCT Motion Compensation 7
2.2.1 DCT Properties 7
2.2.2 MC-DCT 7
2.2.3 MC-DCT using shared information 10
Chapter 3: Resolution Translation 14
3.1 Approach I 14
3.2 Approach II 16
Chapter 4: Decimation and Interpolation in DCT Domain 22
4.1 DTFT and DFT interpolation 22
4.2 DTFT and DFT decimation 25
4.3 Decimation and interpolation in DCT-domain 27
Chapter 5: DCT-Domain Image Size Change 35
5.1 Te Basic Idea 35
5.2 Down Sampling 42
5.2.1 Procedure 42
5.2.2 Mathematical Representation 45
5.3 Up Sampling 47
5.3.1 Procedure 47
5.3.2 Mathematical Representation 50
5.4 Complexity 52
Chapter 6: Simulation Result 54
Chapter 7: Conclusions and future works 65
References 67

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